REV. D
Information furnished by Analog Devices is believed to be accurate and
reliable. However, no responsibility is assumed by Analog Devices for its
use, nor for any infringements of patents or other rights of third parties that
may result from its use. No license is granted by implication or otherwise
under any patent or patent rights of Analog Devices.
a
AD202/AD204
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 781/329-4700 www.analog.com
Fax: 781/326-8703 © Analog Devices, Inc., 2002
Low Cost, Miniature
Isolation Amplifiers
FEATURES
Small Size: 4 Channels/lnch
Low Power: 35 mW (AD204)
High Accuracy: 0.025% Max Nonlinearity (K Grade)
High CMR: 130 dB (Gain = 100 V/V)
Wide Bandwidth: 5 kHz Full-Power (AD204)
High CMV Isolation: 2000 V pk Continuous (K Grade)
(Signal and Power)
Isolated Power Outputs
Uncommitted Input Amplifier
APPLICATIONS
Multichannel Data Acquisition
Current Shunt Measurements
Motor Controls
Process Signal Isolation
High Voltage Instrumentation Amplifier
GENERAL DESCRIPTION
The AD202 and AD204 are general purpose, two-port, trans-
former-coupled isolation amplifiers that may be used in a broad
range of applications where input signals must be measured,
processed, and/or transmitted without a galvanic connection.
These industry standard isolation amplifiers offer a complete
isolation function, with both signal and power isolation provided
for in a single compact plastic SIP or DIP style package. The
primary distinction between the AD202 and the AD204 is that
the AD202 is powered directly from a 15 V dc supply while the
AD204 is powered by an externally supplied clock, such as the
recommended AD246 Clock Driver.
The AD202 and AD204 provide total galvanic isolation between
the input and output stages of the isolation amplifier through
the use of internal transformer-coupling. The functionally com-
plete AD202 and AD204 eliminate the need for an external,
user-supplied dc-to-dc converter. This permits the designer
to minimize the necessary circuit overhead and consequently
reduce the overall design and component costs.
The design of the AD202 and AD204 emphasizes maximum
flexibility and ease of use, including the availability of an
uncommitted op amp on the input stage. They feature a bipolar
±5 V output range, an adjustable gain range of from 1V/V to
100 V/V, ±0.025% max nonlinearity (K grade), 130 dB of
CMR, and the AD204 consumes a low 35 mW of power.
The functional block diagrams can be seen in Figures 1a and 1b.
PRODUCT HIGHLIGHTS
The AD202 and AD204 are full-featured isolators offering
numerous benefits to the user:
Small Size: The AD202 and AD204 are available in SIP and
DIP form packages. The SIP package is just 0.25" wide, giving
the user a channel density of four channels per inch. The isolation
barrier is positioned to maximize input to output spacing. For
applications requiring a low profile, the DIP package provides a
height of just 0.350".
High Accuracy: With a maximum nonlinearity of ±0.025%
for the AD202K/AD204K (±0.05% for the AD202J/AD204J)
and low drift over temperature, the AD202 and AD204 provide
high isolation without loss of signal integrity.
Low Power: Power consumption of 35 mW (AD204) and
75 mW (AD202) over the full signal range makes these isolators
ideal for use in applications with large channel counts or tight
power budgets.
Wide Bandwidth: The AD204’s full-power bandwidth of 5 kHz
makes it useful for wideband signals. It is also effective in appli-
cations like control loops, where limited bandwidth could result
in instability.
Excellent Common-Mode Performance: The AD202K/
AD204K provide ±2000 V pk continuous common-mode isola-
tion, while the AD202J/AD204J provide ±1000 V pk continuous
common-mode isolation. All models have a total common-mode
input capacitance of less than 5 pF inclusive of power isolation.
This results in CMR ranging from 130 dB at a gain of 100 dB to
104 dB (minimum at unity gain) and very low leakage current
(2 mA maximum).
Flexible Input: An uncommitted op amp is provided at the
input of all models. This provides buffering and gain as required,
and facilitates many alternative input functions including filtering,
summing, high voltage ranges, and current (transimpedance) input.
Isolated Power: The AD204 can supply isolated power of
±7.5 V at 2 mA. This is sufficient to operate a low-drift input
preamp, provide excitation to a semiconductor strain gage, or
power any of a wide range of user-supplied ancillary circuits.
The AD202 can supply ±7.5 V at 0.4 mA, which is sufficient to
operate adjustment networks or low power references and op
amps, or to provide an open-input alarm.
