LinearTechnologyChronicle A Showcase of Linear Technology's Focus Products February 2001 Product of the Month Tiny Step-Down Switching Regulators Operate at Megahertz Speeds--LTC1779/LT1616/LTC1701 Part 2: New Current Mode Regulators in SOT-23 New miniature high frequency switching regulators greatly expand the options available to designers of portable and communications products. Three of these new products are supplied in the tiny SOT-23 package. (See Part 1 in the January issue for similar devices in MSOP packages.) These current mode devices deliver fast transient response and excellent loop stability. Each operate at high frequency for very low ripple in sensitive bands and for tiny, low cost, surface mount inductors and capacitors. They each function at high duty cycles (Table 1) for low dropout operation that extends battery run time in portable systems. Two of the devices use Burst ModeTM operation for ultralow power consumption when the converter has very low load. LTC is now converting its SOT-23 packages from a maximum height of 1.45mm to 1.0mm. LTC1779 250mA, 94% Efficiency, Output as Low as 0.8V The constant frequency, 500kHz LTC(R)1779 includes a 250mA MOSFET switch on-board. The input voltage range of 2.5V to 9.8V enables 1-cell and 2-cell lithium-ion conversions to outputs as low as Table 1. New High Frequency, Current Mode Step-Down Switching Regulators in SOT-23 LTC1779 LT1616 LTC1701* LTC1701B 250mA 450mA 500mA 500mA 2.5V to 9.8V 3.6V to 25V 2.5V to 5.5V 2.5V to 5.5V 550kHz** 1.4MHz** 1MHz 1MHz 94% 85% 94% 94% VREF (Min VOUT) 0.8V 1.25V 1.25V 1.25V Supply Current IQ 135A 1.9mA 135A 185A IOUT Maximum Input Range Switching Frequency Efficiency Burst Mode Operation ISHUTDOWN Max Duty Cycle Package 8A <1A 1A 1A 100% 80% 100% 100% SOT-23 SOT-23 SOT-23 SOT-23 *Introduced October 1999 **Constant frequency devices Peak, 3.3V to 2.5V conversion (5V to 3.3V for LT1616) Inside This Issue: Fast Settling, True 16-Bit Voltage Output DAC Includes Precision 4-Quadrant Resistors On-Chip--LTC1821 ............................................................. 2 FET Input, Fast, High Gain Photodiode Amplifier Using the LT1806 ...................................... 3 Revised SOT-23 Packages are Thinner ................................................................................. 3 Linear Technology Chronicle * February 2001 Vol. 10 No. 2 0.8V (Figure 1). The high frequency allows the use of a small, low height inductor. Applications include portable products, power supplies for ARMs, RISC processors and distributed battery systems. An accurate undervoltage lockout shuts down the LTC1779 when the input voltage falls below 2V. For further protection, the overvoltage comparator in the LTC1779 will turn the internal MOSFET off when the feedback voltage has risen 7.5% above the reference voltage of 0.8V. The LTC1779 consumes only 135A of quiescent current to maximize battery life. In shutdown, the device draws only 8A. For applications where efficiency at light loads is a prime consideration, the LTC1779 is configured for Burst Mode operation. Continued on page 2 High Speed, Rail-to-Rail Op Amps Provide High Performance On 3V Supplies--LT1806/LT1807 and LT1809/LT1810 The LT(R)1806/LT1807 are single and dual rail-to-rail op amps optimized for use in low noise, high performance communications systems. In addition to a low voltage noise of 3.5nV/Hz , these amplifiers feature a 325MHz gain-bandwidth product, a 140V/s slew rate and an 85mA output current. The 325MHz gain bandwidth and low THD of -80dBc at 5MHz assures high performance at low supply voltages. The unique combination of low voltage operation, wide bandwidth, low THD and low noise makes the LT1806/LT1807 the perfect op amps in a wide variety of applications, such as broadband digital communications, high speed data acquisition and high performance video applications (see Figure 1). Continued on page 4 , LTC and LT are registered trademarks of Linear Technology Corporation. Burst Mode and OPTI-LOOP are trademarks of Linear Technology Corporation. 