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 Table 1, as well as Equation 2.

6

8

1

4

5

7

2

3

AD628

+15V

+2.5V

9.53kΩ

–15V

10kΩ

0V TO 5V

TO ADC

I = 4 TO 20mA

100kΩ

210kΩ

100kΩ

100kΩ

249Ω

10kΩ

10kΩ

249Ω

Figure 33. Level Shifter for 4 to 20 mA Current Loop

+IN

–IN

G= +0.1

10kΩ

A1

–IN

100kΩ

–5V

–IN

A2

OUT

AD628

100kΩ

10kΩ

CHARGING

CIRCUIT

+1.5V

BATTERY

10kΩ

+IN

10kΩ

TO ADC

OTHER

BATTERIES IN

CHARGING

CIRCUIT

+5V

+IN

Figure 34. Battery Voltage Monitor