PA90_10 Datasheet, PDF (5/6 Pages) Cirrus Logic – High Voltage Power Operational Amplifiers

®
Product Innovation From
PA90
SAFE OPERATING AREA (SOA)
The MOSFET output stage of this power operational amplifier 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.
NOTE: The output stage is protected against transient flyback. However, for protection against sustained, high en-
ergy flyback, external fast-recovery diodes should be used.
SAFE OPERATING CURVES
The safe operating area curves define the maximum ad-
500
ditional internal power dissipation the amplifier can toler-
ate when it produces the necessary output to drive an
300
external load.
200
INPUT PROTECTION
Although the PA90 can withstand differential voltages up
to ±20V, additional external protection is recommended.
100
Low leakage, low capacitance JFETs connected as di-
odes are recommended (e.g. 2N4416, Q1-Q4 in Fig-
ure 2). The differential input voltage will be clamped to
50
±1.4V. This is sufficient overdrive to produce maximum
power bandwidth.
30
SOA
200mS
100mS
DC, _T
DC, _T
C _{= 25°C}
DC, _T
C _{= 85°C}
C _{= 125°C}
POWER SUPPLY PROTECTION
20
Unidirectional zener diode transient suppressors are
recommended as protection on the supply pins. See
Figure 2. The zeners clamp transients to voltages within
PULSE CURVES @ 10% DUTY CYCLE MAX.
10
25
50 75 100 125
250
500
the power supply rating and also clamp power supply
reversals to ground. Whether the zeners are used or not,
SUPPLY TO OUTPUT DIFFERENTIAL, V_S - V_O (V)
the system power supply should be evaluated for transient performance
+V_S
including power-on overshoot and power-off polarity reversals as well as
Z1
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.
–IN
Q1
1
11, 12
Q3
6
PA90
Unidirectional transzorbs prevent this, and it is desirable that they be
Q2
Q4
both electrically and physically as close to the amplifier as possible.
+IN
2
7, 8
STABILITY
The PA90 is externally compensated and performance can be tailored
to the application. Use the graphs of small signal response and power
FIGURE 2.
OVERVOLTAGE
PROTECTION
Z2
–V_S
response as a guide. The compensation capacitor C_C must be rated at 500V working voltage. An NPO capacitor
is recommended. The compensation network C_CR_C must be mounted closely to the amplifier pins 4 and 5 to avoid
spurious oscillation.
QUIESCENT CURRENT REDUCTION
When pin 3 (I_Q) 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.
PA90U
5