LM2742MTC/NOPB - NATIONAL SEMICONDUCTOR

LM2742

LM2742 N-Channel FET Synchronous Buck Regulator Controller for Low Output

Voltages

Literature Number: SNVS266B

October 31, 2007

LM2742

N-Channel FET Synchronous Buck Regulator Controller

for Low Output Voltages

General Description

The LM2742 is a high-speed, synchronous, switching regu-

lator controller. It is intended to control currents of 0.7A to 20A

with up to 95% conversion efficiencies. Power up and down

sequencing is achieved with the power-good flag, adjustable

soft-start and output enable features. The LM2742 operates

from a low-current 5V bias and can convert from a 1V to 16V

power rail. The part utilizes a fixed-frequency, voltage-mode,

PWM control architecture and the switching frequency is ad-

justable from 50kHz to 2MHz by setting the value of an

external resistor. Current limit is achieved by monitoring the

voltage drop across the on-resistance of the low-side MOS-

FET, which enables on-times on the order of 40ns, one of the

best in the industry. The wide range of operating frequencies

gives the power supply designer the flexibility to fine-tune

component size, cost, noise and efficiency. The adaptive,

non-overlapping MOSFET gate-drivers and high-side boot-

strap structure helps to further maximize efficiency. The high-

side power FET drain voltage can be from 1V to 16V and the

output voltage is adjustable down to 0.6V.

Features

■Input power from 1V to 16V

■Output voltage adjustable down to 0.6V

■Power Good flag, adjustable soft-start and output enable

for easy power sequencing

■Reference Accuracy: 1.5% (0°C - 125°C)

■Current limit without sense resistor

■Soft start

■Switching frequency from 50 kHz to 2 MHz

■40ns typical minimum on-time

■TSSOP-14 package

Applications

■POL power supply modules

■Cable Modems

■Set-Top Boxes/ Home Gateways

■DDR Core Power

■High-Efficiency Distributed Power

■Local Regulation of Core Power

Typical Application

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LM2742 N-Channel FET Synchronous Buck Regulator Controller for Low Output Voltages

Connection Diagram

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14-Lead Plastic TSSOP

θJA = 155°C/W

Ordering Information

Order Number Package Type NSC Package Drawing Supplied As

LM2742MTC TSSOP-14 MTC14 94 Units, Raill

LM2742MTCX TSSOP-14 MTC14 2500 Units on Tape and Reel

Pin Descriptions

BOOT (Pin 1) - Supply rail for the N-channel MOSFET gate

drive. The voltage should be at least one gate threshold above

the regulator input voltage to properly turn on the high-side N-

FET.

LG (Pin 2) - Gate drive for the low-side N-channel MOSFET.

This signal is interlocked with HG to avoid shoot-through

problems.

PGND (Pins 3, 13) - Ground for FET drive circuitry. It should

be connected to system ground.

SGND (Pin 4) - Ground for signal level circuitry. It should be

connected to system ground.

VCC (Pin 5) - Supply rail for the controller.

PWGD (Pin 6) - Power Good. This is an open drain output.

The pin is pulled low when the chip is in UVP, OVP, or UVLO

mode. During normal operation, this pin is connected to VCC

or other voltage source through a pull-up resistor.

ISEN (Pin 7) - Current limit threshold setting. This sources a

fixed 50µA current. A resistor of appropriate value should be

connected between this pin and the drain of the low-side FET.

EAO (Pin 8) - Output of the error amplifier. The voltage level

on this pin is compared with an internally generated ramp

signal to determine the duty cycle. This pin is necessary for

compensating the control loop.

SS (Pin 9) - Soft start pin. A capacitor connected between this

pin and ground sets the speed at which the output voltage

ramps up. Larger capacitor value results in slower output volt-

age ramp but also lower inrush current.

FB (Pin 10) - This is the inverting input of the error amplifier,

which is used for sensing the output voltage and compensat-

ing the control loop.

FREQ (Pin 11) - The switching frequency is set by connecting

a resistor between this pin and ground.

SD (Pin 12) - IC Logic Shutdown. When this pin is pulled low

the chip turns off both the high side and low side switches.

While this pin is low, the IC will not start up. An internal 20µA

pull-up connects this pin to VCC. For a device which turns on

the low side switch during shutdown, see the pin compatible

LM2737.

HG (Pin 14) - Gate drive for the high-side N-channel MOS-

FET. This signal is interlocked with LG to avoid shoot-through

problems.

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LM2742

Absolute Maximum Ratings (Note 1)

If Military/Aerospace specified devices are required,

please contact the National Semiconductor Sales Office/

Distributors for availability and specifications.

VCC 7V

BOOTV 21V

LG and HG to GND (Note 3) -2V to 21V

Junction Temperature 150°C

Storage Temperature −65°C to 150°C

Soldering Information

Lead Temperature

(soldering, 10sec) 260°C

Infrared or Convection (20sec) 235°C

ESD Rating 2 kV

Operating Ratings

Supply Voltage (VCC)4.5V to 5.5V

Junction Temperature Range −40°C to +125°C

Thermal Resistance (θJA)155°C/W

Electrical Characteristics

VCC = 5V unless otherwise indicated. Typicals and limits appearing in plain type apply for TA=TJ=+25°C. Limits appearing in boldface

type apply over full Operating Temperature Range. Datasheet min/max specification limits are guaranteed by design, test, or

statistical analysis.