REV. D
–2–
AD202/AD204–SPECIFICATIONS
Model AD204J AD204K AD202J AD202K
GAIN
Range 1 V/V–100 V/V ***
Error ±0.5% typ (±4% max) ***
vs. Temperature ±20 ppm/∞C typ (±45 ppm/∞C max) ***
vs. Time ±50 ppm/1000 Hours ***
vs. Supply Voltage ±0.01%/V ±0.01%/V ±0.01%/V ±0.01%/V
Nonlinearity (G = 1 V/V)
1
±0.05% max ±0.025% max ±0.05% max ±0.025% max
Nonlinearity vs. Isolated Supply Load ±0.0015%/mA ***
INPUT VOLTAGE RATINGS
Input Voltage Range ±5 V ***
Max lsolation Voltage (Input to Output)
AC, 60 Hz, Continuous 750 V rms 1500 V rms 750 V rms 1500 V rms
Continuous (AC and DC) ±1000 V Peak ±2000 V Peak ±1000 V Peak ±2000 V Peak
Isolation-Mode Rejection Ratio (IMRR) @ 60 Hz
R
S
£ 100 W (HI and LO Inputs) G = 1 V/V 110 dB 110 dB 105 dB 105 dB
G = 100 V/V 130 dB ***
R
S
£ l kW (Input HI, LO, or Both) G = 1 V/V 104 dB min 104 dB min 100 dB min 100 dB min
G = 100 V/V 110 dB min ***
Leakage Current Input to Output @ 240 V rms, 60 Hz 2 mA rms max ***
INPUT IMPEDANCE
Differential (G = 1 V/V) 10
12
W***
Common-Mode 2 GW储4.5 pF ***
INPUT BIAS CURRENT
Initial, @ 25∞C±30 pA ***
vs. Temperature (0∞C to 70∞C) ±10 nA ***
INPUT DIFFERENCE CURRENT
Initial, @ 25∞C±5 pA ***
vs. Temperature (0∞C to 70∞C) ±2 nA ***
INPUT NOISE
Voltage, 0.1 Hz to 100 Hz 4 mV p-p ***
f > 200 Hz 50 nV/÷Hz ***
FREQUENCY RESPONSE
Bandwidth (V
O
£ 10 V p-p, G = 1 V–50 V/V) 5 kHz 5 kHz 2 kHz 2 kHz
Settling Time, to ±10 mV (10 V Step) 1 ms ***
OFFSET VOLTAGE (RTI)
Initial, @ 25∞C Adjustable to Zero (±15 ±15/G)mV max (±5 ± 5/G) mV max (±15 ±15/G) mV max (±5 ±5/G) mV max
vs. Temperature (0∞C to 70∞C)
±± ∞
Ê
Ë
Áˆ
¯
˜
10 10
GVCm
***
RATED OUTPUT
Voltage (Out HI to Out LO) ±5 V ***
Voltage at Out HI or Out LO (Ref. Pin 32) ±6.5 V ***
Output Resistance 3 kW3 kW7 kW7 kW
Output Ripple, 100 kHz Bandwidth 10 mV p-p ***
5 kHz Bandwidth 0.5 mV rms ***
ISOLATED POWER OUTPUT
2
Voltage, No Load ±7.5 V ***
Accuracy ±10% ***
Current 2 mA (Either Output)
3
2 mA (Either Output)
3
400 mA Total 400 mA Total
Regulation, No Load to Full Load 5% ***
Ripple 100 mV p-p ***
OSCILLATOR DRIVE INPUT
Input Voltage 15 V p-p Nominal 15 V p-p Nominal N/A N/A
Input Frequency 25 kHz Nominal 25 kHz Nominal N/A N/A
POWER SUPPLY (AD202 Only)
Voltage, Rated Performance N/A N/A 15 V ± 5% 15 V ± 5%
Voltage, Operating N/A N/A 15 V ± 10% 15 V ± 10%
Current, No Load (V
S
= 15 V) N/A N/A 5 mA 5 mA
TEMPERATURE RANGE
Rated Performance 0∞C to 70∞C***
Operating –40∞C to +85∞C***
Storage –40∞C to +85∞C***
PACKAGE DIMENSIONS
4
SIP Package (Y) 2.08" ¥ 0.250" ¥ 0.625" ***
DlP Package (N) 2.10" ¥ 0.700" ¥ 0.350" ***
(Typical @ 25C and VS = 15 V unless otherwise noted.)
NOTES
*Specifications same as AD204J.
1Nonlinearity is specified as a % deviation from a best straight line.
21.0 mF min decoupling required (see text).
33 mA with one supply loaded.
4Width is 0.25" typ, 0.26" max.
Specifications subject to change without notice.
REV. D
AD202/AD204
–3–
AD246–SPECIFICATIONS
(Typical @ 25∞C and VS = 15 V unless otherwise noted.)
Model AD246JY AD246JN
OUTPUT
l
Frequency 25 kHz Nominal *
Voltage 15 V p-p Nominal *
Fan-Out 32 Max *
POWER SUPPLY
REQUIREMENTS
Input Voltage 15 V ± 5% *
Supply Current
Unloaded 35 mA *
Each AD204 Adds 2.2 mA *
Each 1 mA Load on AD204
+V
ISO
or –V
ISO
Adds 0.7 mA *
NOTES
*Specifications the same as the AD246JY.
1
The high current drive output will not support a short to ground.
Specifications subject to change without notice.
