13

LT1787/LT1787HV

1787fc

Adjusting Gain Setting

The LT1787 may be used in all operating modes with an

S

0

0.30

0.25

0.20

0.15

0.10

0.05

0

0.005 0.010

IDEAL

0.015 0.020

1787 F09

0.025 0.030

Figure 9. Expanded Scale of Unidirectional Output

LT1787’s transconductance, 400

µA/V typical. A nominal

gain of 40 may be obtained with an external 100k resistor

The transconductance gm is set by on-chip resistors on

the LT1787. These resistors match well but have loose

absolute tolerance. This will normally require that the

external gain setting resistor be trimmed for initial accu-

racy. After trimming, the temperature stability of the gm

and therefore gain will be –200ppm/

°C.

The only limitations placed upon the resistor choice is care

must be taken not to saturate the internal circuitry by