Symbol Parameter Conditions Min Typ Max Units

VFB_ADJ FB Pin Voltage

VCC = 4.5V, 0°C to +125°C 0.591 0.6 0.609

VCC = 5V, 0°C to +125°C 0.591 0.6 0.609

VCC = 5.5V, 0°C to +125°C 0.591 0.6 0.609

VCC = 4.5V, −40°C to +125°C 0.589 0.6 0.609

VCC = 5V, −40°C to +125°C 0.589 0.6 0.609

VCC = 5.5V, −40°C to +125°C 0.589 0.6 0.609

VON UVLO Thresholds Rising

Falling

4.2

3.6

IQ-V5

Operating VCC Current

SD = 5V, FB = 0.55V

Fsw = 600kHz 11.5 2

SD = 5V, FB = 0.65V

Fsw = 600kHz 0.8 1.7

2.2

Shutdown VCC Current SD = 0V 0.15 0.4 0.7 mA

tPWGD1 PWGD Pin Response Time FB Voltage Going Up 6 µs

tPWGD2 PWGD Pin Response Time FB Voltage Going Down 6 µs

ISD SD Pin Internal Pull-up Current 20 µA

ISS-ON SS Pin Source Current SS Voltage = 2.5V

0°C to +125°C

-40°C to +125°C

µA

ISS-OC SS Pin Sink Current During Over

Current

SS Voltage = 2.5V 95 µA

ISEN-TH

ISEN Pin Source Current Trip Point 0°C to +125°C

-40°C to +125°C

65 µA

ERROR AMPLIFIER

GBW Error Amplifier Unity Gain

Bandwidth

5 MHz

G Error Amplifier DC Gain 60 dB

SR Error Amplifier Slew Rate 6 V/µA

IFB FB Pin Bias Current FB = 0.55V

FB = 0.65V

100

155 nA

IEAO EAO Pin Current Sourcing and

Sinking

VEAO = 2.5, FB = 0.55V

VEAO = 2.5, FB = 0.65V

2.8

0.8

VEA Error Amplifier Maximum Swing Minimum

Maximum

1.2

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LM2742

Symbol Parameter Conditions Min Typ Max Units

GATE DRIVE

IQ-BOOT BOOT Pin Quiescent Current BOOT = 12V, EN = 0

0°C to +125°C

-40°C to +125°C

160

215

µA

RDS1 Top FET Driver Pull-Up ON

resistance BOOT-SW = 5V@350mA 3 Ω

RDS2 Top FET Driver Pull-Down ON

resistance BOOT-SW = 5V@350mA 2 Ω

RDS3 Bottom FET Driver Pull-Up ON

resistance BOOT-SW = 5V@350mA 3 Ω

RDS4 Bottom FET Driver Pull-Down ON

resistance BOOT-SW = 5V@350mA 2 Ω

OSCILLATOR

fOSC PWM Frequency

RFADJ = 590kΩ 50

kHz

RFADJ = 88.7kΩ 300

RFADJ = 42.2kΩ, 0°C to +125°C 500 600 700

RFADJ = 42.2kΩ, -40°C to +125°C 490 600 700

RFADJ = 17.4kΩ 1400

RFADJ = 11.3kΩ 2000

D Max Duty Cycle fPWM = 300kHz

fPWM = 600kHz

ton-min Minimum on-time 40 ns

LOGIC INPUTS AND OUTPUTS

VSD-IH SD Pin Logic High Trip Point 2.6 3.5 V

VSD-IL SD Pin Logic Low Trip Point 0°C to +125°C

-40°C to +125°C

1.3

1.25

1.6

VPWGD-TH-LO PWGD Pin Trip Points FB Voltage Going Down

0°C to +125°C

-40°C to +125°C

0.413

0.410

0.430

0.446

VPWGD-TH-HI PWGD Pin Trip Points FB Voltage Going Up

0°C to +125°C

-40°C to +125°C

0.691

0.688

0.710

0.734

VPWGD-HYS PWGD Hysteresis FB Voltage Going Down FB Voltage

Going Up

110

Note 1: Absolute maximum ratings indicate limits beyond which damage to the device may occur. Operating ratings indicate conditions for which the device

operates correctly. Operating Ratings do not imply guaranteed performance limits.

Note 2: The human body model is a 100pF capacitor discharged through a 1.5k resistor into each pin.

Note 3: The LG and HG pin can have -2V to -0.5V applied for a maximum duty cycle of 10% with a maximum period of 1 second. There is no duty cycle or

maximum period limitation for a LG and HG pin voltage range of -0.5V to 21V.

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LM2742

Typical Performance Characteristics

Efficiency (VO = 1.5V)

FSW = 300kHz, TA = 25°C

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Efficiency (VO = 3.3V)

FSW = 300kHz, TA = 25°C

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VCC Operating Current vs Temperature

FSW = 600kHz, No-Load

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Bootpin Current vs Temperature for BOOTV = 12V

FSW = 600kHz, Si4826DY FET, No-Load

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Bootpin Current vs Temperature with 5V Bootstrap

FSW = 600kHz, Si4826DY FET, No-Load

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PWM Frequency vs Temperature

for RFADJ = 43.2kΩ

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LM2742

RFADJ vs PWM Frequency

(in 100 to 800kHz range), TA = 25°C

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RFADJ vs PWM Frequency

(in 900 to 2000kHz range), TA = 25°C

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VCC Operating Current Plus Boot Current vs

PWM Frequency (Si4826DY FET, TA = 25°C)

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Switch Waveforms (HG Falling)

VIN = 5V, VO = 1.8V

IO = 3A, CSS = 10nF

FSW = 600kHz

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Switch Waveforms (HG Rising)

VIN = 5V, VO = 1.8V

IO = 3A, FSW = 600kHz

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Start-Up (No-Load)

VIN = 10V, VO = 1.2V

CSS = 10nF, FSW = 300kHz

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LM2742

Start-Up (Full-Load)

VIN = 10V, VO = 1.2V

IO = 10A, CSS = 10nF

FSW = 300kHz

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Start Up (No-Load, 10x CSS)

VIN = 10V, VO = 1.2V

CSS = 100nF, FSW = 300kHz

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Start Up (Full Load, 10x CSS)

VIN = 10V, VO = 1.2V

IO = 10A, CSS = 100nF

FSW = 300kHz

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Start Up (Into 1.2V Pre-Bias)

VIN = 12V, VO = 2.5V

No Load, No Soft Start Capacitor

FSW = 300kHz

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Start Up (Into 1.2V Pre-Bias)

VIN = 12V, VO = 2.5V

No Load, CSS = 10nF

FSW = 300kHz

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Shutdown

VIN = 12V, VO = 1.2V

IO = 10A, CSS = 10nF

FSW = 300kHz

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LM2742

Shutdown (No Load)

VIN = 12V, VO = 1.2V

IO = 10A, CSS = 10nF

FSW = 300kHz

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Load Transient Response (IO = 0 to 4A)

VIN = 12V, VO = 1.2V

FSW = 300kHz

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Load Transient Response (IO = 4 to 0A)

VIN = 12V, VO = 1.2V

FSW = 300kHz

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Line Transient Response (VIN =5V to 12V)

VO = 1.2V, IO = 5A

FSW = 300kHz

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Line Transient Response (VIN =12V to 5V)

VO = 1.2V, IO = 5A

FSW = 300kHz

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Line Transient Response

VO = 1.2V, IO = 5A

FSW = 300kHz

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LM2742

Peak Current During Current Limit

VIN = 12V, VO = 3.3V, ILIM = 4A, FSW = 300kHz, L = 15 µH

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Peak Current During Current Limit

VIN = 12V, VO = 3.3V, ILIM = 4A, FSW = 300kHz, L = 15 µH

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Block Diagram

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LM2742

Application Information

THEORY OF OPERATION

The LM2742 is a voltage-mode, high-speed synchronous

buck regulator with a PWM control scheme. It is designed for

use in set-top boxes, thin clients, DSL/Cable modems, and

other applications that require high efficiency buck convert-

ers. It has power good (PWRGD), and output shutdown

(SD). Current limit is achieved by sensing the voltage VDS

across the low side FET. During current limit the high side

gate is turned off and the low side gate turned on. The soft

start capacitor is discharged by a 95µA source (reducing the

maximum duty cycle) until the current is under control.