AD246 Pin Designations
Pin (Y) Pin (N) Function
112 15 V POWER IN
21CLOCK OUTPUT
12 14 COMMON
13 24 COMMON
ORDERING GUIDE
Package Max Common-Mode Max
Model Option Voltage (Peak) Linearity
AD202JY SIP 1000 V ±0.05%
AD202KY SIP 2000 V ±0.025%
AD202JN DIP 1000 V ±0.05%
AD202KN DIP 2000 V ±0.025%
AD204JY SIP 1000 V ±0.05%
AD204KY SIP 2000 V ±0.025%
AD204JN DIP 1000 V ±0.05%
AD204KN DIP 2000 V ±0.025%
CAUTION
ESD (electrostatic discharge) sensitive device. Electrostatic charges as high as 4000 V readily
accumulate on the human body and test equipment and can discharge without detection. Although
the AD202/AD204 features proprietary ESD protection circuitry, permanent damage may occur on
devices subjected to high energy electrostatic discharges. Therefore, proper ESD precautions are
recommended to avoid performance degradation or loss of functionality.
WARNING!
ESD SENSITIVE DEVICE
PIN DESIGNATIONS
AD202/AD204 SIP Package
Pin Function
1+INPUT
2INPUT/V
ISO
COMMON
3–INPUT
4INPUT FEEDBACK
5–V
ISO
OUTPUT
6+V
ISO
OUTPUT
31 15 V POWER IN (AD202 ONLY)
32 CLOCK/POWER COMMON
33 CLOCK INPUT (AD204 ONLY)
37 OUTPUT LO
38 OUTPUT HI
AD202/AD204 DIP Package
Pin Function
1+INPUT
2INPUT/V
ISO
COMMON
3–INPUT
18 OUTPUT LO
19 OUTPUT HI
20 15 V POWER IN (AD202 ONLY)
21 CLOCK INPUT (AD204 ONLY)
22 CLOCK/POWER COMMON
36 +V
ISO
OUTPUT
37 –V
ISO
OUTPUT
38 INPUT FEEDBACK
REV. D
AD202/AD204
–4–
DIFFERENCES BETWEEN THE AD202 AND AD204
The primary distinction between the AD202 and AD204 is in
the method by which they are powered: the AD202 operates
directly from 15 V dc while the AD204 is powered by a non-
isolated externally-supplied clock (AD246) that can drive up to
32 AD204s. The main advantages of using the externally-
clocked AD204 over the AD202 are reduced cost in multichannel
applications, lower power consumption, and higher bandwidth.
In addition, the AD204 can supply substantially more isolated
power than the AD202.
Of course, in a great many situations, especially where only one
or a few isolators are used, the convenience of standalone opera-
tion provided by the AD202 will be more significant than any
of the AD204’s advantages. There may also be cases where it is
desirable to accommodate either device interchangeably, so the
pinouts of the two products have been designed to make that
easy to do.
RECT
AND
FILTER
OSCILLATOR
DEMOD
MOD
SIGNAL
POWER
ⴞ5V
FS
+7.5V
–7.5V
25kHz 25kHz
AD202
FB
IN–
IN+
IN COM
VSIG
+VISO OUT
–VISO OUT
ⴞ5V
FS
HI
LO
15V DC
POWER
RETURN
VOUT
Figure 1a. AD202 Functional Block Diagram
RECT
AND
FILTER
POWER
CONV.
DEMOD
MOD
SIGNAL
POWER
ⴞ5V
FS
+7.5V
–7.5V
25kHz 25kHz
AD204
FB
IN–
IN+
IN COM
V
SIG
+V
ISO
OUT
–V
ISO
OUT
ⴞ5V
FS
HI
LO
CLOCK
15V p-p
25kHz
POWER
RETURN
V
OUT
Figure 1b. AD204 Functional Block Diagram
(Pin Designations Apply to the DIP-Style Package)
INSIDE THE AD202 AND AD204
The AD202 and AD204 use an amplitude modulation technique
to permit transformer coupling of signals down to dc (Figure 1a
and 1b). Both models also contain an uncommitted input op
amp and a power transformer that provides isolated power to
the op amp, the modulator, and any external load. The power
transformer primary is driven by a 25 kHz, 15 V p-p square
wave generated internally in the case of the AD202, or supplied
externally for the AD204.
Within the signal swing limits of approximately ±5 V, the out-
put voltage of the isolator is equal to the output voltage of the
op amp; that is, the isolation barrier has unity gain. The output
signal is not internally buffered, so the user is free to interchange
the output leads to get signal inversion. Additionally, in multi-
channel applications, the unbuffered outputs can be multiplexed
with one buffer following the mux. This technique minimizes
offset errors while reducing power consumption and cost. The
output resistance of the isolator is typically 3 kΩ for the AD204
(7 kΩ for AD202) and varies with signal level and temperature,
so it should not be loaded (see Figure 2 for the effects of load
upon nonlinearity and gain drift). In many cases, a high imped-
ance load will be present or a following circuit such as an output
filter can serve as a buffer so that a separate buffer function will
not often be needed.
OUTPUT LOAD – M⍀
0.25
0.20
0
0 1.00.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9
0.15
0.10
0.05
–10
–8
–6
–4
–2
0
–500
–400
–300
–200
–100
0
GAIN
CHANGE
(%)
GAIN TC
CHANGE
(ppm/ⴗC)
NON-
LINEARITY
(%)
AD202 GAIN AND GAIN TC
AD202 NONLINEARITY
AD204 NONLINEARITY
AD204 GAIN AND GAIN TC
Figure 2. Effects of Output Loading
USING THE AD202 AND AD204
Powering the AD202. The AD202 requires only a single 15 V
power supply connected as shown in Figure 3a. A bypass capaci-
tor is provided in the module.
