Datasheet

LF155, LF156, LF355, LF356, LF357
SNOSBH0C –MAY 2000–REVISED MARCH 2013 www.ti.com
Figure 55. Fast Sample and Hold
• Both amplifiers (A1, A2) have feedback loops individually closed with stable responses (overshoot negligible)
• Acquisition time T
A
, estimated by:
• LF156 develops full S
r
output capability for V
IN
≥ 1V
• Addition of SW2 improves accuracy by putting the voltage drop across SW1 inside the feedback loop
• Overall accuracy of system determined by the accuracy of both amplifiers, A1 and A2
Figure 56. High Accuracy Sample and Hold
• By closing the loop through A2, the V
OUT
accuracy will be determined uniquely by A1.
– No V
OS
adjust required for A2.
• T
A
can be estimated by same considerations as previously but, because of the added
– propagation delay in the feedback loop (A2) the overshoot is not negligible.
• Overall system slower than fast sample and hold
• R1, C
C
: additional compensation
• Use LF156 for
– Fast settling time
– Low V
OS
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