MSK801 datasheet(3/6 Pages) MSK

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APPLICATION NOTES

Heat Sinking

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

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

governing equation below.

Governing Equation:

Example:

This example demonstrates a worst case analysis for

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

age is 1/2 the power supply voltage. Under this condition,

maximum power transfer occurs and the output is under

maximum stress.

Conditions:

VCC=±16VDC

VO=±8Vp Sine Wave, Freq.=1KHz

RL=100

Ω

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

wave as an 8VDC output voltage.

1.) Find Driver Power Dissapation

PD=(VCC-VO) (VO/RL)

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

Ω)

0.64W

2.) For conservative design, set TJ=+125°C

3.) For this example, worst case TA=+50°C

4.) R

θJC=65°C/W from MSK 801 Data Sheet

5.) R

θCS=0.15°C/W for most thermal greases

6.) Rearrange governing equation to solve for R

θSA

Rev. C 8/05

TJ=PD x (R

θJC + RθCS + RθJC) + TA

Where

TJ=Junction Temperature

PD=Total Power Dissipation

θJC=Junction to Case Thermal Resistance

θCS=Case to Heat Sink Thermal Resistance

θSA=Heat Sink to Ambient Thermal Resistance

TC=Case Temperature

TA=Ambient Temperature

TS=Sink Temperature

Thermal Model:

APPROXIMATE

DESIRED GAIN

RI(+)

RI(-)

-1

500

Ω

0.01µf

Ω

0.01µf

Ω

910

Ω

3.6K

Ω

120

Ω 0.01µf

910

Ω

10K

Ω

150

Ω 0.01µf

+10

-10

Ω

9.1K

Ω

150

Ω 0.01µf

Recommended External Component Selection

Guide Using External Rf

-5

820

Ω

4.99K

Ω 120Ω 0.01µf

1 The positive input resistor is selected to minimize offset

currents. The positve input can be grounded without a

resistor if desired.

2 This feedback capacitor will help compensate for stray

input capacitance. The value of this capacitor can be

dependent on individual applications. A 2 to 9 pf capacitor

is usually optimum for most applications.

Load Considerations

When determining the load an amplifier will see, the

capacative portion must be taken into consideration. For

an amplifier that slews at 1000V/µS, each pf will require 1

mA of output current. To minimize ringing with highly

capacitive loads, reduce the load time constant by adding

shunt resistance.

Case Connection

The MSK 801 has pin 8 internally connected to the

case. The case is not electrically connected to the internal

circuit. Pin 8 should be tied to a ground plane for shielding.

For special applications, consult factory.

θSA=((TJ-TA)/PD) - (RθJC) - (RθCS)

((125°C -50°C)/0.64W) - 65°C/W - 0.15°C/W

117.2 - 65.15

52.0°C/W

Stability and Layout Considerations

As with all wideband devices, proper decoupling of the

power lines is extremely important. The power supplies

should be bypassed as near to pins 10 and 12 as possible

with a parallel grouping of a 0.01µf ceramic disc and a 4.7µf

tantalum capacitor. Wideband devices are also sensitive

to printed circuit board layout. Be sure to keep all runs as

short as possible, especially those associated with the sum-

ming junction, power lines and compensation pins.

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