START UP

When VCC exceeds 4.2V and the shutdown pin SD sees a

logic high the soft start capacitor begins charging through an

internal fixed 10µA source. During this time the output of the

error amplifier is allowed to rise with the voltage of the soft

start capacitor. This capacitor, CSS, determines soft start time,

and can be determined approximately by:

An application for a microprocessor might need a delay of

3ms, in which case CSS would be 12nF. For a different device,

a 100ms delay might be more appropriate, in which case

CSS would be 400nF. (390 10%) During soft start the PWRGD

flag is forced low and is released when the voltage reaches a

set value. At this point this chip enters normal operation mode

and the Power Good flag is released.

Since the output is floating when the LM2742 is turned off, it

is possible that the output capacitor may be precharged to

some positive value. During start-up, the LM2742 operates

fully synchronous and will discharge the output capacitor to

some extent depending on the output voltage, soft start ca-

pacitance, and the size of the output capacitor.

NORMAL OPERATION

While in normal operation mode, the LM2742 regulates the

output voltage by controlling the duty cycle of the high side

and low side FETs. The equation governing output voltage is:

VO = 0.6 x (RFB1 + RFB2) / RFB1

The PWM frequency is adjustable between 50kHz and 2MHz

and is set by an external resistor, RFADJ, between the FREQ

pin and ground. The resistance needed for a desired frequen-

cy is approximately:

MOSFET GATE DRIVERS

The LM2742 has two gate drivers designed for driving N-

channel MOSFETs in a synchronous mode. Power for the

drivers is supplied through the BOOT pin. For the high side

gate (HG) to fully turn on the top FET, the BOOT voltage must

be at least one VGS(th) greater than Vin. (BOOT ≥ 2*Vin) This

voltage can be supplied by a separate, higher voltage source,

or supplied from a local charge pump structure. In a system

such as a desktop computer, both 5V and 12V are usually

available. Hence if Vin was 5V, the 12V supply could be used

for BOOT. 12V is more than 2*Vin, so the HG would operate

correctly. For a BOOT of 12V, the initial gate charging current

is 2A, and the initial gate discharging current is typically 6A.

20087502

FIGURE 1. BOOT Supplied by Charge Pump

In a system without a separate, higher voltage, a charge pump

(bootstrap) can be built using a diode and small capacitor,

Figure 1. The capacitor serves to maintain enough voltage

between the top FET gate and source to control the device

even when the top FET is on and its source has risen up to

the input voltage level.

The LM2742 gate drives use a BiCMOS design. Unlike some

other bipolar control ICs, the gate drivers have rail-to-rail

swing, ensuring no spurious turn-on due to capacitive cou-

pling.

POWER GOOD SIGNAL

The power good signal is the or-gated flag representing over-

voltage and under-voltage protection. If the output voltage is

18% over it's nominal value, VFB = 0.7V, or falls 30% below

that value, VFB = 0.41V, the power good flag goes low. It will

return to a logic high whenever the feedback pin voltage is

between 70% and 118% of 0.6V. The power good pin is an

open drain output that can be pulled up to logic voltages of

5V or less with a 10kΩ resistor.

UVLO

The 4.2V turn-on threshold on VCC has a built in hysteresis of

0.6V. Therefore, if VCC drops below 3.6V, the chip enters UV-

LO mode. UVLO consists of turning off the top FET, turning

off the bottom FET, and remaining in that condition until VCC

rises above 4.2V. As with shutdown, the soft start capacitor

is discharged through a FET, ensuring that the next start-up

will be smooth.

CURRENT LIMIT

Current limit is realized by sensing the voltage across the low

side FET while it is on. The RDSON of the FET is a known value,

hence the current through the FET can be determined as:

VDS = I * RDSON

The current through the low side FET while it is on is also the

falling portion of the triangle wave inductor current. The cur-

rent limit threshold is determined by an external resistor,

RCS, connected between the switch node and the ISEN pin. A

constant current of 50 µA is forced through RCS, causing a

fixed voltage drop. This fixed voltage is compared against

VDS and if the latter is higher, the current limit of the chip has

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LM2742

been reached. RCS can be found by using the following equa-

tion:

RCS = RDSON(LOW) * ILIM/50µA

For example, a conservative 15A current limit in a 10A design

with a minimum RDSON of 10mΩ would require a 3.3kΩ resis-

tor. Because current sensing is done across the low side FET,

no minimum high side on-time is necessary. In the current

limit mode the LM2727/37 will turn the high side off and the

keep low side on for as long as necessary. The LM2727/37

enters current limit mode if the inductor current exceeds the

current limit threshold at the point where the high side FET

turns off and the low side FET turns on. (The point of peak

inductor current. See .) Note that in normal operation mode

the high side FET always turns on at the beginning of a clock

cycle. In current limit mode, by contrast, the high side FET on

pulse is skipped. This causes inductor current to fall. Unlike

a normal operation switching cycle, however, in a current limit

mode switching cycle the high side FET will turn on as soon

as inductor current has fallen to the current limit threshold.

The LM2727/37 will continue to skip high side FET pulses until

the inductor current peak is below the current limit threshold,

at which point the system resumes normal operation.

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FIGURE 2. Current Limit Threshold

Unlike a high side FET current sensing scheme, which limits

the peaks of inductor current, low side current sensing is only

allowed to limit the current during the converter off-time, when

inductor current is falling. Therefore in a typical current limit

plot the valleys are normally well defined, but the peaks are

variable, according to the duty cycle. The PWM error amplifier

and comparator control the off pulse of the high side FET,

even during current limit mode, meaning that peak inductor

current can exceed the current limit threshold. Assuming that

the output inductor does not saturate, the maximum peak in-

ductor current during current limit mode can be calculated

with the following equation:

Where TOSC is the inverse of switching frequency fOSC. The

200ns term represents the minimum off-time of the duty cycle,

which ensures enough time for correct operation of the cur-

rent sensing circuitry. See the plots entitled Peak Current

During Current Limit in the Typical Performance Characteris-

tics section.

In order to minimize the time period in which peak inductor

current exceeds the current limit threshold, the IC also dis-

charges the soft start capacitor through a fixed 95 µA source.

