REV. 1A January 2004

5

KH104

DATA SHEET

voltage across the regulator of 3.6V and a minimum

regulator current of 10mA will satisfy the regulator

dropout voltage and current limits.

Given the maximum anticipated power supply voltages,

the shunt resistor should be calculated to yield a 35mA

current from that voltage to the regulated voltage of 5.4V.

This will leave 10mA through the regulator at the

minimum quiescent current of 45mA. The regulator input

voltages may be reduced directly by dropping the voltage

supplies, or, if that option is not available, using either

a zener or resistive dropping element in series with

the supply.

If a series dropping element is used, the

decoupling capacitors must appear on pins 1 and 2 of the

KH104. Figure 3 shows two possible power reduction

circuits from fixed ±15V supplies.

Several methods of decreasing the thermal resistance

from case to ambient are possible. With no heat paths

other than still air at 25°C, the thermal resistance from

case to ambient for the KH104 is about 40°C/W. When

placed in a printed circuit board with all ground pins

soldered into a ground plane 1” X 1.5”, the thermal

resistance drops to about 30°C/W In this configuration,

the case rise will be 30°C for 9V supplies and 50°C

for 16V supplies.

This results in maximum allowable

ambient temperatures of 110°C and 90°C, respectively. If

higher operating temperatures are required, heat sinking

of the package is recommended.

Figure 3: Reducing Power Dissipation

the op amp loses influence and the KH104 gain and

output impedance dominate. To ensure a smooth

Since the KH104 has a 50

Ω output impedance, its

output voltage is a function of the load impedance

ite amplifier at low frequencies and DC is relatively

independent of the load impedance, due to the high

open-loop gain of the op amp.

Thus, to avoid gain

mismatching and phase non-linearity, use the composite

amplifier only if the load impedance is constant from DC

Use of a composite amplifier reduces input offset voltage

and its corresponding drift, but has no effect on input bias

current. This current is converted to an input voltage by

the resistance to ground seen at the amplifier input and

the voltage appears, amplified, at the output.

Typical

input offset voltage due to the bias current is 2mV and

input offset drift is approximately 15mV/°C.

Thermal Considerations

The KH104 case must be maintained at or below 140°C.

Note that because of the amplifier design, power dissipa-

tion remains fairly constant, independent of the load or

drive level. Therefore, standard derating is not possible.

There are two ways to keep the case temperature low.

The first is to keep the amount of power dissipated inside

the package to a minimum and the second is to get the

heat out of the package quickly by reducing the thermal

resistance from case to ambient.

A large portion of the heat dissipated inside the package

is in the voltage regulators. At the minimum +9V supply

level the regulators dissipate 390mW and at the

maximum ±16V supply level they dissipate 1.2W.

The amplifier itself dissipates a fairly constant 600mW

(55mA x 10.8V). Reducing the power dissipation of the

internal regulators will go far towards reducing the

internal junction temperatures without impacting the so

performance. Reducing either the input supply voltages

(on pins 1 and 2) and/or shunting the regulator current

through external resistors (from pins 1 to 14 and pins

2 to 13) are both effective means towards significantly

reducing the internal power dissipation. A minimum

2.2

µF

0.01

µF

115

Ω

D1

5.6V

+15V

2.2

µF

0.01

µF

115

Ω

D2

5.6V

-15V

1

2

13

14

+

+

2.2

µF

0.01

µF

200

Ω

+15V

2.2

µF

0.01

µF

200

Ω

-15V

1

2

13

14

+

+

60

Ω

60

Ω

D1, D2 IN4734

– 760mW

– 900mW