PA88 データシートの表示（PDF） - Cirrus Logic

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PA88

High Voltage Power Operational Amplifiers

Cirrus Logic 

PA88 • PA88A

Product Innova tionFrom

GENERAL

Please read Application Note 1 "General Operating Con-

siderations" which covers stability, supplies, heat sinking,

mounting, current limit, SOA interpretation, and specification

interpretation. Visit www.Cirrus.com for design tools that help

automate tasks such as calculations for stability, internal power

dissipation, current limit; heat sink selection; Apex Precision

Power’s complete Application Notes library;Technical Seminar

Workbook; and Evaluation Kits.

CURRENT LIMIT

For proper operation, the current limit resistor (RCL) must be

connected as shown in the external connection diagram. The

minimum value is 3.5 ohm, however for optimum reliability the

resistor value should be set as high as possible. The value

is calculated as follows; with the maximum practical value of

150 ohms.

RCL

=  .7     

ILIM

SAFE OPERATING AREA (SOA)

The MOSFET output stage of this power operational ampli-

fier has two distinct limitations:

1. The current handling capability of the MOSFET geometry

and the wire bonds.

2. The junction temperature of the output MOSFETs.

SOA

250

150

100

DC,

200m1S00mS

T

50

DC, T

C = 25°C

DC, T

C = 85°C

25

C = 125°C

15

10

PULSE CURVES @ 10% DUTY CYCLE MAX

5

25

50 75 100 125

250

500

SUPPLY TO OUTPUT DIFFERENTIAL, VS –VO (V)

NOTE: The output stage is protected against transient flyback.

However, for protection against sustained, high energy flyback,

external fast-recovery diodes should be used.

INPUT PROTECTION

Although the PA88 can withstand differential input voltages

up to ±25V, additional external protection is recommended,

and required at total supply voltages above 300 volts. In most

applications 1N4148 or 1N914 signal diodes are sufficient (D1,

D2 in Figure 2a). In more demanding applications where low

leakage or low capacitance are of concern 2N4416 or 2N5457-

2N5459 JFETs connected as diodes will be required (Q1, Q2

in Figure 2b). In either case the input differential voltage will

be clamped to ±.7V. This is sufficient overdrive to produce

maximum power bandwidth.

POWER SUPPLY PROTECTION

Unidirectional zener diode transient suppressors are recom-

mended as protection on the supply pins. The zeners clamp

transients to voltages within the power supply rating and also

clamp power supply reversals to ground. Whether the zeners

are used or not, the system power supply should be evaluated

for transient performance including power-on overshoot and

power-off polarity reversal as well as line regulation.

Conditions which can cause open circuits or polarity reversals

on either power supply rail should be avoided or protected

against. Reversals or opens on the negative supply rail is

known to induce input stage failure. Unidirectional transzorbs

prevent this, and it is desirable that they be both electrically

and physically as close to the amplifier as possible.

STABILITY

The PA88 has sufficient phase margin to be stable with

most capacitive loads at a gain of 4 or more, using the rec-

ommended phase

compensation.

a.

+VS

The PA88 is exter-

Z1

nally compensated

and performance can

be tailored to the –IN

5

3

application. Use the

graphs of small signal

D1

D2 PA88

response and power +IN

response as a guide.

4

6

The compensation

capacitor CC must

be rated at 500V

working voltage. An b.

NPO capacitor is

Z2

–VS

+VS

recommended. The

Z1

compensation net-

work CCRC must be

mounted closely to

–IN

5

3

the amplifier pins 7 Q1

Q2 PA88

and 8 to avoid spuri- +IN

ous oscillation.

4

6

Z2

–VS

FIGURE 2. OVERVOLTAGE PROTECTION

4

PA88U

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