PA51 Datasheet, PDF (4/4 Pages) Cirrus Logic – POWER OPERATIONAL AMPLIFIERS

OPERATING
CONSIDERATIONS
PA51 • PA51A
GENERAL
Please read Application Note 1 "General Operating Con-
siderations" 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, in-
ternal power dissipation, current limit and heat sink selection.
The "Application Notes" and "Technical Seminar" sections
contain a wealth of information on specific types of applications.
Package outlines, heat sinks, mounting hardware and other
accessories are located in the "Packages and Accessories"
section. Evaluation Kits are available for most Apex product
models, consult the "Evaluation Kit" section for details. For
the most current version of all Apex product data sheets, visit
www.apexmicrotech.com.
SAFE OPERATING AREA (SOA)
The output stage of most power amplifiers has three distinct
limitations:
1. The current handling capability of the transistor geometry
and the wire bonds.
2. The second breakdown effect which occurs whenever the
simultaneous collector current and collector-emitter voltage
exceeds specified limits.
3. The junction temperature of the output transistors.
���
��
���
���
���
�������
�
�
���_{�������������}
���
�
�
��������
���
���
���
���
���
���
�
�
��
�� ��
�� �� �� �� ��
���������������������������������������_�����_�����
The SOA curves combine the effect of of all limits for this
Power Op Amp. For a given application, the direction and
magnitude of the output current should be calculated or mea-
sured and checked against the SOA curves. This is simple
for resistive loads but more complex for reactive and EMF
generating loads. The following guidelines may save extensive
analytical efforts.
1. Under transient conditions, capacitive and dynamic* induc-
tive loads up to the following maximums are safe:
CAPACITIVE LOAD
INDUCTIVE LOAD
±V_S
I_LIM = 5A
I_LIM = 10A
I_LIM = 5A I_LIM = 10A
40V
400µF
200µF
11mH
4.3mH
35V
800µF
400µF
20mH
5.0mH
30V
1,600µF
800µF
35mH
6.2mH
25V
5.0mF
2.5mF
50mH
15mH
20V
10mF
5.0mF
400mH 20mH
15V
20mF
10mF
**
100mH
* If the inductive load is driven near steady state conditions,
allowing the output voltage to drop more than 8V below the
supply rail with I_LIM = 10A or 15V below the supply rail with
I_LIM = 5A while the amplifier is current limiting, the inductor
should be capacitively coupled or the current limit must be
lowered to meet SOA criteria.
** Second breakdown effect imposes no limitation but thermal
limitations must still be observed.
2. The amplifier can handle any EMF generating or reactive
load and short circuits to the supply rail or shorts to common
if the current limits are set as follows at T_C = 85°C.
SHORT TO ±V_S
SHORT TO
±V_S
C, L, OR EMF LOAD
COMMON
45V
0.1A
1.3A
40V
0.2A
1.5A
35V
0.3A
1.6A
30V
0.5A
2.0A
25V
1.2A
2.4A
20V
1.5A
3.0A
15V
2.0A
4.0A
These simplified limits may be exceeded with further analysis
using the operating conditions for a specific application.
3.The output stage is protected against transient flyback. How-
ever, for protection against sustained, high energy flyback,
external fast-recovery diodes should be used.
CURRENT LIMIT
Proper operation requires the use of two current limit resis-
tors, connected as shown in the external connection diagram.
The minimum value for R_CL is .06 ohm, however for optimum
reliability it should be set as high as possible. Refer to the
“General Operating Considerations” section of the handbook
for current limit adjust details.
A^ThPⁱE^s X^datM^a I^shC^eR^eO^t T^haE^sC^bH^eN^enO^cL^aO^reG^fuY^llyC^cO^heR^cP^keO^dR^aA^ndTI^isO^bN^eli•^eve5^d9^t8^o 0^be N^reO^liaR^bT^leH^{, h}S^owH^eA^veN^r,NⁿO^oN^resR^poOⁿA^siD^bili•^ty T^isU^aC^ssS^uO^mN^ed, ^fA^orR^pI^oZ^sO^sibN^leAⁱⁿ8^ac5^c7^ur4^ac1^ies•^orU^oS^mA^iss•^ionA^s.P^AP^llL^sI^pC^eA^ciT^fiI^cO^atN^ioS^nsH^arO^eT^sL^ubI^jN^ecE^t:^to1^ch(^a8ⁿ0^ge0^w)^it5^ho4^u6^t -ⁿ2^ot7^ic3^e9^.
4
PA51U REV N MARCH 2005 © 2005 Apex Microtechnology Corp.