Datasheet AD202, AD204 (Analog Devices) - 4

AD202/AD204 DIFFERENCES BETWEEN THE AD202 AND AD204
the output leads to get signal inversion. Additionally, in multi- The primary distinction between the AD202 and AD204 is in channel applications, the unbuffered outputs can be multiplexed the method by which they are powered: the AD202 operates with one buffer following the mux. This technique minimizes directly from 15 V dc while the AD204 is powered by a non- offset errors while reducing power consumption and cost. The isolated externally-supplied clock (AD246) that can drive up to output resistance of the isolator is typically 3 kΩ for the AD204 32 AD204s. The main advantages of using the externally- (7 kΩ for AD202) and varies with signal level and temperature, clocked AD204 over the AD202 are reduced cost in multichannel so it should not be loaded (see Figure 2 for the effects of load applications, lower power consumption, and higher bandwidth. upon nonlinearity and gain drift). In many cases, a high imped- In addition, the AD204 can supply substantially more isolated ance load will be present or a following circuit such as an output power than the AD202. filter can serve as a buffer so that a separate buffer function will Of course, in a great many situations, especially where only one not often be needed. or a few isolators are used, the convenience of standalone opera-
NON- GAIN GAIN TC
tion provided by the AD202 will be more significant than any
LINEARITY CHANGE CHANGE (%) (%) (ppm/
ⴗ
C)
of the AD204’s advantages. There may also be cases where it is
0.25 –10 –500
desirable to accommodate either device interchangeably, so the pinouts of the two products have been designed to make that easy to do.
0.20 –8 –400 FB AD202 0.15 –6 AD202 GAIN AND GAIN TC –300 IN– SIGNAL DEMOD AD202 NONLINEARITY HI MOD IN+
ⴞ
–4 –200 5V
ⴞ
5V V 0.10 AD204 GAIN AND GAIN TC V OUT SIG FS FS LO IN COM +7.5V –2 POWER 0.05 –100 +VISO OUT RECT AND OSCILLATOR 15V DC –7.5V –V FILTER ISO OUT 25kHz 25kHz AD204 NONLINEARITY POWER 0 0 0 RETURN 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 OUTPUT LOAD – M
⍀ Figure 1a. AD202 Functional Block Diagram Figure 2. Effects of Output Loading
USING THE AD202 AND AD204 FB AD204 Powering the AD202.
The AD202 requires only a single 15 V
IN– SIGNAL DEMOD
power supply connected as shown in Figure 3a. A bypass capaci-
HI MOD IN+
tor is provided in the module. ⴞ
5V
ⴞ
5V V V OUT SIG FS FS LO AD202 IN COM +7.5V POWER +VISO OUT RECT CLOCK POWER 15V
ⴞ
5% AND 15V p-p –7.5V CONV. –V FILTER 25kHz ISO OUT 25kHz 25kHz POWER 15V RETURN RETURN
Figure 1b. AD204 Functional Block Diagram Figure 3a. (Pin Designations Apply to the DIP-Style Package)
Powering the AD204.
The AD204 gets its power from an
INSIDE THE AD202 AND AD204
externally supplied clock signal (a 15 V p-p square wave with a The AD202 and AD204 use an amplitude modulation technique nominal frequency of 25 kHz) as shown in Figure 3b. to permit transformer coupling of signals down to dc (Figure 1a and 1b). Both models also contain an uncommitted input op
AD246
amp and a power transformer that provides isolated power to
AD204 AD204 AD204 15V
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.
15V RETURN
Within the signal swing limits of approximately ± 5 V, the out- put voltage of the isolator is equal to the output voltage of the Figure 3b. op amp; that is, the isolation barrier has unity gain. The output signal is not internally buffered, so the user is free to interchange (NOTE: Circuit figures shown on this page are for SIP-style packages. Refer to Page 3 for proper DIP package pinout.) –4– REV. D Document Outline FEATURES APPLICATIONS GENERAL DESCRIPTION PRODUCT HIGHLIGHTS SPECIFICATIONS AD246–SPECIFICATIONS AD246 Pin Designations PIN DESIGNATIONS ORDERING GUIDE DIFFERENCES BETWEEN THE AD202 AND AD204 INSIDE THE AD202 AND AD204 USING THE AD202 AND AD204 Powering the AD204 AD246 Clock Drive Input Configurations Adjustments Common-Mode Performance Dynamics and Noise Using Isolated Power Operation at Reduced Signal Swing PCB Layout for Multichannel Applications Synchronization APPLICATIONS EXAMPLES Low Level Sensor Inputs Process Current Input with Offset High Compliance Current Source Motor Control Isolator. Floating Current Source/Ohmmeter Photodiode Amplifier OUTLINE DIMENSIONS Revision History