15V ⴞ5%
15V RETURN
AD202
Figure 3a.
Powering the AD204. The AD204 gets its power from an
externally supplied clock signal (a 15 V p-p square wave with a
nominal frequency of 25 kHz) as shown in Figure 3b.
15V
15V RETURN
AD204 AD204 AD204
AD246
+
Figure 3b.
(NOTE: Circuit figures shown on this page are for SIP-style packages. Refer to
Page 3 for proper DIP package pinout.)
REV. D
AD202/AD204
–5–
AD246 Clock Driver. The AD246 is a compact, inexpensive
clock driver that can be used to obtain the required clock from a
single 15 V supply. Alternatively, the circuit shown in Figure 4
(essentially an AD246) can be used. In either case, one clock
circuit can operate at least 32 AD204s at the rated minimum
supply voltage of 14.25 V and one additional isolator can be
operated for each 40 mV increase in supply voltage up to 15 V.
A supply bypass capacitor is included in the AD246, but if many
AD204s are operated from a single AD246, an external bypass
capacitor should be used with a value of at least 1 mF for every
five isolators used. Place the capacitor as close as possible to the
clock driver.
180pF
49.9k
C
RC
R
2
3
1
Q
CD
4047B
14 6 5
12 9 8 74
10 2
4
TELEDYNE
TSC426
3
1N914
1N914
6
7
5+1F
35V
15V
CLK
OUT
CLK AND
PWR COM
Figure 4. Clock Driver
Input Configurations. The AD202 and AD204 have been
designed to be very easy to use in a wide range of applications.
The basic connection for standard unity gain applications, useful
for signals up to ±5 V, is shown in Figure 5; some of the possible
variations are described below. When smaller signals must be
handled, Figure 6 shows how to achieve gain while preserving a
very high input resistance. The value of feedback resistor R
F
should be kept above 20 kW for best results. Whenever a gain of
more than five is taken, a 100 pF capacitor from FB to IN COM
is required. At lower gains this capacitor is unnecessary, but it
will not adversely affect performance if used.
OUT
HI
OUT
LO
IN–
IN+
IN COM
15V OR
CLOCK
AD202
OR
AD204
V
OUT
5V
2k
(SEE TEXT)
V
SIG
(5V)
FB
Figure 5. Basic Unity-Gain Application
AD202
OR
AD204
2k
V
SIG
V
O
V
O
= V
SIG
1 + –––
R
F
20k
R
F
R
G
R
F
R
G
100pF
()
Figure 6. Input Connections for Gain > 1
The noninverting circuit of Figures 5 and 6 can also be used to
your advantage when a signal inversion is needed: just interchange
either the input leads or the output leads to get inversion. This
approach retains the high input resistance of the noninverting
circuit, and at unity gain no gain-setting resistors are needed.
When the isolator is not powered, a negative input voltage of
more than about 2 V will cause an input current to flow. If the
signal source can supply more than a few mA under such con-
ditions, the 2 kW resistor shown in series with IN+ should be
used to limit current to a safe value. This is particularly impor-
tant with the AD202, which may not start if a large input current
is present.
Figure 7 shows how to accommodate current inputs or sum
currents or voltages. This circuit can also be used when the
input signal is larger than the ±5 V input range of the isolator;
for example, a ±50 V input span can be accommodated with
R
F
= 20 kW and R
S
= 200 kW. Once again, a capacitor from FB
to IN COM is required for gains above five.
AD202
OR
AD204
R
S2
V
V = – (VS1 ––– + VS2 ––– + IS RF + ...)
RF 20k
RF
RS1
RF
RS2
RF
RS1
IS
VS1
VS2
Figure 7. Connections for Summing or Current Inputs
(NOTE: Circuit figures shown on this page are for SIP-style packages. Refer to
Page 3 for proper DIP package pinout.)
REV. D
AD202/AD204
–6–
Adjustments. When gain and zero adjustments are needed, the
circuit details will depend on whether adjustments are to be made
at the isolator input or output, and (for input adjustments) on
the input circuit used. Adjustments are usually best done on the
input side, because it is better to null the zero ahead of the gain,
and because gain adjustment is most easily done as part of the
gain-setting network. Input adjustments are also to be preferred
when the pots will be near the input end of the isolator (to mini-
mize common-mode strays). Adjustments on the output side
might be used if pots on the input side would represent a hazard
due to the presence of large common-mode voltages during
adjustment.
Figure 8a shows the input-side adjustment connections for use
with the noninverting connection of the input amplifier. The
zero adjustment circuit injects a small adjustment voltage in series
with the low side of the signal source. (This will not work if the
source has another current path to input common or if current
flows in the signal source LO lead). Since the adjustment volt-
age is injected ahead of the gain, the values shown will work for
any gain. Keep the resistance in series with input LO below a
few hundred ohms to avoid CMR degradation.
