CS5203-3GDPR3 datasheet(4/6 Pages) CHERRY

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Applications Information

The CS5203-3 linear regulator provides a fixed 3.3V out-

put voltage at currents up to 3A. The regulator is protect-

ed against overcurrent conditions and includes thermal

shutdown.

The CS5203-3 has a composite PNP-NPN output transistor

and requires an output capacitor for stability.

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 are based on cost, availabili-

ty, size and temperature constraints. A tantalum or alu-

minum 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 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 CS5203-3 the

transient response and stability improve with higher val-

ues of capacitance. The majority of applications for this

regulator involve large changes in load current so the out-

put 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 net-

work 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 CS5203-3 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 instanta-

neously 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 large output capacitors.

Since the CS5203-3 is a three terminal regulator, it is not

possible to provide true remote load sensing. Load regula-

tion is limited by the resistance of the conductors connect-

ing the regulator to the load. For best results, the regulator

should be connected as shown in figure 2.

Output Voltage Sensing

VOUT

VIN

CS5203-3

VIN

GND

VOUT

IN4002

(optional)

Protection Diodes

Stability Considerations

+200

-200

Time (

ms)

DVOUT

(mV)

I(A)

VIN = 5V

VOUT = 3.3V

CIN = 100mF

COUT = 10mF Tantalum

Transient Response

Typical Performance Characteristics: continued

6.00

5.00

4.00

3.00

2.00

1.00

0.00

1.0

1.50

2.0

2.5

3.0

3.5

VIN-VOUT (V)

Short Circuit Current vs. VIN - VOUT

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