AD5231 datasheet(24/28 Pages) AD

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AD5231

Data Sheet

Rev. D | Page 24 of 28

V+

V–

AD8552

AD5231

V+

V–

AD8552

–2.5VREF

+2.5VREF

VOUT

VIN

TRIM

GND

ADR421

+5V

–5V

+5V

Figure 49. 10-Bit Bipolar DAC

10-BIT UNIPOLAR DAC

Figure 50 shows a unipolar 10-bit DAC using AD5231. The

buffer is needed to drive various leads.

AD5231

V+

V–

AD8601

GND

AD1582

VOUT

VIN

Figure 50. 10-Bit Unipolar DAC

PROGRAMMABLE VOLTAGE SOURCE WITH

BOOSTED OUTPUT

For applications that require high current adjustment, such as a

laser diode driver or tunable laser, a boosted voltage source can

be considered (see Figure 51).

AD5231

V+

V–

AD8601

VIN

VOUT

2N7002

RBIAS

SIGNAL CC

Figure 51. Programmable Booster Voltage Source

In this circuit, the inverting input of the op amp forces the VOUT

to be equal to the wiper voltage set by the digital potentiometer.

The load current is then delivered by the supply via the

N-Ch FET N1. N1 power handling must be adequate to dissipate

(Vi − VO) × IL power. This circuit can source a maximum of

100 mA with a 5 V supply.

For precision applications, a voltage reference such as ADR421,

ADR03, or ADR370 can be applied at Terminal A of the digital

potentiometer.

PROGRAMMABLE CURRENT SOURCE

A programmable current source can be implemented with the

circuit shown in Figure 52.

V+

V–

OP1177

VIN

SLEEP

REF191

GND

VOUT

AD5231

+5V

–5V

+5V

–2.048V TO VL

0V TO (2.048V + VL)

102Ω

1µF

100Ω

Figure 52. Programmable Current Source

REF191 is a unique low supply, headroom precision reference

that can deliver the 20 mA needed at 2.048 V. The load current

is simply the voltage across Terminals B–W of the digital

potentiometer divided by RS:

1024

REF

(7)

The circuit is simple, but be aware that there are two issues.

First, dual-supply op amps are ideal because the ground

potential of REF191 can swing from −2.048 V at zero scale to VL

at full scale of the potentiometer setting. Although the circuit

works under single-supply, the programmable resolution of the

system is reduced. Second, the voltage compliance at VL is

limited to 2.5 V or equivalently a 125 Ω load. Should higher

voltage compliance be needed, users can consider digital

potentiometers AD5260, AD5280, and AD7376. Figure 53

shows an alternate circuit for high voltage compliance.

To achieve higher current, such as when driving a high power

LED, the user can replace the UI with an LDO, reduce RS, and

add a resistor in series with the digital potentiometer’s

A terminal. This limits the potentiometer’s current and

increases the current adjustment resolution.

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