The output of the LM2727/37 internal error amplifier is limited

by the voltage on the soft start capacitor. Hence, discharging

the soft start capacitor reduces the maximum duty cycle D of

the controller. During severe current limit this reduction in duty

cycle will reduce the output voltage if the current limit condi-

tions last for an extended time. Output inductor current will be

reduced in turn to a flat level equal to the current limit thresh-

old. The third benefit of the soft start capacitor discharge is a

smooth, controlled ramp of output voltage when the current

limit condition is cleared. During the first few nanoseconds

after the low side gate turns on, the low side FET body diode

conducts. This causes an additional 0.7V drop in VDS. The

range of VDS is normally much lower. For example, if RDSON

were 10mΩ and the current through the FET was 10A, VDS

would be 0.1V. The current limit would see 0.7V as a 70A

current and enter current limit immediately. Hence current

limit is masked during the time it takes for the high side switch

to turn off and the low side switch to turn on.

SHUT DOWN

If the shutdown pin SD is pulled low, the LM2742 discharges

the soft start capacitor through a MOSFET switch. The high

side and low side switches are turned off. The LM2742 re-

mains in this state until SD is released.

DESIGN CONSIDERATIONS

The following is a design procedure for all the components

needed to create the circuit shown in Figure 4 in the Example

Circuits section, a 5V in to 1.2V out converter, capable of de-

livering 10A with an efficiency of 85%. The switching frequen-

cy is 300kHz. The same procedures can be followed to create

many other designs with varying input voltages, output volt-

ages, and output currents.

Input Capacitor

The input capacitors in a Buck switching converter are sub-

jected to high stress due to the input current waveform, which

is a square wave. Hence input caps are selected for their rip-

ple current capability and their ability to withstand the heat

generated as that ripple current runs through their ESR. Input

rms ripple current is approximately:

The power dissipated by each input capacitor is:

Here, n is the number of capacitors, and indicates that power

loss in each cap decreases rapidly as the number of input

caps increase. The worst-case ripple for a Buck converter

occurs during full load, when the duty cycle D = 50%.

In the 5V to 1.2V case, D = 1.2/5 = 0.24. With a 10A maximum

load the ripple current is 4.3A. The Sanyo 10MV5600AX alu-

minum electrolytic capacitor has a ripple current rating of

2.35A, up to 105°C. Two such capacitors make a conserva-

tive design that allows for unequal current sharing between

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LM2742

individual caps. Each capacitor has a maximum ESR of

18mΩ at 100 kHz. Power loss in each device is then 0.05W,

and total loss is 0.1W. Other possibilities for input and output

capacitors include MLCC, tantalum, OSCON, SP, and

POSCAPS.

Input Inductor

The input inductor serves two basic purposes. First, in high

power applications, the input inductor helps insulate the input

power supply from switching noise. This is especially impor-

tant if other switching converters draw current from the same

supply. Noise at high frequency, such as that developed by

the LM2742 at 1MHz operation, could pass through the input

stage of a slower converter, contaminating and possibly in-

terfering with its operation.

An input inductor also helps shield the LM2742 from high fre-

quency noise generated by other switching converters. The

second purpose of the input inductor is to limit the input cur-

rent slew rate. During a change from no-load to full-load, the

input inductor sees the highest voltage change across it,

equal to the full load current times the input capacitor ESR.

This value divided by the maximum allowable input current

slew rate gives the minimum input inductance:

In the case of a desktop computer system, the input current

slew rate is the system power supply or "silver box" output

current slew rate, which is typically about 0.1A/µs. Total input

capacitor ESR is 9mΩ, hence ΔV is 10*0.009 = 90 mV, and

the minimum inductance required is 0.9µH. The input inductor

should be rated to handle the DC input current, which is ap-

proximated by:

In this case IIN-DC is about 2.8A. One possible choice is the

TDK SLF12575T-1R2N8R2, a 1.2µH device that can handle

8.2Arms, and has a DCR of 7mΩ.

Output Inductor

The output inductor forms the first half of the power stage in

a Buck converter. It is responsible for smoothing the square

wave created by the switching action and for controlling the

output current ripple. (ΔIo) The inductance is chosen by se-

lecting between tradeoffs in output ripple, efficiency, and

response time. The smaller the output inductor, the more

quickly the converter can respond to transients in the load

current. If the inductor value is increased, the ripple through

the output capacitor is reduced and thus the output ripple is

reduced. As shown in the efficiency calculations, a smaller

inductor requires a higher switching frequency to maintain the

same level of output current ripple. An increase in frequency

can mean increasing loss in the FETs due to the charging and

discharging of the gates. Generally the switching frequency

is chosen so that conduction loss outweighs switching loss.

The equation for output inductor selection is:

A good range for ΔIo is 25 to 50% of the output current. In the

past, 30% was considered a maximum value for output cur-

rents higher than about 2Amps, but as output capacitor tech-

nology improves the ripple current can be allowed to increase.

Plugging in the values for output current ripple, input voltage,

output voltage, switching frequency, and assuming a 40%

peak-to-peak output current ripple yields an inductance of

1.5µH. The output inductor must be rated to handle the peak

current (also equal to the peak switch current), which is (Io +

0.5*ΔIo). This is 12A for a 10A design. The Coilcraft

D05022-152HC is 1.5µH, is rated to 15Arms, and has a DCR

of 4mΩ.

Output Capacitor

The output capacitor forms the second half of the power stage

of a Buck switching converter. It is used to control the output

voltage ripple (ΔVo) and to supply load current during fast load

transients.

In this example the output current is 10A and the expected

type of capacitor is an aluminum electrolytic, as with the input

capacitors. (Other possibilities include ceramic, tantalum, and

solid electrolyte capacitors, however the ceramic type often

do not have the large capacitance needed to supply current

for load transients, and tantalums tend to be more expensive

than aluminum electrolytic.) Aluminum capacitors tend to

have very high capacitance and fairly low ESR, meaning that

the ESR zero, which affects system stability, will be much

lower than the switching frequency. The large capacitance

means that at switching frequency, the ESR is dominant,

hence the type and number of output capacitors is selected

on the basis of ESR. One simple formula to find the maximum

ESR based on the desired output voltage ripple, ΔVo and the

designed output current ripple, ΔIo, is:

In this example, in order to maintain a 2% peak-to-peak output

voltage ripple and a 40% peak-to-peak inductor current ripple,

the required maximum ESR is 6mΩ. Three Sanyo

10MV5600AX capacitors in parallel will give an equivalent

ESR of 6mΩ. The total bulk capacitance of 16.8mF is enough

to supply even severe load transients. Using the same ca-

pacitors for both input and output also keeps the bill of mate-

rials simple.

