CS5207-2 datasheet(3/5 Pages) CHERRY

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Load Regulation vs. Output Current

Ripple Rejection vs Frequency

Typical Performance Characteristics: continued

the CS5207-2 linear regulator provides a fixed 1.5V out-

put at currents up to 7A. 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 CS5207-2 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.

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 capaci-

tor with almost zero ESR can cause instability. The alu-

minum electrolytic capacitor is the least expensive solu-

tion. However, when the circuit operates at low tempera-

tures, both the value and ESR of the capacitor will vary

considerably. The capacitor manufacturersÕ data sheet pro-

vides this information.

A 22µF tantalum capacitor will work for most applications,

but with high current regulators such as the CS5207-2 the

transient response and stability improve with higher val-

ues of capacitor. The majority of applications for this regu-

lator 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

load transient conditions. The output capacitor network

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

When large external capacitors are used with a linear regu-

lator 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 capaci-

tor, the output voltage and the rate at which VIN drops. In

the CS5207-2, the discharge path is through a large junc-

tion 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 1 is recommended.

Figure 1. Protection diode scheme for fixed output regulators.

VOUT

VIN

CS5207-2

VIN

Gnd

VOUT

IN4002

(optional)

Protection Diodes

Stability Considerations

Applications Information

0.025

0.000

0.050

0.075

0.100

0.200

Output Current (A)

TCASE = 0°C

0.125

0.150

0.175

TCASE = 125°C

TCASE = 25°C

0.0

101

Frequency (Hz)

10.0

20.0

30.0

40.0

50.0

60.0

70.0

80.0

90.0

100.0

102

103

104

105

TCASE = 25°C

IOUT = 7A

(VIN Ð VOUT) = 3V

VRIPPLE = 1.6VPP

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