HEAT SINKING

To determine if a heat sink is necessary for your application

and if so, what type, refer to the thermal model and governing

equation below.

Example:

This example demonstrates a worst case analysis for the buffer

output stage. This occurs when the output voltage is 1/2 the

power supply voltage. Under this condition, maximum power

transfer occurs and the output is under maximum stress.

Conditions:

Ω

Governing Equation:

Where

R

R

R

R

= ((125°C - 80°C) / .64W) - 65°C/W - .15°C/W

= 70.3 - 65.15

= 5.2°C/W

The heat sink in this example must have a thermal resistance

of no more than 5.2°C/W to maintain a junction temperature of

no more than +125°C.

Thermal Model:

For a worst case analysis we will treat the ±8Vp sine wave

as an 8 VDC output voltage.

1.) Find Driver Power Dissipation

= (16V-8V) (8V/100

Ω)

= 640mW

4.) R

5.) R

6.) Rearrange governing equation to solve for R

θSA

POWER SUPPLY BYPASSING

Both the negative and the positive power supplies must be

effectively decoupled with a high and low frequency bypass

circuit to avoid power supply induced oscillation. An effective

decoupling scheme consists of a 0.1 microfarad ceramic ca-

pacitor in parallel with a 4.7 microfarad tantalum capacitor from

each power supply pin to ground.

APPLICATION NOTES

OFFSET VOLTAGE ADJUST

See Figure 1. To externally null the offset voltage, connect a

200

Ω potentiometer between Pins 7 and 10 and leave Pin 6

open. If offset null is not necessary, short Pin 6 to Pin 7 and

remove the 200

Ω potentiometer. Do not connect Pin 7 to -

Vcc.

CURRENT LIMITING

See Figure 1. If no current limit is required, short Pin 1 to Pin

12 and Pin 9 to Pin 10 and delete Q1 thru Q4 connections. Q1

through Q4 and the Rlim resistors form a current source current

limit scheme and current limit resistor values can be calculated

as follows:

+Rlim

≅ Vbe

-Rlim

≅ Vbe

Isc

Isc

Since current limit is directly proportional to the base-emitter

voltage drop of the 2N2222's and 2N2907's in the current

limit scheme, the current limit value will change slightly with

ambient temperature changes. The base-emitter voltage drop

will decrease as temperature increases causing the actual cur-

rent limit point to decrease.

3

Rev. D 9/06