1 LTC1779/LT1616/LTC1701 from page 1 LT1616: 600mA, 1.4MHz Fixed Frequency, Inputs up to 25V The LT1616 regulates a wide range of power sources with voltages of 3.6V to 25V such as 4-cell battery packs, 5V logic rails, unregulated wall adapters and lead-acid batteries. The 1.4MHz switching frequency keeps switching noise well above the passband of most communication systems. The LT1616 remains in fixed frequency mode even with light loads for systems needing the lowest noise. The complete LT1616 regulator footprint occupies less than 0.15in2 (1cm2). Its 600mA internal switch eliminates the need for an external MOSFET and a sense resistor (Figure 2). High efficiency, up to 85%, reduces thermal dissipation compared to other DC/DC converters. The shutdown mode consumes very low current (less than 1A) and completely disconnects the output for easy power management. Built-in current limiting protects against shorted outputs. LTC1701/LTC1701B: 500mA Regulators Switch at 1MHz The LTC1701 accepts inputs of 2.5V to 5.5V (6V maximum) for long life in single-cell Li-Ion or 3-/4-cell NiCd/NiMH battery systems. The area used by the complete regulator is less than 0.3in2 (2cm2). The LTC1701 may also be configured as a zeta converter for step-up/step-down applications. The output voltage is adjustable from 1.25V to 5V. The built-in 0.28 switch furnishes up to 500mA of output current at 94% efficiency. LTC's unique OPTI-LOOPTM 1 20k 2 SW ITH/RUN LTC1779 GND VIN + VFB SENSE - D1 5 100pF 3 L1 22H 6 4 VIN 2.5V TO 9.8V C1 10F 16V C3 0.1F compensation enables fast transient response. Automatic Burst Mode operation maintains high efficiency at low output currents by reducing the switching losses. With no load, the converter draws only 135A; in shutdown, it requires less than 1A. The low cost and low ESR of ceramic capacitors make them attractive for use in switching regulators. However, ceramic capacitors are prone to changes with temperature and their ESR is so low that they cause loop-stability problems. OPTI-LOOP compensation in the LTC1701 facilitates its use in an all ceramic capacitor design. The new LTC1701B version switches continuously at 1MHz even with very low loads for the lowest ripple and noise. The quiescent current for this version is 185A. 5 VIN 4.5V TO 25V VIN D2 1 BOOST C3 L1 0.01F 10H LT1616 C2 47F 6V 169k VOUT 2.5V 100mA 4 OFF ON SHDN SW GND FB 2 R1 10 1779 F01a R1 16.5k 3 C1 1F 78.7k 6 D1 C2 10F R2 10k C1: TAIYO-YUDEN TMK316BJ105 C2: TAIYO-YUDEN JMK316BJ106ML D1: ON SEMICONDUCTOR MBR0530 D2: 1N4148 L1: SUMIDA CR43-100 C1: TAIYO YUDEN CERAMIC EMK325BJ106MNT C2: SANYO POSCAP 6TPA47M D1: IR10BQ015 L1: COILTRONICS UP1B220 Figure 1. LTC1779 High Efficiency 2.5V/100mA Step-Down Converter VOUT 3.3V 300mA: VIN = 4.5V TO 25V 400mA: VIN = 4.7V TO 20V 1616 TA01 Figure 2. LT1616 Step-Down Converter, 3.3V Output Fast Settling, True 16-Bit Voltage Output DAC Includes Precision 4-Quadrant Resistors On-Chip--LTC1821 The LTC1821 is the industry's first voltage output DAC to offer true 16-bit linearity over the industrial temperature range as well as 2s settling time for precision applications. This combination of precision performance and 16-bit accuracy makes it suitable for digital waveform generation as well as data acquisition, automatic test equipment, process control and industrial automation. The LTC1821 comes in two 16-bit monotonic grades. The A grade offers 1LSB INL whereas the B grade offers 2LSB INL, both over industrial and commercial temperature ranges. 