MSK171B Просмотр технического описания (PDF) - M.S. Kennedy

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MSK171B

HIGH POWER DUAL OPERATIONAL AMPLIFIER

M.S. Kennedy 

APPLICATION NOTES

SAFE OPERATING AREA (SOA)

AMPLIFIER STABILITY

Since both output transistors in this amplifier are NPN, con-

sideration must be taken when stabilizing the output. A one

ohm resistor, 0.1uF capacitor snubber network has been added

internally from the output to -Vcc on each amplifier. This con-

figuration minimizes local output stage oscillations. As always,

adequate power supply bypassing is a necessity for ampli-

fier stability. A parallel combination of a 4.7uF electrolytic (for

every amp of output current) and a 0.01uF ceramic disc capaci-

tor should be connected as close as possible to the package

power supply pins to ground. The R-C snubber networks shown

on the outputs of the amplifiers in the typical circuits are inter-

nal and should not be added externally.

Safe operating area curves are a graphical representation of

all of the power limiting factors involved in the output stage of

an operational amplifier. Three major power limiting factors

are; output transistor wire bond carrying capability, output tran-

sistor junction temperature and secondary breakdown effects.

To see if your application is meeting or exceeding the limita-

tions of the safe operating area curves, perform the following

steps:

1.) Find the worst case output power dissipation. For a split

supply, purely resistive load application, this occurs when

VOUT=1/2 VCC.

2.) Take the values of (VCC-VOUT) and the corresponding out-

put current and find their intersection on the safe operating

area curves.

3.) Verify this point is below the safe operating area curves.

This is a simple task for purely resistive loads, for reactive loads

the following table will save extensive analysis. Under tran-

sient conditions, capacitive and inductive loads up to the fol-

lowing maximum are safe.

±Vcc

20V

15V

10V

5V

Capacitive Load

200uF

500uF

5mF

50mF

Inductive Load

7.5mH

25mH

35mH

150mH

If the inductive load is driven near steady state conditions al-

lowing the output to drop more than 6V below the supply rail

while the amplifier is current limiting, the inductor should be

capacitively coupled or the supply voltage must be lowered to

meet the SOA criteria. It is a good practive to also connect

reverse biased fast recovery diodes to the output for protection

against sustained high energy flyback.

3

PARALLEL CONNECTION

(yields single 6A amplifier)

BIDIRECTIONAL MOTOR DRIVE

Rev. C 8/00

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