+

+

Analog

Power

Supply

Load

15V

2R

5V

R

15V

A1

R

R

R

2R

2R

2R

R

5 kW

S2

S1

DGND

DGND

V

X

REF

V

DD

R X

FB

I

X

OUT

V

OUT

V

CC

V

EE

A

X

GND

Digitalinterfaceconnectionsomittedforclarity.

SwitchesS1andS2areclosed,V

mustbepowered.

DD

OUT

REF

D

V

V

65 536

=

´

DAC8812

SBAS349C – AUGUST 2005 – REVISED NOVEMBER 2015

www.ti.com

Feature Description (continued)

used by the logic to drive the DAC switches on and off. Note that a matching switch is used in series with the

internal 5 k

according to Equation 1:

(1)

The DAC is also designed to accommodate ac reference input signals. The DAC8812 accommodates input

reference voltages in the range of –15 V to 15 V. The reference voltage inputs exhibit a constant nominal input

resistance of 5 k

various output resistances and capacitances.

The choice of external amplifier should take into account the variation in impedance generated by the DAC8812

on the amplifiers' inverting input node. The feedback resistance, in parallel with the DAC ladder resistance,

dominates output voltage noise. For multiplying mode applications, an external feedback compensation

changes in reference input voltages.

Figure 15 shows the gain vs frequency performance at various attenuation settings using a 3 pF external

power-supply bypassing of 0.01

μF, in parallel with 1 μF, is recommended. Under these conditions, clean power

supply with low ripple voltage capability should be used. Switching power supplies is usually not suitable for this

DAC8812 5-V supply from the system analog supply voltages (do not use the digital 5-V supply); see Figure 31.

Figure 31. Recommended Kelvin-Sensed Hookup

14

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