AD628

Rev. C | Page 17 of 20

CURRENT LOOP RECEIVER

Analog data transmitted on a 4 to 20 mA current loop may be

detected with the receiver shown in Figure 33. The AD628 is an

ideal choice for such a function, because the current loop must

be 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 may be used to monitor a

battery charger. Voltages approximately eight times the power

supply voltage may 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.

+IN

–IN

G = +0.1

10k

Ω

10k

Ω

AD628

+IN

–IN

A2

OUT

–IN

250

Ω

250

Ω

100k

Ω

A1

+15V

+IN

100k

Ω

–15V

10k

Ω

11k

Ω

100k

Ω

2.5V

REF

0V TO 5V

TO ADC

4–20mA

SOURCE

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

+IN

–IN

G = +0.1

10k

Ω

A1

–IN

100k

Ω

5V

+IN

–IN

A2

OUT

AD628

100k

Ω

10k

Ω

OTHER

BATTERIES IN

CHARGING

CIRCUIT

CHARGING

CIRCUIT

+1.5V

BATTERY

10k

Ω

+IN

10k

Ω

0V TO 5V

TO ADC

Figure 34. Battery Voltage Monitor