4-quadrant multiplication is achieved with on-chip 4-quadrant multiplication resistors. These on-chip resistors simplify the connection to an external op amp for multiplying the reference input and configuring the analog output for unipolar or bipolar VREF -VREF 3 2 + - 5V 0.1F 6 LT1468 15pF 15pF 10 R1 9 RCOM 8 REF 2 VCC 11 ROFS 12 14 RFB IOUT V+ R1 ROFS R2 16 DATA INPUTS LTC1821-1 RFB 13 16-BIT DAC + WR LD CLR VOUT V- 24 23 7 DNC* DNC* DNC* NC 18 19 21 22 15V 0.1F - 3 TO 6, 25 TO 36 WR LD CLR 15 DGND 1 20 VREF VOUT = -VREF -15V 0.1F AGNDF AGNDS 17 16 1821 TA01 *DO NOT CONNECT Figure 1. LTC1821 Block Diagram Continued on page 3 Contact your local Linear Technology sales office for a data sheet and evaluation samples. For more information, visit our web site at www.linear-tech.com. 2 Linear Technology Chronicle * February 2001 Application of the Month FET Input, Fast, High Gain Photodiode Amplifier Using the LT1806 The LT1806 is a low noise rail-to-rail input and output unity-gain stable op amp that features a 325MHz gain bandwidth product, a 140V/s slew rate and an 85mA output current. It is optimized for low voltage, high performance signal conditioning systems. Figure 1 shows a fast, high gain transimpedance amplifier applied to a photodiode. A JFET buffer is used for its extremely low input bias current and high speed. The LT1097 and 2N3904 keep the JFET biased at IDSS for zero offset and lowest voltage noise. The JFET then drives the LT1806, with RF closing the high speed loop back to the JFET input and setting the transimpedance gain. C4 helps improve the phase margin of the fast loop. Output voltage noise density was measured as 9nV/Hz with RF short circuited. With RF varied from 100k to 1M, total output noise was below 1mVRMS measured over a 10MHz bandwidth. Table 1 shows results achieved with various values of RF and Figure 2 shows the time domain response with RF = 499k. VS+ -3dB BANDWIDTH 100k 64ns 6.8MHz 200k 94ns 4.6MHz 499k 154ns 3MHz 1M 263ns 1.8MHz VS+ R2 1M VS- VS+ + - 2 7 - LT1806 C1 100pF 3 7 LT1097 2 10% TO 90% RISE TIME C4 3pF * R1 10M 3 RF RF 2N5486 SIEMENS/ INFINEON SFH213FA PHOTODIODE Table 1. Results Achieved for Various RF, 1.2V Output Step + 6 6 49.9 VOUT 50 4 VS- 100mV/DIV 18067 F10 R3 10k 4 C2 2200pF VS- 2N3904 C3 0.1F R4 2.4k *ADJUST PARASITIC CAPACITANCE AT RF FOR DESIRED RESPONSE CHARACTERISTICS VS = 5V R5 33 VS- 100mV/DIV 18067 F11 Figure 2. Step Response with RF = 499k Figure 1. Fast, High Gain Photodiode Amplifier LTC1821 from page 2 1.0 Revised SOT-23 Packages are Thinner VREF = 10V VOUT = 10V BIPOLAR 0.8 INTEGRAL NONLINEARITY (LSB) ranges. The resistor connections allow 0V to 10V, 0V to -10V or 10V output ranges with 15V supplies. An asynchronous clear pin resets the LTC1821 to zero scale while the LTC1821-1 is reset to midscale allowing bipolar applications to reset to zero volts. The LTC1821 and LTC1821-1, both A and B versions, are available in the commercial and industrial temperature ranges. All versions of the LTC1821 devices are packaged in the 36-pin SSOP package, providing a much smaller design than comparable parallel input DACs. 0.6 0.4 0.2 0 -0.2 -0.4 -0.6 -0.8 -1.0 0 49152 32768 16384 DIGITAL INPUT CODE 65535 1821 TA02 LTC1821/LTC1821-1 Integral Nonlinearity LTC is putting into production as of January 2001, revised 5-lead and 6-lead SOT-23 packages that are thinner in height. This change is in response to customer desires to make even thinner circuits. The previous maximum thickness (height from the board) was 1.45mm. The revised maximum height is 1.0mm. The revised packages will be used on new builds of all products that are supplied in these packages. Shipments of products in the revised packages will begin Spring 2001. Contact your sales office or distributor for details. Contact your local Linear Technology sales office for