LTC1967_15 Datasheet, PDF (24/28 Pages) Linear Technology – Precision Extended Bandwidth, RMS-to-DC Converter

LTC1967
APPLICATIO S I FOR ATIO
TROUBLESHOOTING GUIDE
Top Ten LTC1967 Application Mistakes
1. Circuit won’t work–Dead On Arrival–no power drawn.
– Probably forgot to enable the LTC1967 by pulling
Pin␣ 8 low.
Solution: Tie Pin 8 to Pin 1.
2. Circuit won’t work, but draws power. Zero or very
little output, single-ended input application.
– Probably didn’t connect both input pins.
Solution: Tie both inputs to something. See “Input
Connections” in the Design Cookbook.
CONNECT PIN 3
4. Gain is low by a few percent, along with other screwy
results.
– Probably tried to use output in a floating, differential
manner.
Solution: Tie Pin 6 to a low impedance. See “Output
Connections” in the Design Cookbook.
GROUND PIN 6
LTC1967
5
V_OUT
6
OUT RTN
TYPE 7136
31 _HI ADC
30
LO
1967 TS04
2
IN1
LTC1967
3
NC IN2
1967TS02
3. Screwy results, particularly with respect to linearity
or high crest factors; differential input application.
– Probably AC-coupled both input pins.
Solution: Make at least one input DC-coupled. See
“Input Connections” in the Design Cookbook.
DC-COUPLE ONE INPUT
DC-CONNECT ONE INPUT
2
IN1
LTC1967
3
IN2
2
IN1
LTC1967
3
IN2
5. Offsets perceived to be out of specification because 0V
in ≠ 0V out.
– The offsets are not specified at 0V in. No RMS-to-
DC converter works well at 0 due to a divide-by-zero
calculation.
Solution: Measure V_IOS/V_OOS by extrapolating read-
ings > ±5mV_DC.
6. Linearity perceived to be out of specification particu-
larly with small input signals.
– This could again be due to using 0V in as one of the
measurement points.
Solution: Check Linearity from 5mV_RMS to
500mV_RMS.
– The input offset voltage can cause small AC linear
ityerrors at low input amplitudes as well. See “Error
Analyses” section.
Possible Solution: Include a trim for input offset.
1967 TS03
1967f
24