AD5263BRUZ200-R7 datasheet(25/28 Pages) AD

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Data Sheet

AD5263

Rev. F | Page 25 of 28

PROGRAMMABLE 4 TO 20 MA CURRENT SOURCE

A programmable 4–20 mA current source can be implemented

with the circuit shown in Figure 63. The REF191 is a unique low

supply headroom and high current handling precision reference

that can deliver 20 mA at +2.048 V. The load current is simply

the voltage across Terminal B to Terminal W of the digital

potentiometer divided by RS:

REF

(7)

–2.048V TO VL

0 TO (2.048V + VL)

+5V

–5V

102Ω

100Ω

REF191

GND

VIN

VOUT

SLEEP

AD5263

1µF

OP8510

V+

V–

Figure 63. Programmable 4–20 mA Current Source

The circuit is simple, but beware of two things. First, dual-supply

op amps are ideal because the ground potential of the REF191

can swing from −2.048 V at zero scale to VL at full scale of the

potentiometer setting. Although the circuit works with a single

supply, the programmable resolution of the system is reduced.

For applications that demand higher current capabilities, a few

changes to the circuit in Figure 63 produce an adjustable current in

the range of hundreds of mA. First, the voltage reference needs

to be replaced with a high current, low dropout regulator, such

as the ADP3333, and the op amp needs to be swapped with a

high current, dual-supply model, such as the AD5263. Depending

on the desired range of current, an appropriate value for RS

must be calculated. Because of the high current flowing to the

load, the user must pay attention to the load impedance so as

not to drive the op amp past the positive rail.

PROGRAMMABLE BIDIRECTIONAL CURRENT

SOURCE

For applications that require bidirectional current control or

higher voltage compliance, a Howland current pump can be a

solution (see Figure 64). If the resistors are matched, the load

current is

R2B

R2A

)

(

(8)

AD5263

+5V

150kΩ

R2A

14.95kΩ

R2B

50Ω

15kΩ

10pF

150kΩ

500Ω

+15V

V+

OP2177

V–

V+

V–

–5V

–15V

Figure 64. Programmable Bidirectional Current Source

R2B, in theory, can be made as small as needed to achieve the

current needed within the A2 output current driving capability.

In this circuit, OP2177 can deliver ±5 mA in either direction,

and the voltage compliance approaches +15 V. It can be shown

that the output impedance is

)

(

)

(

R2B

R2A

′

−

′

(9)

This output impedance can be infinite if resistors R1′ and R2′

match precisely with R1 and R2A + R2B, respectively. On the

other hand, it can be negative if the resistors are not matched.

As a result, C1 in the range of 1 pF to 10 pF is needed to prevent

oscillation.

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