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CS52510-1

10A LDO 5-Pin Adjustable Linear Regulator

Cherry semiconductor 

Application Notes: continued

While not required, a bypass capacitor connected between

the adjust pin and ground will improve transient response

and ripple rejection. A 0.1µF tantalum capacitor is recom-

mended for Òfirst cutÓ design. Value and type may be varied

to optimize performance vs. price.

Other Adjustable Operation Considerations

The CS52510-1 linear regulator has an absolute maximum

specification of 6V for the voltage difference between VIN

and VOUT. However, the IC may be used to regulate voltages

in excess of 6V. The two main considerations in such a

design are the sequencing of power supplies and short cir-

cuit capability.

Power supply sequencing should be such that the VCONTROL

supply is brought up coincidentally with or before the VPOW-

ER supply. This allows the IC to begin charging output capac-

itor as soon as the VPOWER to VOUT differential is large

enough that the pass transistor conducts. As VPOWER increas-

es, the pass transistor will remain in dropout, and current is

passed to the load until VOUT is in regulation. Further

increase in the supply voltage brings the pass transistor out

of dropout. In this manner, any output voltage less than 13V

may be regulated, provided the VPOWER to VOUT differential

is less than 6V. In the case where VCONTROL and VPOWER are

shorted, there is no theoretical limit to the regulated voltage

as long as the VPOWER to VOUT differential of 6V is not

exceeded.

There is a possibility of damaging the IC when VPOWER-VIN

is greater than 6V if a short circuit occurs. Short circuit condi-

tions will result in the immediate operation of the pass tran-

sistor outside of its safe operating area. Over-voltage stresses

will then cause destruction of the pass transistor before over-

current or thermal shutdown circuitry can become active.

Additional circuitry may be required to clamp the VPOWER to

VOUT differential to less than 6V if fail safe operation is

required. One possible clamp circuit is illustrated in Figure 2;

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.

External Supply

The capacitor value and type is based on cost, availability,

size and temperature constraints. A tantalum or aluminum

electrolytic capacitor is best, since a film or ceramic capacitor

with almost zero ESR can cause instability. The aluminum

electrolytic capacitor is the least expensive solution.

However, when the circuit operates at low temperatures,

both the value and ESR of the capacitor will vary consider-

ably. The capacitor manufacturers data sheet provides this

information.

A 300µF tantalum capacitor will work for most applications,

but with high current regulators such as the CS52510-1 the

transient response and stability improve with higher values

of capacitor. The majority of applications for this regulator

involve large changes in load current so the output capacitor

must supply the instantaneous load current. The ESR of the

output capacitor causes an immediate drop in output voltage

given by:

ÆV = ÆI ´ ESR.

For microprocessor applications it is customary to use an

output capacitor network consisting of several tantalum and

ceramic capacitors in parallel. This reduces the overall ESR

and reduces the instantaneous output voltage drop under

transient load conditions. The output capacitor network

should be as close to the load as possible for the best results.

Protection Diodes

When large external capacitors are used with a linear regula-

tor it is sometimes necessary to add protection diodes. If the

input voltage of the regulator gets shorted, the output capac-

itor will discharge into the output of the regulator. The dis-

charge current depends on the value of the capacitor, the

output voltage, and the rate at which VCONTROL drops. In the

CS52510-1 regulator, the discharge path is through a large

junction and protection diodes are not usually needed. If the

regulator is used with large values of output capacitance and

the input voltage is instantaneously shorted to ground, dam-

age can occur. In this case, a diode connected as shown in

Figure 3 is recommended. Use of this diode has the added

benefit of bleeding VOUT to ground if VCONTROL is shorted.

This prevents an unregulated output from causing system

damage.

VControl

VSENSE

VPower

VAdjust

VOUT

VCONTROL VOUT

CS52510-1

VPOWER VSENSE

Adjust

Figure 2: Example clamp circuitry for VPOWER - VOUT > 6V.

Figure 3: Diode protection against VCONTROL short circuit conditions.

Stability Considerations

The output compensation capacitor helps determine three

main characteristics of a linear regulator: start-up delay, load

transient response, and loop stability.

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