Download Comparator - TI E2E Community

Op Amp Performance
In Comparator Applications
Neil P. Albaugh
May, 2000
Characteristics: op amp comparator
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•
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Closed loop stability
logic output
inverting & non-inv
speed
precision
wide differential input voltage
range
• open collector out
Yes
no *
yes
no
yes
yes *
no
no
yes
yes
yes
no
yes
yes *
* check !
2
OPA350 Response Time
5v
t hr eshol d 2.5v
vh
Vl
0v
50 mil l ivol t s over dr ive
OPA340 Response Time
5v
t hr eshol d 2.5v
vh
Vl
0v
50 mil l ivol t s over dr ive
OPA345 Response Time
5v
t hr eshol d 2.5v
vh
Vl
0v
50 mil l ivol t s over dr ive
OPA347 Response Time
5v
t hr eshol d 2.5v
vh
Vl
0v
50 mil l ivol t s over dr ive
OPA338 Response Time
5v
t hr eshol d 2.5v
vh
Vl
0v
50 mil l ivol t s over dr ive
OPA336 Response Time
5v
t hr eshol d 2.5v
vh
Vl
0v
50 mil l ivol t s over dr ive
OPA130 Response Time
5v
t hr eshol d 2.5v
vh
Vl
0v
50 mil l ivol t s over dr ive
OPA131 Response Time
5v
t hr eshol d 2.5v
????
vh
Vl
0v
50 mil l ivol t s over dr ive
OPA132 Response Time
5v
t hr eshol d 2.5v
vh
Vl
0v
50 mil l ivol t s over dr ive
OPA132 Response Time +/-15V
+15v
t hr eshol d 2.5v
vh
Vl
0v
-15v
50 mil l ivol t s over dr ive
Sometimes slower is better
• Lower output slew rate means
less radiated emi & rfi
• smaller power supply current glitch
opa350 output f f t spectr um
1 MHz squar e wave input
l m111 out put f f t spect r um
1 MHz squar e wave input
Bad op amps for comparators
• Diode- clamped
differential input
types
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•
•
•
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Opa227 & opa228
opa277
opa177 & opa77
opa27 & opa37
others ???
Caution
can input voltage exist when supplies are off ?
If so, add resistors in series with inputs to limit
current to about
10 milliamps or less
inst r ument at ion ampl if ier + compar at or
Vthreshold
over / under t emper at ur e al ar m
compr essor on / of f cont r ol
"g" l oad al ar m
over st r ess al ar m