PA05 datasheet(4/4 Pages) APEX

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APEX MICROTECHNOLOGY CORPORATION • 5980 NORTH SHANNON ROAD • TUCSON, ARIZONA 85741 • USA • APPLICATIONS HOTLINE: 1 (800) 546-2739

OPERATING

CONSIDERATIONS

PA05 • PA05A

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,

internal power dissipation, current limit; heat sink selection;

Apex’s complete Application Notes library; Technical Seminar

Workbook; and Evaluation Kits.

CURRENT LIMIT

The two current limit sense lines are to be connected directly

across the current limit sense resistor. For the current limit to

work correctly, pin 11 must be connected to the amplifier out-

put side and pin 10 connected to the load side of the current

limit resistor, R

CL, as shown in Figure 1. This connection will

bypass any parasitic resistances, R

P formed by sockets and

solder joints as well as internal ampliﬁer losses. The current

limiting resistor may not be placed anywhere in the output

circuit except where shown in Figure 1. If current limiting is

not used, pins 10 and 11 must be tied to pin 7.

The value of the current limit resistor can be calculated as

follows:

SAFE OPERATING AREA (SOA)

The MOSFET output stage of this power operational ampli-

ﬁer has two distinct limitations:

1. The current handling capability of the MOSFET geometry

and the wire bonds.

2. The junction temperature of the output MOSFETs.

NOTE: The output stage is protected against transient ﬂy-

back. However, for protection against sustained, high energy

ﬂyback, external fast-recovery diodes should be used.

The output stage thermal protection circuit engages when

junction temperatures reach approximately 175C. If the con-

dition remains that caused the shutdown, the ampliﬁer may

oscillate in and out of shutdown, creating high peak power

stresses reducing the reliability of the device.

SHUTDOWN OPERATION

To disable the output stage, pin 12 is connected to ground

via relay contacts or via an electronic switch. The switching

device must be capable of sinking 2mA to complete shutdown

and capable of standing off the supply voltage +V

S. See Figure

2 for suggested circuits.

From an internal circuitry standpoint, shutdown is just a

special case of current limit where the allowed output current

is zero. As with current limit, however, a small current does

ﬂow in the output during shutdown. A load impedance of 100

ohms or less is required to insure the output transistors are

turned off. Note that even though the output transistors are off

the output pin is not open circuited because of the shutdown

operating current.

BOOST OPERATION

With the V

BOOST feature, the small signal stages of the ampli-

ﬁer are operated at higher supply voltages than the ampliﬁer’s

high current output stage. +V

BOOST (pin 9), and –VBOOST

(pin

5) are connected to the small signal circuitry of the ampliﬁer.

S (pin 8) and –VS (pin 6) are connected to the high current

output stage. An additional 5V on the V

BOOST pins is sufﬁcient

to allow the small signal stages to drive the output transistors

into saturation and improve the output voltage swing for extra

efﬁcient operation when required. When close swings to the

supply rails is not required the +V

BOOST and +VS pins must be

strapped together as well as the –V

BOOST and –VS pins. The

boost voltage pins must not be at a voltage lower than the

S pins.

COMPENSATION

The external compensation components C

C and RC are con-

nected to pins 3 and 4. Unity gain stability can be achieved at

any compensation capacitance greater than 470 pF with at

least 60 degrees of phase margin. At higher gains, more phase

shift can be tolerated in most designs and the compensation

capacitance can accordingly be reduced, resulting in higher

bandwidth and slew rate. Use the typical operating curves as

a guide to select C

C and RC for the application.

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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.

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