APPLICATION NOTES

3

Rev. A

3/03

HEAT SINKING

To determine if a heat sink is necessary for your appli-

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

and governing equation below.

Thermal Model:

Governing Equation:

Where

= Junction Temperature

= Total Power Dissipation

R

θJC

= Junction to Case Thermal Resistance

R

R

= Case Temperature

= Ambient Temperature

= Sink Temperature

Example:

The example demonstrates a worst case analysis for

the op-amp output stage. This occurs when the output

voltage is 1/2 the power supply voltage. Under this con-

dition, maximum power transfer occurs and the output

is under maximum stress.

Conditions:

Ω

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

as an 8 VDC output voltage.

1.) Find driver power dissipation

=(16V-8V) (8V/200

Ω)

=320mW

4.) R

5.) R

6.) Rearrange governing equation to solve for R

R

= (125°C - 100°C)/0.32W - 58°C/W - 0.15°C/W

=78.1 - 58.15

=19.9°C/W

The heat sink in this example must have a thermal

resistance of no more than 19.9°C/W to maintain a junc-

tion temperature of less than +125°C.

INPUT CONSIDERATIONS

An input resistor (RIN below) is required in circuits

where the input to the MSK0024 will be subjected to

transient or continuous voltages exceeding the ±6V

maximum differential limit. This resistor will limit the cur-

rent that can be forced into the bases of the input tran-

sistors.

FEEDBACK RESISTORS

Feedback resistors should be of low enough value

(<5K recommended) to ensure that the time constant

formed with the capacitance at the summing junction

will not limit amplifier performance. If a larger resistor

must be used, a small (< 10pF) feedback capacitor may

be used in parallel with the feedback resistor to compen-

sate and optimize the performance of the MSK0024.

TYPICAL APPLICATION CIRCUIT

POWER SUPPLY BYPASSING

Both the negative and 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 micro-

farad ceramic capacitor in parallel with a 4.7 microfarad

tantalum capacitor from each power supply pin to ground.