AD202
OR
AD204
47.5k
VS
5k
GAIN
RG
200+7.5
–7.5
100k
ZERO
2k
50k
Figure 8a. Adjustments for Noninverting Connection of
Op Amp
Also shown in Figure 8a is the preferred means of adjusting the
gain-setting network. The circuit shown gives a nominal R
F
of
50 kW, and will work properly for gains of ten or greater. The
adjustment becomes less effective at lower gains (its effect is
halved at G = 2) so that the pot will have to be a larger fraction
of the total R
F
at low gain. At G = 1 (follower) the gain cannot
be adjusted downward without compromising input resistance;
it is better to adjust gain at the signal source or after the output.
Figure 8b shows adjustments for use with inverting input cir-
cuits. The zero adjustment nulls the voltage at the summing
node. This method is preferable to current injection because it is
less affected by subsequent gain adjustment. Gain adjustment is
again done in the feedback; but in this case it will work all the
way down to unity gain (and below) without alteration.
AD202
OR
AD204
R
S
47.5k
V
S
5k
GAIN
200
50k+7.5
–7.5
100k
ZERO
Figure 8b. Adjustments for Summing or Current Input
Figure 9 shows how zero adjustment is done at the output by
taking advantage of the semi-floating output port. The range of
this adjustment will have to be increased at higher gains; if that
is done, be sure to use a suitably stable supply voltage for the
pot circuit.
There is no easy way to adjust gain at the output side of the
isolator itself. If gain adjustment must be done on the output
side, it will have to be in a following circuit such as an output
buffer or filter.
AD202
OR
AD204
200
50k100k
ZERO
0.1F
+15V
–15V
V
O
Figure 9. Output-Side Zero Adjustment
Common-Mode Performance. Figures 10a and 10b show
how the common-mode rejection of the AD202 and AD204
varies with frequency, gain, and source resistance. For these
isolators, the significant resistance will normally be that in the
path from the source of the common-mode signal to IN COM.
The AD202 and AD204 also perform well in applications re-
quiring rejection of fast common-mode steps, as described in
the Applications section.
FREQUENCY – Hz
180
10
CMR – dB
160
140
120
100
80
60
40
20 50 60 100 200 500 1k 2k 5k
G = 100
G = 1
R
LO
= 10k
R
LO
= 500
R
LO
= 0
R
LO
= 0
R
LO
= 10k
Figure 10a. AD204
(NOTE: Circuit figures shown on this page are for SIP-style packages. Refer to
Page 3 for proper DIP package pinout.)
REV. D
AD202/AD204
–7–
FREQUENCY – Hz
180
10
CMR – dB
160
140
120
100
80
60
40
20 50 60 100 200 500 1k 2k 5k
G = 100
G = 1
R
LO
= 10k
R
LO
= 500
RLO = 0
RLO = 0
R
LO
= 10k
Figure 10b. AD202
Dynamics and Noise. Frequency response plots for the AD202
and AD204 are given in Figure 11. Since neither isolator is slew-
rate limited, the plots apply for both large and small signals.
Capacitive loads of up to 470 pF will not materially affect fre-
quency response. When large signals beyond a few hundred Hz
will be present, it is advisable to bypass –V
ISO
and +V
ISO
to IN
COM with 1 mF tantalum capacitors even if the isolated supplies
are not loaded.
At 50 Hz/60 Hz, phase shift through the AD202/AD204 is typically
0.8∞ (lagging). Typical unit to unit variation is ±0.2∞ (lagging).
FREQUENCY – Hz
10
VO/VI – dB
60
–40
20 50 100 200 500 1k 2k 5k
40
20
0
–20
10k 20k
AD204
AD202
AMPLITUDE
RESPONSE
PHASE
RESPONSE
(G = 1)
0
–50
–100
PHASE DEGREES
Figure 11. Frequency Response at Several Gains
The step response of the AD204 for very fast input signals can
be improved by the use of an input filter, as shown in Figure 12.
The filter limits the bandwidth of the input (to about 5.3 kHz)
so that the isolator does not see fast, out-of-band input terms
that can cause small amounts (±0.3%) of internal ringing. The
AD204 will then settle to ±0.1% in about 300 ms for a 10 V
step.
AD204
3.3k
0.01F
VS
Figure 12. Input Filter for Improved Step Response
Except at the highest useful gains, the noise seen at the output
of the AD202 and AD204 will be almost entirely comprised of
carrier ripple at multiples of 25 kHz. The ripple is typically
2 mV p-p near zero output and increases to about 7 mV p-p for
outputs of ±5 V (1 MHz measurement bandwidth). Adding a
capacitor across the output will reduce ripple at the expense of
bandwidth: for example, 0.05 mF at the output of the AD204
will result in 1.5 mV ripple at ±5 V, but signal bandwidth will
be down to 1 kHz.
When the full isolator bandwidth is needed, the simple two-pole
active filter shown in Figure 13 can be used. It will reduce ripple
to 0.1 mV p-p with no loss of signal bandwidth, and also serves
as an output buffer.
An output buffer or filter may sometimes show output spikes
that do not appear at its input. This is usually due to clock noise
appearing at the op amp’s supply pins (since most op amps have
little or no supply rejection at high frequencies). Another com-
mon source of carrier-related noise is the sharing of a ground
track by both the output circuit and the power input. Figure 13
shows how to avoid these problems: the clock/supply port of the
isolator does not share ground or 15 V tracks with any signal
circuits, and the op amp’s supply pins are bypassed to signal
common (note that the grounded filter capacitor goes here as
well). Ideally, the output signal LO lead and the supply com-
mon meet where the isolator output is actually measured, e.g.,
at an A/D converter input. If that point is more than a few feet
from the isolator, it may be useful to bypass output LO to sup-
ply common at the isolator with a 0.1 mF capacitor.