Mosfets

MOSFETS are a critical part of any switching controller and

have a direct impact on the system efficiency. In this case the

target efficiency is 85% and this is the variable that will de-

termine which devices are acceptable. Loss from the capac-

itors, inductors, and the LM2742 itself are detailed in the

Efficiency section, and come to about 0.54W. To meet the

target efficiency, this leaves 1.45W for the FET conduction

loss, gate charging loss, and switching loss. Switching loss is

particularly difficult to estimate because it depends on many

factors. When the load current is more than about 1 or 2 amps,

conduction losses outweigh the switching and gate charging

losses. This allows FET selection based on the RDSON of the

FET. Adding the FET switching and gate-charging losses to

the equation leaves 1.2W for conduction losses. The equation

for conduction loss is:

PCnd = D(I2o * RDSON *k) + (1-D)(I2o * RDSON *k)

The factor k is a constant which is added to account for the

increasing RDSON of a FET due to heating. Here, k = 1.3. The

Si4442DY has a typical RDSON of 4.1mΩ. When plugged into

www.national.com 12

LM2742

the equation for PCND the result is a loss of 0.533W. If this

design were for a 5V to 2.5V circuit, an equal number of FETs

on the high and low sides would be the best solution. With the

duty cycle D = 0.24, it becomes apparent that the low side

FET carries the load current 76% of the time. Adding a second

FET in parallel to the bottom FET could improve the efficiency

by lowering the effective RDSON. The lower the duty cycle, the

more effective a second or even third FET can be. For a min-

imal increase in gate charging loss (0.054W) the decrease in

conduction loss is 0.15W. What was an 85% design improves

to 86% for the added cost of one SO-8 MOSFET.

Control Loop Components

The circuit is this design example and the others shown in the

Example Circuits section have been compensated to improve

their DC gain and bandwidth. The result of this compensation

is better line and load transient responses. For the LM2742,

the top feedback divider resistor, Rfb2, is also a part of the

compensation. For the 10A, 5V to 1.2V design, the values are:

Cc1 = 4.7pF 10%, Cc2 = 1nF 10%, Rc = 229kΩ 1%. These

values give a phase margin of 63° and a bandwidth of

29.3kHz.

Support Capacitors and Resistors

The Cinx capacitors are high frequency bypass devices, de-

signed to filter harmonics of the switching frequency and input

noise. Two 1µF ceramic capacitors with a sufficient voltage

rating (10V for the Circuit of Figure 4) will work well in almost

any case.

RIN and CIN are standard filter components designed to en-

sure smooth DC voltage for the chip supply. Depending on

noise, RIN should be 10 to 100Ω, and CIN should be between

0.1 and 2.2 µF. CBOOT is the bootstrap capacitor, and should

be 0.1µF. (In the case of a separate, higher supply to the

BOOT pin, this 0.1µF cap can be used to bypass the supply.)

Using a Schottky device for the bootstrap diode allows the

minimum drop for both high and low side drivers. The On

Semiconductor BAT54 or MBR0520 work well.

Rp is a standard pull-up resistor for the open-drain power

good signal, and should be 10kΩ. If this feature is not neces-

sary, it can be omitted.

RCS is the resistor used to set the current limit. Since the de-

sign calls for a peak current magnitude (Io + 0.5 * ΔIo) of 12A,

a safe setting would be 15A. (This is well below the saturation

current of the output inductor, which is 25A.) Following the

equation from the Current Limit section, use a 3.3kΩ resistor.

RFADJ is used to set the switching frequency of the chip. Fol-

lowing the equation in the Theory of Operation section, the

closest 1% tolerance resistor to obtain fSW = 300kHz is

88.7kΩ.

CSS depends on the users requirements. Based on the equa-

tion for CSS in the Theory of Operation section, for a 3ms

delay, a 12nF capacitor will suffice.

EFFICIENCY CALCULATIONS

A reasonable estimation of the efficiency of a switching con-

troller can be obtained by adding together the loss is each

current carrying element and using the equation:

The following shows an efficiency calculation to complement

the Circuit of Figure 4. Output power for this circuit is 1.2V x

10A = 12W.

Chip Operating Loss

PIQ = IQ-VCC *VCC

2mA x 5V = 0.01W

FET Gate Charging Loss

PGC = n * VCC * QGS * fOSC

The value n is the total number of FETs used. The Si4442DY

has a typical total gate charge, QGS, of 36nC and an rds-on of

4.1mΩ. For a single FET on top and bottom:

2*5*36E-9*300,000 = 0.108W

FET Switching Loss

PSW = 0.5 * Vin * IO * (tr + tf)* fOSC

The Si4442DY has a typical rise time tr and fall time tf of 11

and 47ns, respectively. 0.5*5*10*58E-9*300,000 = 0.435W

FET Conduction Loss

PCn = 0.533W

Input Capacitor Loss

4.282*0.018/2 = 0.164W

Input Inductor Loss

PLin = I2in * DCRinput-L

2.822*0.007 = 0.055W

Output Inductor Loss

PLout = I2o * DCRoutput-L

102*0.004 = 0.4W

System Efficiency

13 www.national.com

LM2742

Example Circuits

20087503

FIGURE 3. 5V-16V to 3.3V, 10A, 300kHz

This circuit and the one featured on the front page have been

designed to deliver high current and high efficiency in a small

package, both in area and in height The tallest component in

this circuit is the inductor L1, which is 6mm tall. The compen-

sation has been designed to tolerate input voltages from 5 to

16V.

20087504

FIGURE 4. 5V to 1.2V, 10A, 300kHz

This circuit design, detailed in the Design Considerations sec-

tion, uses inexpensive aluminum capacitors and off-the-shelf

inductors. It can deliver 10A at better than 85% efficiency.

Large bulk capacitance on input and output ensure stable op-

eration.

www.national.com 14

LM2742

20087505

FIGURE 5. 5V to 1.8V, 3A, 600kHz

The example circuit of Figure 5 has been designed for mini-

mum component count and overall solution size. A switching

frequency of 600kHz allows the use of small input/output ca-

pacitors and a small inductor. The availability of separate 5V

and 12V supplies (such as those available from desk-top

computer supplies) and the low current further reduce com-

ponent count. Using the 12V supply to power the MOSFET

drivers eliminates the bootstrap diode, D1. At low currents,

smaller FETs or dual FETs are often the most efficient solu-

tions. Here, the Si4826DY, an asymmetric dual FET in an

SO-8 package, yields 92% efficiency at a load of 2A.

