CS5203−1

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5

APPLICATIONS INFORMATION

The CS5203−1 linear regulator provides adjustable voltages

at currents up to 3.0 A. The regulator is protected against

overcurrent conditions and includes thermal shutdown.

The CS5203−1 has a composite PNP−NPN output

transistor and requires an output capacitor for stability. A

detailed procedure for selecting this capacitor is included in

the Stability Considerations section.

Adjustable Operation

The CS5203−1 has an output voltage range of 1.25 V to

5.5 V. An external resistor divider sets the output voltage as

shown in Figure 12. The regulator maintains a fixed 1.25V

(typical) reference between the output pin and the adjust pin.

A resistor divider network R1 and R2 causes a fixed current

to flow to ground. This current creates a voltage across R2

that adds to the 1.25 V across R1 and sets the overall output

voltage. The adjust pin current (typically 50

mA) also flows

through R2 and adds a small error that should be taken into

The output voltage is set according to the formula:

VOUT + VREF

R1 ) R2

R1

) IAdj

R2

pin current.

R1 is chosen so that the minimum load current is at least

2.0 mA. R1 and R2 should be the same type, e.g. metal film

for best tracking over temperature. While not required, a

bypass capacitor from the adjust pin to ground will improve

ripple rejection and transient response. A 0.1

mF tantalum

capacitor is recommended for “first cut” design. Type and

value may be varied to obtain optimum performance vs.

price.

Figure 12. Resistor Divider Scheme

CS5203−1

Adj

The CS5201−1 linear regulator has an absolute maximum

in excess of 7.0 V. The main considerations in such a design

are power−up and short circuit capability.

is fairly slow, typically on the order of several tens of

milliseconds, while the regulator responds in less than one

microsecond. In this case, the linear regulator begins

large enough that the pass transistor conducts current. The

load at this point is essentially at ground, and the supply

voltage is on the order of several hundred millivolts, with the

result that the pass transistor is in dropout. As the supply to

which the IC is in regulation. Further increase in the supply

voltage brings the pass transistor out of dropout. The result

is that the output voltage follows the power supply ramp−up,

staying in dropout until the regulation point is reached. In

this manner, any output voltage may be regulated. There is

no theoretical limit to the regulated voltage as long as the

However, the possibility of destroying the IC in a short

circuit condition is very real for this type of design. Short

circuit conditions will result in the immediate operation of

the pass transistor outside of its safe operating area.

Over−voltage stresses will then cause destruction of the pass

transistor before overcurrent or thermal shutdown circuitry

can become active. Additional circuitry may be required to

fail−safe operation is required. One possible clamp circuit is

illustrated in Figure 13; however, the design of clamp

circuitry must be done on an application by application

basis. Care must be taken to ensure the clamp actually

protects the design. Components used in the clamp design

must be able to withstand the short circuit condition

indefinitely while protecting the IC.

Figure 13. Short Circuit Protection Circuit for

High Voltage Application.

EXTERNAL SUPPLY