dac0808lcmx National Semiconductor Corporation, dac0808lcmx Datasheet - Page 9

• Manufacturer Part Number: dac0808lcmx
• Description: 8-bit D/a Converter
• Manufacturer: National Semiconductor Corporation

Test Circuits
Application Hints
REFERENCE AMPLIFIER DRIVE AND COMPENSATION
The reference amplifier provides a voltage at pin 14 for
converting the reference voltage to a current, and a
turn-around circuit or current mirror for feeding the ladder.
The reference amplifier input currrent, I
into pin 14, regardless of the set-up method or reference
voltage polarity.
Connections for a positive voltage are shown in Figure 7 .
The reference voltage source supplies the full current I
(Continued)
14
FIGURE 9. Programmable Gain Amplifier or
, must always flow
FIGURE 8. Negative V
Digital Attenuator Circuit (Note 8)
14
.
9
For bipolar reference signals, as in the multiplying mode,
R15 can be tied to a negative voltage corresponding to the
minimum input level. It is possible to eliminate R15 with only
a small sacrifice in accuracy and temperature drift.
The compensation capacitor value must be increased with
increases in R14 to maintain proper phase margin; for R14
values of 1, 2.5 and 5 k , minimum capacitor values are 15,
37 and 75 pF. The capacitor may be tied to either V
ground, but using V
A negative reference voltage may be used if R14 is
grounded and the reference voltage is applied to R15 as
shown in Figure 8 . A high input impedance is the main
REF
(Note 8)
DS005687-11
DS005687-12
EE
increases negative supply rejection.
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