CS5207−1

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APPLICATIONS INFORMATION

The CS5207−1 linear regulator provides adjustable

voltages at currents up to 7.0 A. The regulator is protected

against short circuit, and includes thermal shutdown and

safe area protection (SOA) circuitry. The SOA protection

circuitry decreases the maximum available output current as

the input−output differential voltage increases.

The CS5207−1 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 adjustable regulator has an output voltage range of

1.25 V to 13 V. An external resistor divider sets the output

voltage as shown in Figure 7. 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 μA) 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

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

for best tracking over temperature. The adjust pin is

bypassed to improve the transient response and ripple

rejection of the regulator.

Figure 7. Resistor Divider Scheme

for the Adjustable Version

CS5207−1

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Stability Considerations

The output or compensation capacitor helps determine

three main characteristics of a linear regulator: start−up

delay, load transient response, and loop stability.

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 considerably. The capacitor manufacturer’s data sheet

provides this information.

A 22 μF tantalum capacitor will work for most

applications, but with high current regulators such as the

CS5207−1 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:

DV + DI

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

regulator it is sometimes necessary to add protection diodes.

If the input voltage of the regulator gets shorted, the output

capacitor will discharge into the output of the regulator. The

discharge current depends on the value of the capacitor, the

CS5207−1 linear 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, damage can occur. In this case, a diode connected

as shown in Figure 8 is recommended.

Figure 8. Protection Diode Scheme for Adjustable

Output Regulator

CS5207−1

Adj

IN4002 (Optional)