LTC1968 datasheet(24/28 Pages) LINER

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LTC1968

1968f

APPLICATIO S I FOR ATIO

TROUBLESHOOTING GUIDE

Top Ten LTC1968 Application Mistakes

1. Circuit won’t work–Dead On Arrival–no power drawn.

– Probably forgot to enable the LTC1968 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.

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.

LTC1968

CONNECT PIN 3

IN1

IN2

1968TS02

LTC1968

IN1

IN2

1968 TS03

DC-COUPLE ONE INPUT

LTC1968

DC-CONNECT ONE INPUT

IN1

IN2

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.

TYPE 7136

ADC

LTC1968

VOUT

OUT RTN

1968 TS04

GROUND PIN 6

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 VIOS/VOOS by extrapolating read-

ings > ±5mVDC.

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 5mVRMS to

500mVRMS.

– 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.

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