20087506

FIGURE 6. 3.3V to 0.8V, 5A, 500kHz

The circuit of Figure 6 demonstrates the LM2742 delivering a

low output voltage at high efficiency (87%). A separate 5V

supply is required to run the chip, however the input voltage

can be as low as 2.2

15 www.national.com

LM2742

20087507

FIGURE 7. 1.8V and 3.3V, 1A, 1.4MHz, Simultaneous

The circuits in Figure 7 are intended for ADSL applications,

where the high switching frequency keeps noise out of the

data transmission range. In this design, the 1.8 and 3.3V out-

puts come up simultaneously by using the same softstart

capacitor. Because two current sources now charge the same

capacitor, the capacitance must be doubled to achieve the

same softstart time. (Here, 40nF is used to achieve a 5ms

softstart time.) A common softstart capacitor means that,

should one circuit enter current limit, the other circuit will also

enter current limit. The additional compensation components

Rc2 and Cc3 are needed for the low ESR, all ceramic output

capacitors, and the wide (3x) range of Vin.

www.national.com 16

LM2742

20087508

FIGURE 8. 12V Unregulated to 3.3V, 3A, 750kHz

This circuit shows the LM2742 paired with a cost effective

solution to provide the 5V chip power supply, using no extra

components other than the LM78L05 regulator itself. The in-

put voltage comes from a 'brick' power supply which does not

regulate the 12V line tightly. Additional, inexpensive 10uF ce-

ramic capacitors (Cinx and Cox) help isolate devices with

sensitive databands, such as DSL and cable modems, from

switching noise and harmonics.

20087509

FIGURE 9. 12V to 5V, 1.8A, 100kHz

In situations where low cost is very important, the LM2742 can

also be used as an asynchronous controller, as shown in the

above circuit. Although a a schottky diode in place of the bot-

tom FET will not be as efficient, it will cost much less than the

FET. The 5V at low current needed to run the LM2742 could

come from a zener diode or inexpensive regulator, such as

the one shown in Figure 8. Because the LM2742 senses cur-

rent in the low side MOSFET, the current limit feature will not

function in an asynchronous design. The ISEN pin should be

left open in this case.

17 www.national.com

LM2742

TABLE 1. Bill of Materials for Typical Application Circuit

ID Part Number Type Size Parameters Qty. Vendor

U1 LM2742 Synchronous

Controller TSSOP-14 TSSOP-14 1 NSC

Q1, Q2 Si4884DY N-MOSFET SO-8 30V, 13mΩ, 15nC 1 Vishay

L1 RLF7030T-1R5N6R1 Inductor 7.1x7.1x3.2mm 1.5µH, 6.1A 9.6mΩ1 TDK

Cin1, Cin2 C2012X5R1J106M MLCC 0805 10µF 6.3V 2 TDK

Cinx C3216X7R1E105K Capacitor 1206 1µF, 25V 1 TDK

Co1, Co2 6MV2200WG AL-E 10mm D 20mm H 2200µF 6.3V125mΩ2 Sanyo

Cboot VJ1206X104XXA Capacitor 1206 0.1µF, 25V 1 Vishay

Cin C3216X7R1E225K Capacitor 1206 2.2µF, 25V 1 TDK

Css VJ1206X123KXX Capacitor 1206 12nF, 25V 1 Vishay

Cc1 VJ1206A2R2KXX Capacitor 1206 2.2pF 10% 1 Vishay

Cc2 VJ1206A181KXX Capacitor 1206 180pF 10% 1 Vishay

Rin CRCW1206100J Resistor 1206 10Ω 5% 1 Vishay

Rfadj CRCW12066342F Resistor 1206 63.4kΩ 1% 1 Vishay

Rc1 CRCW12063923F Resistor 1206 392kΩ 1% 1 Vishay

Rfb1 CRCW12061002F Resistor 1206 10kΩ 1% 1 Vishay

Rfb2 CRCW12061002F Resistor 1206 10kΩ 1% 1 Vishay

Rcs CRCW1206222J Resistor 1206 2.2kΩ 5% 1 Vishay

TABLE 2. Bill of Materials for Circuit of Figure 3

(Identical to BOM for 1.5V except as noted below)

