AD5252 datasheet(24/28 Pages) AD

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AD5251/AD5252

Rev. 0 | Page 24 of 28

RSENSE

0.1k

Ω

RDAC1

10k

Ω

RDAC3

10k

Ω

AD5252

AD8628

VREF

+5V

V+

V–

APPLICATIONS

LCD PANEL VCOM ADJUSTMENT

Large LCD panels usually require an adjustable VCOM voltage

centered around 6 V to 8 V with ±1 V swing and small steps

adjustment. This example represents common DAC appli-

cations where the window of adjustments is small and centered

at any level. High voltage and high resolution DACs can be used

but it is far more cost-effective to use low voltage digital

potentiometers with level shifting, such as the AD5251 or

AD5252, to achieve the objective.

Assume a VCOM voltage requirement of 6 V ±1 V with a ±20 mV

step adjustment, as shown in Figure 44. The AD5252 can be

configured in voltage divider mode with an op amp gain. With

±20% tolerance accounted for by the AD5252, this circuit can

still be adjusted from 5 V to 7 V with an 8 mV/step in the

worst case.

Figure 45. Current-Sensing Amplifier.

ADJUSTABLE HIGH POWER LED DRIVER

Figure 46 shows a circuit that can drive three to four high power

LEDs. The ADP1610 is an adjustable boost regulator that

provides adequate headroom and current for the LEDs. Because

its FB pin voltage is 1.2 V, the digital potentiometer AD5252

and the op amp form an average gain of 12 feedback networks

that servo the sensing and feedback voltages. As a result, the

voltage across RSET is regulated around 0.1 V, depending on the

AD5252’s setting. An adjustable LED current is

VDD

VCOM

+5V

10k

18.5k

350k

2.2p

AD5252

+14.4V

±20%

±1%

± 1V

V+

V–

SET

LED

SET

(9)

RSET should be small to conserve power but large enough to

limit the maximum LED current. R3 should also be used in

parallel with the AD5252 to limit the LED current within an

achievable range.

Figure 44. Apply 5 V Digital Potentiometer AD5251 in a 6 V ±1 V Application.

/SD

COMP

GND

PWM

390pF

CSS

10nF

100k

Ω

RSET

0.25k

Ω

10k

Ω

0.1

µF

AD5252

ADP1610

VOUT

AD8591

+5V

V+

V–

200

Ω

1.1k

Ω

100

Ω

13.5k

Ω

µF

CURRENT-SENSING AMPLIFIER

The dual channel, synchronous update, and channel-to-channel

resistance matching characteristics make the AD5251/AD5252

suitable for current sensing applications, such as LED

brightness control. In the circuit shown in Figure 45, when

RDAC1 and RDAC3 are programmed to the same settings, it

can be shown that

()

REF

−

(8)

As a result, the current through a sense resistor connected

between V1 and V2 can be known. The programmability of this

circuit makes it adaptable to systems that require different sen-

sitivities. If the op amp has very low offset and low bias current,

the major source of error comes from the digital potentiometer

channel-to-channel resistance mismatch, which is typically

0.15%. The circuit accuracy is about 9 bits, which is adequate

for LED control and other general purpose applications.

Figure 46. High Power Adjustable LED Driver

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