Apex Digital manual General Input Protection, Stability, Safe Operating Area SOA, PA40 SOA

PA40	OPERATING
	CONSIDERATIONS

GENERAL

Please read Application Note 1 "General Operating 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 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 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.

STABILITY

The PA40 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 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 CC must be rated at 250V working voltage. The compensation capacitor and associated resistor RC must be mounted closely to the amplifier pins to avoid spurious oscillation. An NPO capacitor is recommended for compensation.

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.

PA40 SOA

	200
(mA)	120						200mS
					300mS
	100
,
S
–V
OR	50				DC,		DC,
	40
S								T
+V						T		C
	30						C=	=
FROM							85	25
								°
								C
							°
	20						C
CURRENT	10
OUTPUT	5
	4
	3
	2	20	30	50	100		200	300	500
	10

APEXThis dataMICROTECHNOLOGYsheet has been carefully checkedCORPORATIONand is believed• 5980to be reliable,NORTHhowever,SHANNONno responsibilityROAD •isTUCSON,assumed forARIZONApossible inaccuracies85741 or• omissionsUSA • .APPLICATIONSAll specifications areHOTLINE:subject to change1 (800)without546notice-2739.

PA40U REV. B JUNE 2001 © 2001 Apex Microtechnology Corp.