Considerations" which covers stability, supplies, heat sinking,
mounting, current limit, SOA interpretation, and specification
interpretation. Visit www.apexmicrotech.com for design tools
that help automate tasks.
OPERATING
CONSIDERATIONS
heatsink on the backside of the FR4/PC board, or copper
slug. Do not allow the temperature to exceed 85°C. The
heatslug is tied internally to -V
S
.
EQUIVALENT SCHEMATIC
3
INPUT PROTECTION
The PA140 inputs are protected against common mode
voltages up the supply rails and differential voltages up to
±16 volts as well as static discharge. Differential voltages
exceeding 16 volts will be clipped by the protection circuitry.
However, if more than a few milliamps of current is available
from the overload source, the protection circuitry could be
destroyed. The protection circuitry includes 300 ohm current
limiting resistors at each input, but this may be insufficient
for severe overloads. It may be necessary to add external
resistors to the application circuit where severe overload
conditions are expected. Limiting input current to 1mA will
prevent damage.
Q1
D1
Q2
Q3
Q4
1
+V
S
I
OUT
5
Q5
6
Q6
–IN
D2
2
COMP
D3
D4
D5
COMP Q8
7
+IN
Q11
Q12
Q13
Q10
Q14
–V
S
4
STABILITY
The PA140 has sufficient phase margin when compensated
for unity gain to be stable with capacitive loads of at least 10
nF. However, the low pass circuit created by the sumpoint
(–in) capacitance and the feedback network may add phase
shift and cause instabilities. As a general rule, the sumpoint
load resistance (input and feedback resistors in parallel)
should be 1K ohm or less at low gain settings (up to 10).
Alternatively, use a bypass capacitor across the feedback
resistor. The time constant of the feedback resistor and bypass
capacitor combination should match the time constant of the
sumpoint resistance and sumpoint capacitance.
The PA140 is externally compensated and performance
can be tailored to the application. Use the graphs of small
signal gain and phase response as well as the graphs for
slew rate and power response as a guide. The compensation
capacitor C
C
must be rated at 350V. The compensation
capacitor and associated resistor R
C
must be mounted closely
to the amplifier pins to avoid spurious oscillation. An NPO
capacitor is recommended for compensation. The PA140
monolithic amplifier uses an all NMOS output topology that
presents a special stability problem. An output snubber
network of 330pF and 100Ω in series from the output to –V
S
will eliminate this problem. This network is not required if the
load capacitance is greater than 330pF.
SUB
SAFE OPERATING AREA (SOA)
The MOSFET output stage of this power operational
amplifier has two distinct limitations:
1. The current handling capability of the die metallization.
2. The temperature of the output MOSFETs.
NOTE: The output stage is protected against transient
flyback. However, for protection against sustained, high energy
flyback, external fast-recovery diodes should be used.
PA140 SOA
200mS
300mS
200
OUTPUT CURRENT FROM +V
S
OR –V
S
, (mA)
120
100
50
40
30
20
DC
,T
DC
C
=
,T
C=
85
°
C
25
°
C
10
MOUNTING
The PA140CC 7-pin DDPAK surface mountable package
has a large exposed integrated copper heatslug to which
the monolithic amplifier is directly attached. The PA140CC
requires surface mount techniques of heatsinking. A solder
connection to an area of 1 to 2 square inches of foil is
recommended for circuit board layouts. This may be adequate
heatsinking but the large number of variables involved
suggests temperature measurements to be made on the top
of the package. Surface mount techniques include the use
of a surface mount fan in combination with a surface mount
5
4
3
2
10
20
30
50
100
200 300
500
APPLICATION REFERENCES:
For additional technical information please refer to the
following Application Notes:
AN 01: General Operating Considerations
AN 25: Driving Capacitive Loads
AN 38: Loop Stability with Reactive Loads
This data sheet has been carefully checked and is believed to be reliable, however, no responsibility is assumed for possible inaccuracies or omissions. All specifications are subject to change without notice.
京公网安备 11010802033920号
EEWORLD