a data sheet and evaluation samples. For more information, visit our web site at www.linear-tech.com. Linear Technology Chronicle * February 2001 3 LT1806/LT1807 and LT1809/LT1810 from page 1 In addition to the low voltage low noise performance, the overall DC precision of these high speed op amps is unmatched by any competitive device. A maximum offset voltage of less than 0.5mV, CMRR of 106dB and a large-signal voltage gain of 300V/mV dispel any concerns about low voltage operation. The LT1806/LT1807 have an input range that includes both supply rails and an output that swings within 20mV of either supply rail to maximize the signal dynamic range in low supply applications. The LT1806/LT1807 maintain their performance for supplies from 2.5V to 12.6V and are specified at 3V, 5V and 5V supplies. With the LT1806/LT1807, you can now lower your systems supplies without losing precision and bandwidth. The LT1806 is available in an 8-pin SO package with the standard op amp pinout and a 6-pin SOT-23 package. The LT1807 features the standard dual op amp pinout and is available in 8-pin SO and MSOP packages. Both parts are available in commercial and industrial temperature grades. The LT1809/LT1810 are single and dual rail-to-rail input and output op amps optimized for use in low voltage, high performance signal conditioning systems. With 180MHz gain bandwidth, 350V/s slew rate and low THD of - 90dBc up to 5MHz (see Figure 2), the LT1809/LT1810 are the first op amps designed for 3V broadband applications. A wide input common mode range that includes both rails and a rail-to-rail output stage that is guaranteed to swing within 20mV of either rail offers exceptional dynamic range. The LT1809/LT1810 maintain their performance for supplies from 2.5V to 12.6V and are specified at 3V, 5V and 5V supplies. The inputs can be driven beyond the supplies without damage or phase reversal of the output. This unique combination of low distortion, rail-to-rail input and output and low supply voltage operation makes the LT1809/ LT1810 the first op amps to support complete 3V system design of broadband communication, high performance video and high speed data acquisition systems. The LT1809 is available in the 8-pin SO package with the standard op amp pinout and the 6-pin SOT-23 package. The LT1810 features the standard dual op amp pinout and is available in 8-pin SO and MSOP packages. Both devices are available in both commercial and industrial temperature ranges. Table 1. Operating Performance for LT1806/LT1807 and LT1809/LT1810 LT1806/ LT1807 LT1809/ LT1810 Gain-Bandwidth Product 325MHz 320MHz Slew Rate 140V/s 350V/s THD - 80dBc - 90dBc Voltage Noise 3.5nV/Hz 16nV/Hz Offset Voltage 700V 3.5mV 5mA 10mA CMRR 83dB 70dB AVOL 100dB 89dB Supply Current Per Amp 16mA 20mA Bias Current + 1/2 LT1807 - R1 100 R2 909 5V R5 49.9 C1 5.6pF VIN C3 470pF C2 5.6pF +AVIN LTC1420 PGA GAIN = 1 -AVIN VREF = 4.096V 12 BITS 10Msps R6 49.9 18067 TA01 R3 100 -5V R4 1k - 1/2 LT1807 + Figure 1. Gain of 20 Differential A/D Driver Using LT1807 -40 DISTORTION (dB) -50 AV = +1 VIN = 2VP-P VS = 5V -60 -70 Linear Technology Products Are Distributed By: RL = 100, 2ND -80 -90 RL = 100, 3RD RL = 1k, 3RD -100 RL = 1k, 2ND -110 0.3 1 10 30 FREQUENCY (MHz) 1809 TA02 Arrow Electronics Arrow/Zeus Components Digi-Key Gerber Electronics Avnet Figure 2. Distortion vs Frequency for the LT1809 (c) 2001 Linear Technology Corporation/Printed in USA Contact your local Linear Technology sales office for a data sheet and evaluation samples. For more information, visit our web site at www.linear-tech.com. * www.linear-tech.com For Literature*Only: 1-800-4-LINEAR 4Linear Technology Corporation * 1630 McCarthy Blvd. * Milpitas, CA 95035-7417 * (408) 432-1900 * FAX: (408) 434-0507Linear Technology *Chronicle February 2001