6

Application Information

Theory Of Operation

The HA-5004 is a high performance amplifier that uses

current feedback to achieve its outstanding performance.

Although it is externally configured like an ordinary op amp

in most applications, its internal operation is significantly

different.

Inside the HA-5004, there is a unity gain buffer from the non-

inverting (+) input to the inverting-input (as suggested by the

circuit symbol), and the inverting terminal is a low

impedance point. Error currents are sensed at the inverting

input and amplified; a small change in input current

produces a large change in output voltage. The ratio of

output voltage delta due to input current delta is the

transimpedance of the device.

Steady state current at the inverting input is very small

because the transimpedance is large. The voltage across

the input terminals is nearly zero due to the buffer amplifier.

These two properties are similar to standard op amps and

likewise simplify circuit analysis.

Resistor Selection

The HA-5004 is optimized for a feedback resistor of 250

regardless of gain configuration. It is important to note that

this resistor is required even for unity gain applications;

higher gain settings use a second resistor like regular op

amp circuits as shown in Figure 2 below.

Power Supplies

The HA-5004 will operate over a wide range of supply

voltages with excellent performance. Supplies may be either

single-ended or split, ranging from 6V (

Appropriate reduction in input and output signal excursion is

necessary for operation at lower supply voltages. Bypass

capacitors from each supply to ground are recommended,

typically a 0.01

electrolytic.

Current Limit

No internal current limiting is provided for the HA-5004 in

order to maximize bandwidth and slew rate. However, power

be used. If required, 100

recommended.

Enable/Disable and Thermal

Overload Operation

The HA-5004 operates normally with a TTL low state on pin

7 (OE) but it may be disabled manually by a TTL high state

at this input. When disabled, the output and inverting-input

go to a high impedance state and the circuit is electrically

debiased, reducing supply current by about 5mA. It is

important to keep the differential input voltage below the

absolute maximum rating of 5V when the device is disabled.

If the power dissipation becomes excessive and chip

automatically disable itself. The thermal overload condition

will be indicated by a low state at the TOL output on pin 10.

(TOL is also low for manual shutdown via pin 7). Automatic

thermal shutdown can be bypassed by a TTL high state on

Thermal Overload Inhibit (TOI) pin 6. See the truth table for a

summary of operation.

Offset Adjustment

Offset voltage may be nulled with a 5k

between pins 3 and 4, center tapped to the positive supply.

Setting the slider towards pin 3 (+BAL) increases output

voltage; towards pin 4 (-BAL) decreases output voltage.

Offset can be adjusted by about

range is extended with a lower resistance potentiometer.

14

13

12

11

10

9

8

1

2

3

4

5

6

7

BAL

+

+5V

-15V

+15V

NC

TOI

GND

OE

THERMAL OVERLOAD

TOL

10k

Ω

5k

Ω

100

100

Ω

249

Ω

249

Ω

+

-

-

HA-5004