Datasheet

AD628
Rev. G | Page 18 of 20
CURRENT LOOP RECEIVER
Analog data transmitted on a 4 to 20 mA current loop can be
detected with the receiver shown in
Figure 33. The AD628 is an
ideal choice for such a function because the current loop is
driven with a compliance voltage sufficient to stabilize the loop,
and the resultant common-mode voltage often exceeds commonly
used supply voltages. Note that with large shunt values, a resistance
of equal value must be inserted in series with the inverting
input to compensate for an error at the noninverting input.
MONITORING BATTERY VOLTAGES
Figure 34 illustrates how the AD628 is used to monitor a battery
charger. Voltages approximately eight times the power supply
voltage can be applied to the input with no damage. The resistor
divider action is well suited for the measurement of many
power supply applications, such as those found in battery
chargers or similar equipment.
For proper operation, the common-mode voltage must satisfy
the input specifications in
Tabl e 1, as well as Equation 2.
6
8
1
4
5
7 23
AD628
+15V
+2.5V 9.53k
–15V
10k
0V TO 5V
TO ADC
I = 4 TO 20mA
100k
210k 100k
100k249
V
CM
= 15V
10k
10k
2
49

02992-031
Figure 33. Level Shifter for 4 to 20 mA Current Loop
+IN
–IN
G=+0.1
10k
A1
–IN
100k
V
REF
–5V
–IN
A2
OUT
AD628
100k
10k
CHARGING
CIRCUIT
+1.5V
BATTERY
10k
+IN
nV
BAT
(V)
R
EXT1
10k
TO ADC
C
FILT
R
G
02992-032
OTHER
BATTERIES IN
CHARGING
CIRCUIT
+5V
+IN
Figure 34. Battery Voltage Monitor