AD5429 datasheet(17/28 Pages) AD

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Data Sheet

AD5429/AD5439/AD5449

Rev. F | Page 17 of 28

SINGLE-SUPPLY APPLICATIONS

Voltage-Switching Mode

Figure 40 shows the DACs operating in voltage-switching mode.

The reference voltage, VIN, is applied to the IOUT1A pin; IOUT2A

is connected to AGND; and the output voltage is available at the

VREFA terminal. In this configuration, a positive reference voltage

results in a positive output voltage, making single-supply operation

possible. The output from the DAC is voltage at a constant

impedance (the DAC ladder resistance). Therefore, an op amp

is necessary to buffer the output voltage. The reference input

no longer sees a constant input impedance; instead, it sees one

that varies with code. Therefore, the voltage input should be

driven from a low impedance source.

Note that VIN is limited to low voltages because the switches

in the DAC ladder no longer have the same source-drain drive

voltage. As a result, their on resistance differs and degrades the

integral linearity of the DAC. Also, VIN must not go negative by

more than 0.3 V, or an internal diode turns on, causing the device

to exceed the maximum ratings. In this type of application, the

full range of multiplying capability of the DAC is lost.

VOUT

VDD

GND

VIN

IOUT2A

IOUT1A

RFBA VDD

VREFA

NOTES

1. ADDITIONAL PINS OMITTED FOR CLARITY.

2. C1 PHASE COMPENSATION (1pF TO 2pF) MAY BE REQUIRED

IF A1 IS A HIGH SPEED AMPLIFIER.

8-/10-/12-BIT

DAC

Figure 40. Single-Supply Voltage-Switching Mode

AD5429 Datasheet(PDF) 17 Page - Analog Devices