ID Part Number Type Size Parameters Qty. Vendor

L1 RLF12560T-2R7N110 Inductor 12.5x12.8x6mm 2.7µH, 14.4A 4.5mΩ1 TDK

Co1, Co2,

Co3, Co4 10TPB100M POSCAP 7.3x4.3x2.8mm 100µF 10V 1.9Arms 4 Sanyo

Cc1 VJ1206A6R8KXX Capacitor 1206 6.8pF 10% 1 Vishay

Cc2 VJ1206A271KXX Capacitor 1206 270pF 10% 1 Vishay

Cc3 VJ1206A471KXX Capacitor 1206 470pF 10% 1 Vishay

Rc2 CRCW12068451F Resistor 1206 8.45kΩ 1% 1 Vishay

Rfb1 CRCW12061102F Resistor 1206 11kΩ 1% 1 Vishay

TABLE 3. Bill of Materials for Circuit of Figure 4

ID Part Number Type Size Parameters Qty. Vendor

U1 LM2742 Synchronous

Controller TSSOP-14 1 NSC

Q1 Si4442DY N-MOSFET SO-8 30V, 4.1mΩ, @ 4.5V, 36nC 1 Vishay

Q2 Si4442DY N-MOSFET SO-8 30V, 4.1mΩ, @ 4.5V, 36nC 1 Vishay

D1 BAT-54 Schottky Diode SOT-23 30V 1 Vishay

Lin SLF12575T-1R2N8R2 Inductor 12.5x12.5x7.5mm 12µH, 8.2A, 6.9mΩ1 Coilcraft

L1 D05022-152HC Inductor 22.35x16.26x8mm 1.5µH, 15A,4mΩ1 Coilcraft

Cin1, Cin2 10MV5600AX Aluminum

Electrolytic 16mm D 25mm H 5600µF10V 2.35Arms 2 Sanyo

Cinx C3216X7R1E105K Capacitor 1206 1µF, 25V 1 TDK

Co1, Co2,

Co3 10MV5600AX Aluminum

Electrolytic 16mm D 25mm H 5600µF10V 2.35Arms 2 Sanyo

Cboot VJ1206X104XXA Capacitor 1206 0.1µF, 25V 1 Vishay

Cin C3216X7R1E225K Capacitor 1206 2.2µF, 25V 1 TDK

Css VJ1206X123KXX Capacitor 1206 12nF, 25V 1 Vishay

www.national.com 18

LM2742

ID Part Number Type Size Parameters Qty. Vendor

Cc1 VJ1206A4R7KXX Capacitor 1206 4.7pF 10% 1 Vishay

Cc2 VJ1206A102KXX Capacitor 1206 1nF 10% 1 Vishay

Rin CRCW1206100J Resistor 1206 10Ω 5% 1 Vishay

Rfadj CRCW12068872F Resistor 1206 88.7kΩ 1% 1 Vishay

Rc1 CRCW12062293F Resistor 1206 229kΩ 1% 1 Vishay

Rfb1 CRCW12064991F Resistor 1206 4.99kΩ 1% 1 Vishay

Rfb2 CRCW12064991F Resistor 1206 4.99kΩ 1% 1 Vishay

Rcs CRCW1206152J Resistor 1206 1.5kΩ 5% 1 Vishay

TABLE 4. Bill of Materials for Circuit of Figure 5

ID Part Number Type Size Parameters Qty. Vendor

U1 LM2742 Synchronous

Controller

TSSOP-14 1 NSC

Q1/Q2 Si4826DY Asymetric Dual

N-MOSFET

SO-8 30V, 24mΩ/ 8nC

Top 16.5mΩ/ 15nC

1 Vishay

L1 DO3316P-222 Inductor 12.95x9.4x 5.21mm 2.2µH, 6.1A, 12mΩ1 Coilcraft

Cin1 10TPB100ML POSCAP 7.3x4.3x3.1mm 100µF 10V 1.9Arms 1 Sanyo

Co1 4TPB220ML POSCAP 7.3x4.3x3.1mm 220µF 4V 1.9Arms 1 Sanyo

Cc C3216X7R1E105K Capacitor 1206 1µF, 25V 1 TDK

Cin C3216X7R1E225K Capacitor 1206 2.2µF, 25V 1 TDK

Css VJ1206X123KXX Capacitor 1206 12nF, 25V 1 Vishay

Cc1 VJ1206A100KXX Capacitor 1206 10pF 10% 1 Vishay

Cc2 VJ1206A561KXX Capacitor 1206 560pF 10% 1 Vishay

Rin CRCW1206100J Resistor 1206 10Ω 5% 1 Vishay

Rfadj CRCW12064222F Resistor 1206 42.2kΩ 1% 1 Vishay

Rc1 CRCW12065112F Resistor 1206 51.1kΩ 1% 1 Vishay

Rfb1 CRCW12062491F Resistor 1206 2.49kΩ 1% 1 Vishay

Rfb2 CRCW12064991F Resistor 1206 4.99kΩ 1% 1 Vishay

Rcs CRCW1206272J Resistor 1206 2.7kΩ 5% 1 Vishay

TABLE 5. Bill of Materials for Circuit of Figure 6

ID Part Number Type Size Parameters Qty. Vendor

U1 LM2742 Synchronous

Controller

TSSOP-14 1 NSC

Q1 Si4884DY N-MOSFET SO-8 30V, 13.5mΩ, @ 4.5V

15.3nC

1 Vishay

Q2 Si4884DY N-MOSFET SO-8 30V, 13.5mΩ, @ 4.5V

15.3nC

1 Vishay

D1 BAT-54 Schottky Diode SOT-23 30V 1 Vishay

Lin P1166.102T Inductor 7.29x7.29 3.51mm 1µH, 11A 3.7mΩ1 Pulse

L1 P1168.102T Inductor 12x12x4.5 mm 1µH, 11A, 3.7mΩ1 Pulse

Cin1 10MV5600AX Aluminum

Electrolytic

16mm D 25mm H 5600µF 10V 2.35Arms 1 Sanyo

Cinx C3216X7R1E105K Capacitor 1206 1µF, 25V 1 TDK

Co1, Co2,

Co3

16MV4700WX Aluminum

Electrolytic

12.5mm D 30mm H 4700µF 16V 2.8Arms 2 Sanyo

Cboot VJ1206X104XXA Capacitor 1206 0.1µF, 25V 1 Vishay

Cin C3216X7R1E225K Capacitor 1206 2.2µF, 25V 1 TDK

Css VJ1206X123KXX Capacitor 1206 12nF, 25V 1 Vishay

19 www.national.com

LM2742

ID Part Number Type Size Parameters Qty. Vendor

Cc1 VJ1206A4R7KXX Capacitor 1206 4.7pF 10% 1 Vishay

Cc2 VJ1206A681KXX Capacitor 1206 680pF 10% 1 Vishay

Rin CRCW1206100J Resistor 1206 10Ω 5% 1 Vishay

Rfadj CRCW12064992F Resistor 1206 49.9kΩ 1% 1 Vishay

Rc1 CRCW12061473F Resistor 1206 147kΩ 1% 1 Vishay

Rfb1 CRCW12061492F Resistor 1206 14.9kΩ 1% 1 Vishay

Rfb2 CRCW12064991F Resistor 1206 4.99kΩ 1% 1 Vishay

Rcs CRCW1206332J Resistor 1206 3.3kΩ 5% 1 Vishay

TABLE 6. Bill of Materials for Circuit of Figure 7

ID Part Number Type Size Parameters Qty. Vendor

U1 LM2742 Synchronous

Controller

TSSOP-14 1 NSC

Q1/Q2 Si4826DY Assymetric Dual

N-MOSFET

SO-8 30V, 24mΩ/ 8nC

Top 16.5mΩ/ 15nC

1 Vishay

D1 BAT-54 Schottky Diode SOT-23 30V 1 Vishay

Lin RLF7030T-1R0N64 Inductor 6.8x7.1x3.2mm 1µH, 6.4A, 7.3mΩ1 TDK

L1 RLF7030T-3R3M4R1 Inductor 6.8x7.1x3.2mm 3.3µH, 4.1A, 17.4mΩ1 TDK

Cin1 C4532X5R1E156M MLCC 1812 15µF 25V 3.3Arms 1 Sanyo

Co1 C4532X5R1E156M MLCC 1812 15µF 25V 3.3Arms 1 Sanyo

Cboot VJ1206X104XXA Capacitor 1206 0.1µF, 25V 1 TDK

Cin C3216X7R1E225K Capacitor 1206 2.2µF, 25V 1 TDK

Css VJ1206X393KXX Capacitor 1206 39nF, 25V 1 Vishay

Cc1 VJ1206A220KXX Capacitor 1206 22pF 10% 1 Vishay

Cc2 VJ1206A681KXX Capacitor 1206 680pF 10% 1 Vishay

Cc3 VJ1206A681KXX Capacitor 1206 680pF 10% 1 Vishay

Rin CRCW1206100J Resistor 1206 10Ω 5% 1 Vishay

Rfadj CRCW12061742F Resistor 1206 17.4kΩ 1% 1 Vishay

Rc1 CRCW12061072F Resistor 1206 10.7kΩ 1% 1 Vishay

Rc2 CRCW120666R5F Resistor 1206 66.5Ω 1% 1 Vishay

Rfb1 CRCW12064991F Resistor 1206 4.99kΩ 1% 1 Vishay

Rfb2 CRCW12061002F Resistor 1206 10kΩ 1% 1 Vishay

Rcs CRCW1206152J Resistor 1206 1.5kΩ 5% 1 Vishay

TABLE 7. Bill of Materials for 3.3V Circuit of Figure 7

(Identical to BOM for 1.8V except as noted below)

