DAC8420FSZ2 datasheet(18/24 Pages) AD

18 / 24 page

DAC8420

Rev. B | Page 18 of 24

is 16 mV. Thus, the best single-supply operation is obtained with

the output load connected to ground, so the output stage does not

have to sink current.

Like all amplifiers, the DAC8420 output buffers do generate

voltage noise, 52 nV/√Hz typically. This is easily reduced by

adding a simple RC low-pass filter on each output.

REFERENCE CONFIGURATION

The two reference inputs of the DAC8420 allow a great deal

of flexibility in circuit design. The user must take care, however,

to observe the minimum voltage input levels on VREFHI and

VREFLO to maintain the accuracy shown in the data sheet.

These input voltages can be set anywhere across a wide range

within the supplies, but must be a minimum of 2.5 V apart in

any case (see Figure 30). A wide output voltage range can be

obtained with ±5 V references, which can be provided by the

AD588 as shown in Figure 33. Many applications utilize the

DACs to synthesize symmetric bipolar waveforms, which

require an accurate, low drift bipolar reference. The AD588

provides both voltages and needs no external components.

Additionally, the part is trimmed in production for 12-bit

accuracy over the full temperature range without user calibra-

tion. Performing a clear with the reset select CLSEL high allows

the user to easily reset the DAC outputs to midscale, or 0 V in

these applications.

When driving the reference inputs VREFHI and VREFLO, it is

important to note that VREFHI both sinks and sources current,

and that the input currents of both are code dependent. Many

voltage reference products have a limited current sinking

capability and must be buffered with an amplifier to drive

VREFHI in order to maintain overall system accuracy. The

input VREFLO, however, has no such requirement.

DAC8420

0.1µF

+15V

SUPPLY

–15V

SUPPLY

SYSTEM

GROUND

+5V

–5V

+VS

–VS

AD588

1µF

DAC A

DAC B

DAC C

DAC D

DIGITAL

CONTROLS

GND

DIGITAL INPUTS

VREFHI

+5V

VREFLO

–5V

+15V SUPPLY

0.1µF

–15V SUPPLY

0.1µF

VOUTA

VOUTB

VOUTC

VOUTD

Figure 33. ±10 V Bipolar Reference Configuration Using the AD588

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