In applications where more than a few AD204s are driven by a
single clock driver, substantial current spikes will flow in the
power return line and in whichever signal out lead returns to a
low impedance point (usually output LO). Both of these tracks
should be made large to minimize inductance and resistance;
ideally, output LO should be directly connected to a ground
plane which serves as measurement common.
Current spikes can be greatly reduced by connecting a small
inductance (68 mH–100 mH) in series with the clock pin of each
AD204. Molded chokes such as the Dale IM-2 series, with dc
resistance of about 5 W, are suitable.
AD202
OR
AD204
10k
2200pF
10k
1000pF
AD711
1.0F 1.0F
POINT OF
MEASUREMENT
AD246
(IF USED)
POWER
SUPPLY
–15V C+15V
++
Figure 13. Output Filter Circuit Showing Proper Grounding
(NOTE: Circuit figures shown on this page are for SIP-style packages. Refer to
Page 3 for proper DIP package pinout.)
REV. D
AD202/AD204
–8–
Using Isolated Power. Both the AD202 and the AD204 provide
±7.5 V power outputs referenced to input common. These may be
used to power various accessory circuits that must operate at
the input common-mode level; the input zero adjustment pots
described above are an example, and several other possible uses
are shown in the section titled Application Examples.
The isolated power output of the AD202 (400 mA total from
either or both outputs) is much more limited in current capacity
than that of the AD204, but it is sufficient for operating micro-
power op amps, low power references (such as the AD589),
adjustment circuits, and the like.
The AD204 gets its power from an external clock driver, and
can handle loads on its isolated supply outputs of 2 mA for each
supply terminal (+7.5 V and –7.5 V) or 3 mA for a single loaded
output. Whenever the external load on either supply is more
than about 200 mA, a 1 mF tantalum capacitor should be used to
bypass each loaded supply pin to input common.
Up to 32 AD204s can be driven from a single AD246 (or equi-
valent) clock driver when the isolated power outputs of the
AD204s are loaded with less than 200 mA each, at a worst-case
supply voltage of 14.25 V at the clock driver. The number of
AD204s that can be driven by one clock driver is reduced by
one AD204 per 3.5 mA of isolated power load current at 7.5 V,
distributed in any way over the AD204s being supplied by that
clock driver. Thus a load of 1.75 mA from +V
ISO
to –V
ISO
would
also count as one isolator because it spans 15 V.
It is possible to increase clock fanout by increasing supply volt-
age above the 14.25 V minimum required for 32 loads. One
additional isolator (or 3.5 mA unit load) can be driven for each
40 mV of increase in supply voltage up to 15 V. Therefore if the
minimum supply voltage can be held to 15 V – 1%, it is possible
to operate 32 AD204s and 52 mA of 7.5 V loads. Figure 14
shows the allowable combinations of load current and channel
count for various supply voltages.
MINIMUM SUPPLY VOLTAGE
14.25
NUMBER OF AD204s DRIVEN
50
0
14.50 14.75
40
30
20
10
15.0
I
ISO
= 0mA TOTAL
I
ISO
= 35mA TOTAL
I
ISO
= 70mA TOTAL
I
ISO
= 80mA
OPERATION IN THIS REGION EXCEEDS
4mA LOAD LIMIT PER AD204
TOTAL
Figure 14. AD246 Fanout Rules
Operation at Reduced Signal Swing. Although the nominal
output signal swing for the AD202 and AD204 is ±5 V, there
may be cases where a smaller signal range is desirable. When
that is done, the fixed errors (principally offset terms and output
noise) become a larger fraction of the signal, but nonlinearity is
reduced. This is shown in Figure 15.
OUTPUT SIGNAL SWING – V
0
NONLINEARITY – % span
0.025
0
23
0.020
0.015
0.010
0.005
514
Figure 15. Nonlinearity vs. Signal Swing
PCB Layout for Multichannel Applications. The pinout of
the AD204Y has been designed to make very dense packing
possible in multichannel applications. Figure 16a shows the
recommended printed circuit board (PCB) layout for the simple
voltage-follower connection. When gain-setting resistors are
present, 0.25" channel centers can still be achieved, as shown in
Figure 16b.
CHANNEL INPUTS
012
0.1”
GRID
CLK COM
CLK
OUT COM
CHANNEL OUTPUTS
TO MUX
Figure 16a.
(NOTE: Circuit figures shown on this page are for SIP-style packages. Refer to
Page 3 for proper DIP package pinout.)
REV. D
AD202/AD204
–9–
CHANNEL 0 CHANNEL 1
HI LO HI LO
R
F
R
G
R
F
R
G
100pF 100pF
0.1”
GRID
1
3
5
2
4
6
1
3
5
2
4
6
Figure 16b.