ID Part Number Type Size Parameters Qty. Vendor

L1 RLF7030T-4R7M3R4 Inductor 6.8x7.1x 3.2mm 4.7µH, 3.4A, 26mΩ1 TDK

Cc1 VJ1206A270KXX Capacitor 1206 27pF 10% 1 Vishay

Cc2 VJ1206X102KXX Capacitor 1206 1nF 10% 1 Vishay

Cc3 VJ1206A821KXX Capacitor 1206 820pF 10% 1 Vishay

Rc1 CRCW12061212F Resistor 1206 12.1kΩ 1% 1 Vishay

Rc2 CRCW12054R9F Resistor 1206 54.9Ω 1% 1 Vishay

Rfb1 CRCW12062211F Resistor 1206 2.21kΩ 1% 1 Vishay

Rfb2 CRCW12061002F Resistor 1206 10kΩ 1% 1 Vishay

www.national.com 20

LM2742

TABLE 8. Bill of Materials for Circuit of Figure 8

ID Part Number Type Size Parameters Qty. Vendor

U1 LM2742 Synchronous

Controller

TSSOP-14 1 NSC

U2 LM78L05 Voltage

Regulator

SO-8 1 NSC

Q1/Q2 Si4826DY Assymetric Dual

N-MOSFET

SO-8 30V, 24mΩ/ 8nC

Top 16.5mΩ/ 15nC

1 Vishay

D1 BAT-54 Schottky Diode SOT-23 30V 1 Vishay

Lin RLF7030T-1R0N64 Inductor 6.8x7.1x3.2mm 1µH, 6.4A, 7.3mΩ1 TDK

L1 SLF12565T-4R2N5R5 Inductor 12.5x12.5x6.5mm 4.2µH, 5.5A, 15mΩ1 TDK

Cin1 16MV680WG Al-E D: 10mm L: 12.5mm 680µF 16V 3.4Arms 1 Sanyo

Cinx C3216X5R1C106M MLCC 1210 10µF 16V 3.4Arms 1 TDK

Co1 Co2 16MV680WG MLCC 1812 15µF 25V 3.3Arms 1 Sanyo

Cox C3216X5R10J06M MLCC 1206 10µF 6.3V 2.7A TDK

Cboot VJ1206X104XXA Capacitor 1206 0.1µF, 25V 1 Vishay

Cin C3216X7R1E225K Capacitor 1206 2.2µF, 25V 1 TDK

Css VJ1206X123KXX Capacitor 1206 12nF, 25V 1 Vishay

Cc1 VJ1206A8R2KXX Capacitor 1206 8.2pF 10% 1 Vishay

Cc2 VJ1206X102KXX Capacitor 1206 1nF 10% 1 Vishay

Cc3 VJ1206X472KXX Capacitor 1206 4.7nF 10% 1 Vishay

Rfadj CRCW12063252F Resistor 1206 32.5kΩ 1% 1 Vishay

Rc1 CRCW12065232F Resistor 1206 52.3kΩ 1% 1 Vishay

Rc2 CRCW120662371F Resistor 1206 2.37Ω 1% 1 Vishay

Rfb1 CRCW12062211F Resistor 1206 2.21kΩ 1% 1 Vishay

Rfb2 CRCW12061002F Resistor 1206 10kΩ 1% 1 Vishay

Rcs CRCW1206202J Resistor 1206 2kΩ 5% 1 Vishay

TABLE 9. Bill of Materials for Circuit of Figure 9

ID Part Number Type Size Parameters Qty. Vendor

U1 LM2742 Synchronous

Controller

TSSOP-14 1 NSC

Q1 Si4894DY N-MOSFET SO-8 30V, 15mΩ, 11.5nC 1 Vishay

D2 MBRS330T3 Schottky Diode SO-8 30V, 3A 1 ON

L1 SLF12565T-470M2R4 Inductor 12.5x12.8x 4.7mm 47µH, 2.7A 53mΩ1 TDK

D1 MBR0520 Schottky Diode 1812 20V 0.5A 1 ON

Cin1 16MV680WG Al-E 1206 680µF, 16V, 1.54Arms 1 Sanyo

Cinx C3216X5R1C106M MLCC 1206 10µF, 16V, 3.4Arms 1 TDK

Co1, Co2 16MV680WG Al-E D: 10mm L: 12.5mm 680µF 16V 26mΩ2 Sanyo

Cox C3216X5R10J06M MLCC 1206 10µF, 6.3V 2.7A 1 TDK

Cboot VJ1206X104XXA Capacitor 1206 0.1µF, 25V 1 Vishay

Cin C3216X7R1E225K Capacitor 1206 2.2µF, 25V 1 TDK

Css VJ1206X123KXX Capacitor 1206 12nF, 25V 1 Vishay

Cc1 VJ1206A561KXX Capacitor 1206 56pF 10% 1 Vishay

Cc2 VJ1206X392KXX Capacitor 1206 3.9nF 10% 1 Vishay

Cc3 VJ1206X223KXX Capacitor 1206 22nF 10% 1 Vishay

Rfadj CRCW12062673F Resistor 1206 267kΩ 1% 1 Vishay

Rc1 CRCW12066192F Resistor 1206 61.9kΩ 1% 1 Vishay

Rc2 CRCW12067503F Resistor 1206 750kΩ 1% 1 Vishay

Rfb1 CRCW12061371F Resistor 1206 1.37kΩ 1% 1 Vishay

21 www.national.com

LM2742

ID Part Number Type Size Parameters Qty. Vendor

Rfb2 CRCW12061002F Resistor 1206 10kΩ 1% 1 Vishay

Rcs CRCW1206122F Resistor 1206 1.2kΩ 5% 1 Vishay

www.national.com 22

LM2742

Physical Dimensions inches (millimeters) unless otherwise noted

TSSOP-14 Pin Package

NS Package Number MTC14

23 www.national.com

LM2742

Notes

LM2742 N-Channel FET Synchronous Buck Regulator Controller for Low Output Voltages

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