Datasheet AD202, AD204 (Analog Devices) - 5

AD202/AD204 AD246 Clock Driver.
The AD246 is a compact, inexpensive
AD202
clock driver that can be used to obtain the required clock from a
OR
single 15 V supply. Alternatively, the circuit shown in Figure 4
RF AD204 100pF
(essentially an AD246) can be used. In either case, one clock
VO 2k
circuit can operate at least 32 AD204s at the rated minimum
R
supply voltage of 14.25 V and one additional isolator can be
V F
( )
V O = V SIG 1 + ––– R SIG R G G
operated for each 40 mV increase in supply voltage up to 15 V.
RF 20k
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 Figure 6. Input Connections for Gain > 1 five isolators used. Place the capacitor as close as possible to the clock driver. The noninverting circuit of Figures 5 and 6 can also be used to your advantage when a signal inversion is needed: just interchange
15V
either the input leads or the output leads to get inversion. This
14 6 5 6
approach retains the high input resistance of the noninverting
180pF TELEDYNE 1N914 1
circuit, and at unity gain no gain-setting resistors are needed.
C TSC426 3 10 2 7 CLK RC Q CD OUT
When the isolator is not powered, a negative input voltage of
2 R 4047B 4 5 +
more than about 2 V will cause an input current to flow. If the
49.9k 1 F 35V
signal source can supply more than a few mA under such con-
1N914 12 9 8 7 4 3
ditions, the 2 kW resistor shown in series with IN+ should be
CLK AND PWR COM
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 Figure 4. Clock Driver is present.
Input Configurations.
The AD202 and AD204 have been Figure 7 shows how to accommodate current inputs or sum designed to be very easy to use in a wide range of applications. currents or voltages. This circuit can also be used when the The basic connection for standard unity gain applications, useful input signal is larger than the ± 5 V input range of the isolator; for signals up to ± 5 V, is shown in Figure 5; some of the possible for example, a ± 50 V input span can be accommodated with variations are described below. When smaller signals must be RF = 20 kW and RS = 200 kW. Once again, a capacitor from FB handled, Figure 6 shows how to achieve gain while preserving a to IN COM is required for gains above five. very high input resistance. The value of feedback resistor RF should be kept above 20 kW for best results. Whenever a gain of
IS
more than five is taken, a 100 pF capacitor from FB to IN COM
AD202 OR
is required. At lower gains this capacitor is unnecessary, but it
RF AD204 RS2
will not adversely affect performance if used.
V RS1 VS2 FB VS1 IN– OUT 2k HI (SEE TEXT) IN+ VSIG VOUT OUT ( 5V) 5V IN COM LO R R V = –
(
V F F S1 ––– + V S2 ––– + IS RF + ...
)
RS1 RS2 15V OR RF 20k AD202 CLOCK OR
Figure 7. Connections for Summing or Current Inputs
AD204
Figure 5. Basic Unity-Gain Application (NOTE: Circuit figures shown on this page are for SIP-style packages. Refer to Page 3 for proper DIP package pinout.) REV. D –5– 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