Synchronization. Since AD204s operate from a common
clock, synchronization is inherent. AD202s will normally not
interact to produce beat frequencies even when mounted on
0.25-inch centers. Interaction may occur in rare situations where
a large number of long, unshielded input cables are bundled
together and channel gains are high. In such cases, shielded
cable may be required or AD204s can be used.
APPLICATIONS EXAMPLES
Low Level Sensor Inputs. In applications where the output of
low level sensors such as thermocouples must be isolated, a low
drift input amplifier can be used with an AD204, as shown in
Figure 17. A three-pole active filter is included in the design to
get normal-mode rejection of frequencies above a few Hz and to
provide enhanced common-mode rejection at 60 Hz. If offset
adjustment is needed, it is best done at the trim pins of the OP07
itself; gain adjustment can be done at the feedback resistor.
Note that the isolated supply current is large enough to mandate
the use of 1 mF supply bypass capacitors. This circuit can be
used with an AD202 if a low power op amp is used instead of
the OP07.
Process Current Input with Offset. Figure 18 shows an
isolator receiver that translates a 4-20 mA process current
signal into a 0 V to 10 V output. A 1 V to 5 V signal appears at
the isolator’s output, and a –1 V reference applied to output LO
provides the necessary level shift (in multichannel applications,
the reference can be shared by all channels). This technique is
often useful for getting offset with a follower-type output buffer.
AD202
OR
AD204
+
+15V
–15V
250
4–20mA
1V
TO
5V
–15k
+
0V
TO
10V
10k
–
237
1k
AD589
6.8k
–15V
–1V TO
ADDITIONAL
CHANNELS
Figure 18. Process Current Input Isolator with Offset
The circuit as shown requires a source compliance of at least
5 V, but if necessary that can be reduced by using a lower value
of current-sampling resistor and configuring the input amplifier
for a small gain.
(NOTE: Circuit figures shown on this page are for SIP-style packages. Refer to
Page 3 for proper DIP package pinout.)
AD204
+7.5V
–7.5V CLK RET
CLK
–
+
VO = VI 1 +
50k
RG
0.15F
470k
470k
0.038F
49.9k
RG
AD OP-07
1F+
1F+
1F
+
39k
220M
HI
LO
OPTIONAL
OPEN INPUT
DETECTION
()
Figure 17. Input Amplifier and Filter for Sensor Signals
REV. D
AD202/AD204
–10–
High Compliance Current Source. In Figure 19, an isolator
is used to sense the voltage across current-sensing resistor R
S
to
allow direct feedback control of a high voltage transistor or FET
used as a high compliance current source. Since the isolator has
virtually no response to dc common-mode voltage, the closed-
loop current source has a static output resistance greater than
10
14
W even for output currents of several mA. The output
current capability of the circuit is limited only by power dissipa-
tion in the source transistor.
AD202
OR
AD204
100k
+15V
–15V
470pF
10k
+5V REF
+
–
VC
20k
LOAD
IL = VC
RS
–10V TO +250V
RS
1k
MPS
U10
1k
Figure 19. High Compliance Current Source
Motor Control Isolator. The AD202 and AD204 perform
very well in applications where rejection of fast common-mode
steps is important but bandwidth must not be compromised.
Current sensing in a fill-wave bridge motor driver (Figure 20) is
one example of this class of application. For 200 V common-mode
steps (1 ms rise time) and a gain of 50 as shown, the typical
response at the isolator output will be spikes of ±5 mV ampli-
tude, decaying to zero in less than 100 ms. Spike height can be
reduced by a factor of four with output filtering just beyond the
isolator’s bandwidth.
AD204
+
–
5V
M
5m20A
+
200V dc
–
100mV
Figure 20. Motor Control Current Sensing
Floating Current Source/Ohmmeter. When a small floating
current is needed with a compliance range of up to ±1000 V dc,
the AD204 can be used to both create and regulate the current.
This can save considerable power, since the controlled current
does not have to return to ground. In Figure 21, an AD589
reference is used to force a small fixed voltage across R. That
sets the current that the input op amp will have to return
through the load to zero its input. Note that the isolator’s out-
put isn’t needed at all in this application; the whole job is done
by the input section. However, the signal at the output could be
useful as it’s the voltage across the load, referenced to ground.
Since the load current is known, the output voltage is propor-
tional to load resistance.
AD204
LOAD
R
7.5V
1F
+
30k
AD589
+
–
V
O
= R
L
V
R
R
I
LOAD
= (2mA MAX)
V
LOAD
4V
1.23V
R
Figure 21. Floating Current Source
Photodiode Amplifier. Figure 22 shows a transresistance
connection used to isolate and amplify the output of a photo-
diode. The photodiode operates at zero bias, and its output
current is scaled by R
F
to give a 5 V full-scale output.
AD202
OR
AD204
0V TO 5V
500k
PHOTO
DIODE
10A
FS
Figure 22. Photodiode Amplifier
(NOTE: Circuit figures shown on this page are for SIP-style packages. Refer to
Page 3 for proper DIP package pinout.)
