APPLICATION NOTES

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.

Governing Equation:

This 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 condition, maximum power transfer oc-

curs and the output is under maximum stress.

Conditions:

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

as an 8VDC output voltage.

1.) Find Driver Power Dissapation

=(16V-8V) (8V/100Ω)

=0.64W

=((125°C -90°C)/0.64W) - 45°C/W - 0.15°C/W

=54.7 - 46.15

=9.5°C/W

Rev. A 4/02

3

Where

be calculated as follows.

Short circuit current limit should be set at least 2X above the

highest normal operating output current to keep the value of RSC low

enough to ensure that the voltage dropped accross the short circuit

current limit resistor doesn't adversely affect normal operation.

INTERNAL FEEDBACK RESISTOR

The MSK 739 is equipped with an internal 1.5KΩ feedback resis-

tor. Bandwidth and slew rate can be optimized by connecting the

MSK 739 as shown in Figure 2. Placing the feedback resistor inside

the hybrid reduces printed circuit board trace length and its'

asscociated capacitance which acts as a capacitive load to the op-

amp output. Reducing the capacitive load allows the output to slew

faster and greater bandwidths will be realized. Refer to Table 1 for

recommended RIN values for various gains.

APPROXIMATE

DESIRED GAIN

VALUE

1.5KΩ

TABLE 1

Whenever the internal resistor is not being used it is good practice

to short pin 4 and 5 to avoid inadvertently picking up spurious sig-

nals.

APPROXIMATE

DESIRED GAIN

RI(+)

RI(-)

Rf(Ext)

Cf

1

-1

249Ω

499Ω

499Ω

2

1

-2

160Ω

249Ω

499Ω

2

1

-5

169Ω

200Ω

1KΩ

2

1

-8

100Ω

124Ω

1KΩ

2

1

90.9Ω

100Ω

1KΩ

2

-20

-10

1

100Ω

100Ω

2KΩ

2

TABLE 2

1 The positive input resistor is selected to minimize any bias current induced offset

voltage.

2 The feedback capacitor will help compensate for stray input capacitance. The value of

-1

-2

-10

750Ω

150Ω

Thermal Model:

OUTPUT SHORT CIRCUIT PROTECTION

The output section of the MSK 739 can be protected from direct

shorts to ground by placing current limit resistors between pins 1

and 12 and pins 9 and 10 as shown in Figure 1.

Recommended External Component Selection

Guide Using External Rf

this capacitor can be dependent on individual applications. A 0.5 to 5pF capacitor is

usually optimum for most applications.

3 Effective load is RL in parallel with Rf.