icl7650csdt Maxim Integrated Products, Inc., icl7650csdt Datasheet - Page 8

• Manufacturer Part Number: icl7650csdt
• Description: Chopper-stabilized Op Amps
• Manufacturer: Maxim Integrated Products, Inc.

Chopper-Stabilized Op Amps
Low-leakage, high-impedance CMOS inputs allow the
ICL7650/ICL7653 to measure high-impedance sources.
Stray leakage paths can decrease input resistance and
increase input currents unless inputs are guarded.
Boards must be thoroughly cleaned with TCE or alcohol
and blown dry with compressed air. The board should
be coated with epoxy or silicone after cleaning to pre-
vent contamination.
Leakage currents may cause trouble even with properly
cleaned and coated boards, particularly since the input
pins are adjacent to pins that are at supply potentials.
Leakage can be significantly reduced by using guard-
Figure 3. Input Guard Connection
8
_______________________________________________________________________________________
NOTE:
*
USE R3 TO COMPENSATE FOR LARGE
SOURCE RESISTANCES, OR FOR CLAMP
OPERATION (FIGURE 5).
R1 + R2
R1 R2
INPUT
R1
SHOULD BE LOW IMPEDANCE FOR
OPTIMUM GUARDING.
R1
R3*
INPUT
R3*
NONINVERTING AMPLIFIER
INVERTING AMPLIFIER
Input Guarding
R2
R2
OUTPUT
OUTPUT
ing to decrease the voltage difference between inputs
and adjacent metal runs. Use a 10-lead pin circle, with
the leads of the device formed so that the holes adja-
cent to the inputs are empty when it is inserted in the
board to accomplish input guarding of the 8-pin TO-99
package. A conductive ring surrounding the inputs, the
“guard,” is connected to a low-impedance point that is
approximately the same voltage as the inputs. The
guard then absorbs the leakage current from the high-
voltage pins. Typical guard connections are shown in
Figure 3.
INPUT
BOARD LAYOUT FOR INPUT GUARDING
WITH TO-99 PACKAGE.
CAPACITORS
EXTERNAL
OUTPUT
R3*
V+
BOTTOM VIEW
V-
FOLLOWER
GUARD
6
5
7
4 3
CAPACITORS
EXTERNAL
8
1
2
OUTPUT