REV. D
AD202/AD204
–11–
OUTLINE DIMENSIONS
Dimensions shown in inches and (millimeters)
AD202/AD204 SIP Package
0.625
(15.9)
MAX
0.15 (3.81) TYP
135
26
31 33 37
38
32
4
0.05 (1.3)TYP
1.30 (33.0)
0.010 ⴛ 0.020
(0.25 ⴛ 0.51)
0.20 (5.1)
0.143
(3.63)
0.12
(3.05)
0.10 (2.5)
TYP
0.250 (6.3) TYP
0.260 (6.6) MAX
2.08 (52.8) MAX
FRONT VIEW
BOTTOM VIEW
C
L
AD202/AD204 SIDE
VIEW
NOTE: PIN 31 IS PRESENT ONLY ON AD202
PIN 33 IS PRESENT ONLY ON AD204
CONTROLLING DIMENSIONS ARE IN INCHES; MILLIMETER DIMENSIONS
(IN PARENTHESES) ARE ROUNDED-OFF MILLIMETER EQUIVALENTS FOR
REFERENCE ONLY AND ARE NOT APPROPRIATE FOR USE IN DESIGN
AC1058 Mating Socket
0.30 (7.62)
MAX
0.24
(6.10)
0.10 (2.5) DIA
BOTH ENDS
2.65 (7.30)
2.50 (63.50)
0.10 (2.50) TYP 0.075 (1.90) TYP
AC1058 CAN BE USED AS A SOCKET
FOR AD202,AD204 AND AD246
NOTE: AMP ZP SOCKET (PIN 2 – 382006 – 3)
MAY BE USED IN PLACE OF THE AC1058
CONTROLLING DIMENSIONS ARE IN INCHES; MILLIMETER DIMENSIONS
(IN PARENTHESES) ARE ROUNDED-OFF MILLIMETER EQUIVALENTS FOR
REFERENCE ONLY AND ARE NOT APPROPRIATE FOR USE IN DESIGN
AD246JY Package
0.330 (8.4) MAX
0.10 (2.5) NOM
0.625
(15.9)
MAX
0.115 (2.9)
SIDE
VIEW
0.015 (0.38)
0.010 (0.25)
1
2
13
12
0.10
(2.5)
0.115
(2.9)
C
L
BOTTOM
VIEW
0.05 (1.30)
NOM
0.10
(2.5)
MIN
0.995 (25.3) MAX
AD246JY
FRONT VIEW
0.55 (14.0)
0.197 (5.0) 0.015 (0.38)
0.010 (0.25)
CONTROLLING DIMENSIONS ARE IN INCHES; MILLIMETER DIMENSIONS
(IN PARENTHESES) ARE ROUNDED-OFF MILLIMETER EQUIVALENTS FOR
REFERENCE ONLY AND ARE NOT APPROPRIATE FOR USE IN DESIGN
AD202/AD204 DIP Package
1.60 (40.6)
BOTTOM
VIEW
38 37 36
123
22 21 20
18 19
0.700
(17.8)
MAX
0.015 (0.38)
0.350
(8.9)
MAX
0.018 (0.46)
SQUARE
0.10
(2.5)
MIN
2.100 (53.3) MAX
NOTE: PIN 20 IS PRESENT ONLY ON AD202
PIN 21 IS PRESENT ONLY ON AD204
CONTROLLING DIMENSIONS ARE IN INCHES; MILLIMETER DIMENSIONS
(IN PARENTHESES) ARE ROUNDED-OFF MILLIMETER EQUIVALENTS FOR
REFERENCE ONLY AND ARE NOT APPROPRIATE FOR USE IN DESIGN
AC1060 Mating Socket
2.35 (59.7)
2.60 (66.0)
0.50
(12.7)
0.10 (2.5) DIA
BOTH ENDS
0.70
(17.8)
0.125 (3.1)
TYP
0.30 (7.62)
MAX
CONTROLLING DIMENSIONS ARE IN INCHES; MILLIMETER DIMENSIONS
(IN PARENTHESES) ARE ROUNDED-OFF MILLIMETER EQUIVALENTS FOR
REFERENCE ONLY AND ARE NOT APPROPRIATE FOR USE IN DESIGN
AD246JN Package
FRONT VIEW
AD246JN
1.445 (36.7) MAX
0.100 (2.5)
MIN
0.35 (8.9)
MAX
0.020 (0.51)
0.010 (0.25)
0.145 (3.7)
0.020 (0.51)
0.015 (0.38)
112
1424
BOTTOM VIEW
1.10 (27.9)
1.00 (25.4)
0. 50
(12.7)
0.70
(17.8)
CONTROLLING DIMENSIONS ARE IN INCHES; MILLIMETER DIMENSIONS
(IN PARENTHESES) ARE ROUNDED-OFF MILLIMETER EQUIVALENTS FOR
REFERENCE ONLY AND ARE NOT APPROPRIATE FOR USE IN DESIGN
REV. D
–12–
C00483–0–10/02(D)
PRINTED IN U.S.A.
AD202/AD204
Revision History
Location Page
10/02—Data Sheet changed from REV. C to REV. D.
Deleted FUNCTIONAL BLOCK DIAGRAM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
Text added to GENERAL DESCRIPTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
Edits to SPECIFICATIONS TABLE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
Edits to Figure 4 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Edits to Input Configurations section . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Edit to High Compliance Current Source section . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Updated OUTLINE DIMENSIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
4/01—Data Sheet changed from REV. B to REV. C.
Change to SIP Package . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
