PA91 データシートの表示（PDF） - Cirrus Logic

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PA91

High Voltage Power Operational Amplifiers

Cirrus Logic 

®

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PA91

SAFE OPERATING AREA (SOA)

The MOSFET output stage of this power operational

500

amplifier has two distinct limitations:

1. The current handling capability of the MOSFET ge-

300

ometry and the wire bonds.

2. The junction temperature of the output MOSFETs.

200

NOTE: The output stage is protected against transient

flyback. However, for protection against sustained, high

energy flyback, external fast-recovery diodes should be

100

used.

SAFE OPERATING CURVES

50

The safe operating area curves define the maximum

additional internal power dissipation the amplifier can

30

tolerate when it produces the necessary output to drive

an external load.

20

SOA

200mS

100mS

DC, T

DC, T

C = 25°C

DC, T

C = 85°C

C = 125°C

INPUT PROTECTION

Although the PA91 can withstand differential voltages

PULSE CURVES @ 10% DUTY CYCLE MAX.

10

25

50 75 100 125

250

500

up to ±20V, additional external protection is recom-

mended. Low leakage, low capacitance JFETs con-

SUPPLY TO OUTPUT DIFFERENTIAL, VS - VO (V)

nected as diodes are recommended (e.g. 2N4416, Q1-Q4 in Figure

2). The differential input voltage will be clamped to ±1.4V. This is

+VS

sufficient overdrive to produce maximum power bandwidth.

Z1

POWER SUPPLY PROTECTION

Unidirectional zener diode transient suppressors are recommended

as protection on the supply pins. See Figure 2. 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 per-

–IN

Q1

Q2

+IN

1

11, 12

Q3

6

PA91

Q4

2

7, 8

formance including power-on overshoot and power-off polarity rever-

sals 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. Re-

FIGURE 2.

OVERVOLTAGE

PROTECTION

Z2

–VS

versals 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 PA91 is externally compensated and performance can be tailored to the application. Use the graphs of small

signal response and power response as a guide. The compensation capacitor CC must be rated at 500V working

voltage. An NPO capacitor is recommended. The compensation network CCRC must be mounted closely to the

amplifier pins 4 and 5 to avoid spurious oscillation.

QUIESCENT CURRENT REDUCTION

When pin 3 (IQ) is shorted to pin 5 (CC2) the AB biasing of the output stage is disabled. This raises distortion since

the output stage is then class C biased, but reduces the quiescent current by 1mA for a power dissipation savings

of 0.4W. Pin 3 may be left open if not used.

PA91U

5

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