LTC1966 Linear Technology, LTC1966 Datasheet - Page 27

• Manufacturer Part Number: LTC1966
• Description: SIGMA RMS-to-DC Converter
• Manufacturer: Linear Technology

APPLICATIO S I FOR ATIO
TROUBLESHOOTING GUIDE
Top Ten LTC1966 Application Mistakes
1. Circuit won’t work–Dead On Arrival–no power drawn.
2. Circuit won’t work, but draws power. Zero or very
3. Screwy results, particularly with respect to linearity
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or high crest factors; differential input application.
– Probably AC-coupled both input pins.
– Probably forgot to enable the LTC1966 by pulling
little output, single-ended input application.
– Probably didn’t connect both input pins.
Pin 8 low.
Solution: Tie Pin 8 to Pin 1.
Solution: Tie both inputs to something. See “Input
Connections” in the Design Cookbook.
Solution: Make at least one input DC-coupled. See
“Input Connections” in the Design Cookbook.
DC-COUPLE ONE INPUT
2
3
IN1
IN2
LTC1966
U
CONNECT PIN 3
NC
U
2
3
IN1
IN2
LTC1966
1966 TS02
W
DC-CONNECT ONE INPUT
2
3
IN1
IN2
LTC1966
U
1966 TS03
4. Gain is low by a few percent, along with other screwy
5. Offsets perceived to be out of specification because 0V
6. Linearity perceived to be out of specification particu-
results.
– Probably tried to use output in a floating, differential
in 0V out.
– The offsets are not specified at 0V in. No RMS-to-
larly with small input signals.
– This could again be due to using 0V in as one of the
– The input offset voltage can cause small AC linear
manner.
Solution: Tie Pin 6 to a low impedance. See “Output
Connections” in the Design Cookbook.
DC converter works well at 0 due to a divide-by-zero
calculation.
Solution: Measure V
ings > 5mV
measurement points.
Solution: Check Linearity from 5mV
500mV
ityerrors at low input amplitudes as well. See “Error
Analyses” section.
Possible Solution: Include a trim for input offset.
RMS
.
OUT RTN
LTC1966
DC
V
OUT
.
GROUND PIN 6
5
6
IOS
/V
31
30
OOS
HI
LO
TYPE 7136
ADC
by extrapolating read-
1966 TS04
LTC1966
sn1966 1966fas
RMS
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