LTC1968 Linear Integrated Systems, LTC1968 Datasheet - Page 25

• Manufacturer Part Number: LTC1968
• Description: RMS-to-DC Converter
• Manufacturer: Linear Integrated Systems

APPLICATIO S I FOR ATIO
7. Output is noisy with >200kHz inputs.
8. Large errors occur at crest factors approaching, but
9. Screwy results, errors > spec limits, typically 1% to 5%.
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– This is a fundamental characteristic of this topol-
less than 4.
– Insufficient averaging.
– High impedance (12.5kΩ) and high accuracy (0.1%)
ogy. The LTC1968 is designed to work very well
with inputs of 100kHz or less. It works okay as high
as 1MHz, but it is limited by aliased ∆Σ noise.
Solution: Bandwidth limit the input or digitally filter
the resulting output.
Solution: Increase C
DC Waveforms” section for discussion of output
droop.
require clean boards! Flux residue, finger grime, etc.
all wreak havoc at this level.
Solution: Wash the board.
U
KEEP BOARD CLEAN
LTC1968
AVE
U
. See “Crest Factor and AC +
W
1968 TS09
U
10. Gain is low by ≅1% or more, no other problems.
– Probably due to circuit loading. With a DMM or a
– Loading can also be caused by cheap averaging
10× scope probe, Z
output is 12.5kΩ, resulting in – 0.125% gain
error. Output impedance is higher with the DC
accurate post filter.
Solution: Remove the shunt loading or buffer the
output.
capacitors.
Solution: Use a high quality metal film capacitor
for C
AVE
V
OUT
.
OUT RTN
LTC1968
LOADING DRAGS DOWN GAIN
12.5k
5
6
IN
200mV
= 10MΩ. The LTC1968
–0.125%
10M
RMS
DMM
IN
1968 TS10
DCV
mV
LTC1968
25
1968f