6

FN2856.6

November 19, 2004

Application Information

Offset Adjustment

The offset voltage of the HA-2420 and HA-2425 may be

adjusted using a 100k

Ω trim pot, as shown in Figure 8. The

recommended adjustment procedure is:

Apply 0V to the sample-and-hold input, and a square wave

to the S/H control.

Adjust the trim pot for 0V output in the hold mode.

Gain Adjustment

The linear variation in pedestal voltage with sample-and-hold

some applications (D/A deglitcher, A/D converter) the gain

error can be adjusted elsewhere in the system, while in other

applications it must be adjusted at the sample-and-hold. The

two circuits shown below demonstrate how to adjust gain

error at the sample-and-hold.

The recommended procedure for adjusting gain error is:

1. Perform offset adjustment.

2. Apply the nominal input voltage that should produce a

+10V output.

3. Adjust the trim pot for +10V output in the hold mode.

4. Apply the nominal input voltage that should produce a

-10V output.

the trim pot for an output hold voltage of

Figure 8 shows a typical unity gain circuit, with Offset

Zeroing. All of the other normal op amp feedback

configurations may be used with the HA-2420, HA-2425. The

input amplifier may be used as a gated amplifier by utilizing

Pin 11 as the output. This amplifier has excellent drive

capabilities along with exceptionally low switch leakage.

The method used to reduce leakage paths on the PC board

and the device package is shown in Figure 9. This guard ring

is recommended to minimize the drift during hold mode.

The hold capacitor should have extremely high insulation

resistance and low dielectric absorption. Polystyrene (below

For more applications, consult Intersil Application Note

AN517, or the factory applications group.

0

+10

5

-5

-10

-15

-20

-25

-30

-35

-10

-5

+5

+10

DC INPUT VOLTAGE (V)

HOLD STEP VOLTAGE (mV)

FIGURE 5. HOLD STEP vs INPUT VOLTAGE

V

10

–

NOMINAL

()

-10V

()

+

2

-----------------------------------------------------------------

-IN

+IN

OUT

S/H

CONTROL

OUTPUT

INPUT

S/H CONTROL INPUT

NOTE:

GAIN

RF

–

RI

-----------

∼

FIGURE 6. INVERTING CONFIGURATION

+IN

-IN

OUT

S/H

CONTROL

OUTPUT

INPUT

S/H CONTROL

INPUT

NOTE:

GAIN ~ 1

RF

RI

--------

+

FIGURE 7. NON-INVERTING CONFIGURATION

IN

V-

100k

Ω

OFFSET TRIM (

±25mV RANGE)

OUT

V+

CONTROL

-

+

-

+

FIGURE 8. BASIC SAMPLE-AND-HOLD (TOP VIEW)

HA-2420, HA-2425