CS5210−1

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APPLICATION NOTES

THEORY OF OPERATION

The CS5210−1 linear regulator has a composite

PNP−NPN output stage that requires an output capacitor for

stability. A detailed procedure for selecting this capacitor is

included in the Stability Considerations section.

ADJUSTABLE OPERATION

Design Guidelines

This LDO adjustable regulator has an output voltage

range of 1.25 V to 4.5 V. An external resistor divider sets the

output voltage as shown in Figure 11. The regulator’s

voltage sensing error amplifier maintains a fixed 1.25 V

reference between the output pin and the adjust pin.

voltage. The adjust pin current (typically 50 μA) also flows

output voltage is set according to the formula:

VOUT + VREF

R1 ) R2

R1

) R2

IAdj

pin current.

tracking over temperature. The divider resistors should be

placed as close to the IC as possible and connected to the

output with a seperate metal trace.

Figure 11.

CS5210−1

Adj

While not required, a bypass capacitor connected between

the adjust pin and ground will improve transient response

and ripple rejection. A 0.1 μF tantalum capacitor is

recommended for “first cut” design. Value and type may be

varied to optimize performance vs price.

The CS5210−1 linear regulator has an absolute maximum

in excess of 6.0 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

differential is large enough that the pass transistor conducts

order of several hundred millivolts, so the pass transistor is

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

6.0 V is not exceeded.

However, the maximum ratings of the IC will be exceeded

in a short circuit condition. 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

to less than 6.0 V if failsafe operation is required. One

possible clamp circuit is illustrated in Figure 12; 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 conditions

indefinitely while protecting the IC.

Figure 12.

EXTERNAL SUPPLY