PA92 Datasheet, PDF (5/6 Pages) Cirrus Logic – HIGH VOLTAGE POWER OPERATIONAL AMPLIFIER

Product Innova tionFrom
PA92
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.cirrus.com for design tools
that help automate tasks such as calculations for stability, internal power dissipation, current limit; heat sink selec-
tion; Apex’s complete Application Notes library; Technical Seminar Workbook; and Evaluation Kits.
CURRENT LIMIT
For proper operation, the current limit resistor (R_CL) must be connected as shown in the external connection dia-
gram. For optimum reliability the resistor value should be set as high as possible. The value is calculated as follows;
with the maximum practical value of 16 ohms.
R_CL = ^._I⁶_LI _M^{5  }   
40"


%$
5_$

$
SAFE OPERATING AREA (SOA)

The MOSFET output stage of this power operational am-
plifier has two distinct limitations:

1. The current handling capability of the MOSFET ge-
ometry 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

energy flyback, external fast-recovery diodes should be

used.

N4
N4

5
$
5
$


$


$
SAFE OPERATING CURVES

The safe operating area curves define the maximum ad-

ditional internal power dissipation the amplifier can toler-

ate when it produces the necessary output to drive an
external load.
INPUT PROTECTION


        
4611-:
50
065165
%*''&3&/5*"-
7₄
m7₀
7
Although the PA92 can withstand differential voltages up to ±20V, addi-
7₄
tional external protection is recommended. Low leakage, low capacitance
;
JFETs connected as diodes are recommended (e.g. 2N4416, Q1-Q4 in
Figure 2). The differential input voltage will be clamped to ±1.4V. This is
sufficient overdrive to produce maximum power bandwidth.
POWER SUPPLY PROTECTION
Unidirectional zener diode transient suppressors are recommended as
protection on the supply pins. See Figure 2. The zeners clamp transients
m*/
2
2
*/



2

1"
2



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 performance including
'*(63&

07&370-5"(&
1305&$5*0/
;
m7₄
power-on overshoot and power-off polarity reversals as well as line regu-
lation.
Conditions which can cause open circuits or polarity reversals on either power supply rail should be avoided or pro-
tected against. Reversals 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.
PA92U