AD8553

Rev. A | Page 13 of 20

MAXIMIZING PERFORMANCE THROUGH PROPER

LAYOUT

To achieve the maximum performance of the AD8553, care

should be taken in the circuit board layout. The PC board

surface must remain clean and free of moisture to avoid leakage

currents between adjacent traces. Surface coating of the circuit

board reduces surface moisture and provides a humidity barrier,

reducing parasitic resistance on the board.

Care must be taken to minimize parasitic capacitance on Pin 1

and Pin 10 (Resistor R1 connections). Traces from Pin 1 and

Pin 10 to R1 should be kept short and symmetric. Excessive

capacitance on these pins will result in a gain error. This effect

is most prominent at low gains (G < 10).

For high impedance sources, the PC board traces from the

AD8553 inputs should be kept to a minimum to reduce input

bias current errors.

POWER SUPPLY BYPASSING

The AD8553 uses internally generated clock signals to perform

the autocorrection. As a result, proper bypassing is necessary to

achieve optimum performance. Inadequate or improper bypassing

of the supply lines can lead to excessive noise and offset voltage.

A 0.1 μF surface-mount capacitor should be connected between

the supply lines. This capacitor is necessary to minimize ripple

from the correction clocks inside the IC. For dual-supply

operation (see Figure 33), a 0.1 μF (ceramic) surface-mount

capacitor should be connected from each supply pin to ground.

For single-supply operation, a 0.1 μF surface-mount capacitor

should be connected from the supply line to ground.

All bypass capacitors should be positioned as close to the DUT

supply pins as possible, especially the bypass capacitor between

the supplies. Placement of the bypass capacitor on the back of

the board directly under the DUT is preferred.

INPUT OVERVOLTAGE PROTECTION

All terminals of the AD8553 are protected against ESD. In the

case of a dc overload voltage beyond either supply, a large

current would flow directly through the ESD protection diodes.

If such a condition should occur, an external resistor should be

used in series with the inputs to limit current for voltages

beyond the supply rails. The AD8553 can safely handle 5 mA of

continuous current, resulting in an external resistor selection of

CAPACITIVE LOAD DRIVE

The output buffer, Pin 4, can drive capacitive loads up to 100 pF.

I

I

M2

M3

M4

M1

R1

R1

2I

2I

M5

M6

C2

R2

A1

R1

2R2

EXTERNAL

Figure 30. Simplified AD8553 Schematic