Test Circuits
(Continued)
TL H 5687 – 10
TL H 5687 – 9
FIGURE 7 Positive V
REF
(Note 7)
FIGURE 6 Reference Current Slew Rate Measurement (Note 7)
TL H 5687 – 11
FIGURE 8 Negative V
REF
(Note 7)
TL H 5687 – 12
Application Hints
REFERENCE AMPLIFIER DRIVE AND COMPENSATION
The reference amplifier provides a voltage at pin 14 for con-
verting the reference voltage to a current and a turn-around
circuit or current mirror for feeding the ladder The reference
amplifier input currrent I
14
must always flow 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
14
For bipolar reference signals as in the multiplying mode
FIGURE 9 Programmable Gain Amplifier or
Digital Attenuator Circuit (Note 7)
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 kX minimum capacitor values are 15
37 and 75 pF The capacitor may be tied to either V
EE
or
ground but using V
EE
increases negative supply rejection
7
NSC [ NATIONAL SEMICONDUCTOR ]
