AD202(1994) Просмотр технического описания (PDF) - Analog Devices
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AD202 Datasheet PDF : 12 Pages
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AD202/AD204
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) which 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 stand-alone op-
eration 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.
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.
FB
4
IN–
3
IN+
1
VSIG
2
IN COM
+VISO OUT 6
–VISO OUT 5
+7.5V
–7.5V
SIGNAL
MOD
±5V
FS
AD202
DEMOD
HI
38
±5V
F.S.
VOUT
LO
37
RECT &
FILTER
POWER
25kHz
OSCILLATOR
25kHz
31 +15V DC
32 POWER
RETURN
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 ca-
pacitor is provided in the module.
Figure 1a. AD202 Functional Block Diagram
FB
4
IN–
3
IN+
1
VSIG
2
IN COM
+VISO OUT 6
–VISO OUT 5
+7.5V
–7.5V
AD204
SIGNAL DEMOD
MOD
±5V
FS
HI
38
±5V
VOUT
F.S. LO
37
RECT &
FILTER
POWER
25kHz
25kHz
POWER
CONV.
CLOCK
33 (15V
p-p/25kHz)
32 POWER
RETURN
Figure 3a.
Powering the AD204. The AD204 gets its power from an ex-
ternally supplied clock signal (a 15 V p-p square wave with a
nominal frequency of 25 kHz) as shown in Figure 3b.
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 which 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 which is generated internally in the case of the AD202, or
supplied externally for the AD204.
Within the signal swing limits of approximately ± 5 V, the output
voltage of the isolator is equal to the output voltage of the op
amp; that is, the isolation barrier has unity gain. The output sig-
nal 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
Figure 3b.
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
(Circuit figures shown on this page are for SIP style pack-
ages. Refer to page 3 for proper DIP package pinout.)
–4–
REV. B
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