2-617

HFA-0002

Applications Information

Offset Voltage Adjustment

The HFA-0002, due to its low offset voltage, will typically not

require any external offset adjustment. If certain applications

do require lower offset, the following diagram shows one

possible configuration.

FIGURE 29.

The power supply lines must be well decoupled to filter any

power supply noise. A 20K trim pot will allow an offset

adjustment of about 3mV, referred to input.

PC Board Layout Guidelines

When designing with the HFA-0002, good high frequency

(RF) techniques should be used when doing pc board

layouts. A massive ground plane should be used to maintain

a low impedance ground. PC board traces should be kept as

short as possible and kept wide to minimize trace inductance

and impedance. Stray capacitance at the op amps output

and at the high impedance inputs should be kept to a

minimum, to prevent any unwanted phase shift and band-

width limiting.

When breadboarding remember to keep feedback resistor

values low (

≤5kΩ) for optimum performance. The use of

metal film resistors for values over 200

Ω and carbon film

resistors under 200

Ω typically gives the best performance.

Remember to keep all lead lengths as short as possible to

minimize lead inductance.

Sockets will add parasitic capacitance and inductance and

therefore can limit AC performance as well as reduce

stability. If sockets must be used, a low profile socket with

minimum pin to pin capacitance will minimize any perfor-

mance degradation.

Power supply decoupling is essential for high frequency op

amps. A 0.01

µF high quality ceramic capacitor at each

supply pin in parallel with a 1

µF tantalum capacitor will pro-

vide excellent decoupling. Chip capacitors produce the best

results due to the ease of placement next to the op amp and

they have negligible lead inductance. If leaded capacitors

are used, again the lead lengths should be kept to a

minimum.

Saturation Recovery

When an op amp is over driven output devices can saturate

and sometime take a long time to recover. By clamping the

input to safe levels, output saturation can be avoided. If

output saturation cannot be avoided, the recovery time for

an input sine wave at 25% overdrive is 100ns.

+5V

+

1

2

3

4

5

6

7

20K

5V

-