DAC0832LCWMXSLASHNOPB datasheet(16/29 Pages) TI

16 / 29 page

DAC0830, DAC0832

SNAS534B – MAY 1999 – REVISED MARCH 2013

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This configuration offers several useful application advantages. Since the output is a voltage, an external op amp

is not necessarily required but the output impedance of the DAC is fairly high (equal to the specified reference

input resistance of 10 k

Ω to 20 kΩ) so an op amp may be used for buffering purposes. Some of the advantages

of this mode are illustrated in Figure 23, Figure 24, Figure 25, and Figure 26.

There are two important things to keep in mind when using this DAC in the voltage switching mode. The applied

reference voltage must be positive since there are internal parasitic diodes from ground to the IOUT1 and IOUT2

terminals which would turn on if the applied reference went negative. There is also a dependence of conversion

linearity and gain error on the voltage difference between VCC and the voltage applied to the normal current

output terminals. This is a result of the voltage drive requirements of the ladder switches. To ensure that all 8

switches turn on sufficiently (so as not to add significant resistance to any leg of the ladder and thereby introduce

additional linearity and gain errors) it is recommended that the applied reference voltage be kept less than +5VDC

and VCC be at least 9V more positive than VREF. These restrictions ensure less than 0.1% linearity and gain error

change. Figure 27, Figure 28, and Figure 29 characterize the effects of bringing VREF and VCC closer together as

well as typical temperature performance of this voltage switching configuration.

•

Voltage switching mode eliminates output signal inversion and therefore a need for a negative power supply.

•

Zero code output voltage is limited by the low level output saturation voltage of the op amp. The 2 k

Ω pull-down

resistor helps to reduce this voltage.

•

VOS of the op amp has no effect on DAC linearity.

Figure 23. Single Supply DAC

Figure 24. Obtaining a Bipolar Output from a Fixed Reference with a Single Op Amp

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DAC0832LCWMX/NOPB Datasheet(PDF) 16 Page - Texas Instruments