Apex Digital PA40 - Manual (Page 4)

APEX MICROTECHNOLOGY CORPORATION • 5980 NORTH SHANNON ROAD • TUCSON, ARIZONA 85741 • USA • APPLICATIONS HOTLINE: 1 (800) 546-2739
OPERATING
CONSIDERATIONS
PA40
GENERAL
Please read Application Note 1 "General Operating
Considerations" which covers stability, supplies, heat sinking,
mounting, current limit, SOA interpretation, and specifi cation
interpretation. Visit www.apexmicrotech.com for design tools
that help automate tasks such as calculations for stability,
internal power dissipation, current limit; heat sink selection;
Apex’s complete Application Notes library; Technical Seminar
Workbook; and Evaluation Kits.
INPUT PROTECTION
The PA40 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 insuffi cient
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.
STABILITY
The PA40 has suffi cient 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 PA40 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 250V working voltage. The compensation
capacitor and associated resistor R
C
must be mounted closely
to the amplifi er pins to avoid spurious oscillation. An NPO
capacitor is recommended for compensation.
This data sheet has been carefully checked and is believed to be reliable, however, no responsibility is assumed for possible inaccuracies or omissions. All specifi cations are subject to change without notice.
PA40U REV. B JUNE 2001 © 2001 Apex Microtechnology Corp.
10 20 30 50 100 200 300 500
OUTPUT CURRENT FROM +V
S
OR –V
S
, (mA)
2
3
4
5
10
20
30
40
50
100
PA40 SOA
200mS
120
200
DC, T
C = 85
°
C
300mS
DC, T
C = 25
°
C
SAFE OPERATING AREA (SOA)
The MOSFET output stage of this power operational
amplifi er 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
fl yback. However, for protection against sustained, high energy
fl yback, external fast-recovery diodes should be used.