7

Application Information

Optimum Feedback Resistor

The plots of inverting and non-inverting frequency response,

see Figure 8 and Figure 9 in the typical performance section,

illustrate the performance of the HA5023 in various closed

loop gain configurations. Although the bandwidth

dependency on closed loop gain isn’t as severe as that of a

voltage feedback amplifier, there can be an appreciable

decrease in bandwidth at higher gains. This decrease may

be minimized by taking advantage of the current feedback

All current feedback amplifiers require a feedback resistor,

the internal compensation capacitor, sets the dominant pole

of the frequency response. Thus, the amplifier’s bandwidth is

optimized for a 1000

a unity gain application decreases stability, resulting in

excessive peaking and overshoot. At higher gains the

off of stability for bandwidth.

gains, and the expected bandwidth.

PC Board Layout

The frequency response of this amplifier depends greatly on

the amount of care taken in designing the PC board. The

use of low inductance components such as chip resistors

and chip capacitors is strongly recommended. If leaded

components are used the leads must be kept short

especially for the power supply decoupling components and

those components connected to the inverting input.

Attention must be given to decoupling the power supplies. A

large value (10

µF) tantalum or electrolytic capacitor in

parallel with a small value (0.1

µF) chip capacitor works well

in most cases.

A ground plane is strongly recommended to control noise.

Care must also be taken to minimize the capacitance to

ground seen by the amplifier’s inverting input (-IN). The

larger this capacitance, the worse the gain peaking, resulting

in pulse overshoot and possible instability. It is

recommended that the ground plane be removed under

traces connected to -IN, and that connections to -IN be kept

as short as possible to minimize the capacitance from this

node to ground.

Driving Capacitive Loads

Capacitive loads will degrade the amplifier’s phase margin

resulting in frequency response peaking and possible

oscillations. In most cases the oscillation can be avoided by

placing an isolation resistor (R) in series with the output as

shown in Figure 6.

The selection criteria for the isolation resistor is highly

dependent on the load, but 27

Ω has been determined to be

a good starting value.

Power Dissipation Considerations

Due to the high supply current inherent in dual amplifiers, care

must be taken to insure that the maximum junction

exceeded. Figure 7 shows the maximum ambient temperature

versus supply voltage for the available package styles (Plastic

DIP, SOIC). At

take into account output power, be performed by the designer.

GAIN

BANDWIDTH

(MHz)

-1

750

100

+1

1000

125

+2

681

95

+5

1000

52

+10

383

65

-10

750

22

+

-

R

FIGURE 6. PLACEMENT OF THE OUTPUT ISOLATION

RESISTOR, R

100

Ω

5

7

9

11

13

15

140

130

120

110

100

90

80

SUPPLY VOLTAGE (

±V)

PDIP

SOIC

50

60

70

FIGURE 7. MAXIMUM OPERATING AMBIENT TEMPERATURE

vs SUPPLY VOLTAGE

HA5023