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Fabricante

CS5203-1

3A Adjustable Linear Regulator

Cherry semiconductor 

Applications Information: continued

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 CS5203-1 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

Output Voltage Sensing

Since the CS5203-1 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 the adjustable regulator, the best load regulation

occurs when R1 is connected directly to the output pin of

the regulator as shown in Figure 4. If R1 is connected to the

load, RC is multiplied by the divider ratio and the effective

resistance between the regulator and the load becomes

( ) RC ´ R1 + R2

R1

RC = conductor parasitic resistance

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.

Protection Diodes

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 CS5203-1 linear regulator, the discharge path is

through a large junction and protection diodes are not usu-

ally needed. If the regulator is used with large values of

output capacitance and the input voltage is instantaneous-

ly shorted to ground, damage can occur. In this case, a

diode connected as shown in Figure 3 is recommended.

VIN

C1

IN4002 (optional)

VIN

VOUT

CS-5203-1

R1

Adj

VOUT

C2

R2

CAdj

Figure 3. Protection diode scheme for large output capacitors.

VIN

VIN

VOUT

conductor parasitic

RC resistance

CS5203-1

R1

Adj

RLOAD

R2

Figure 4. Grounding scheme for the adjustable output regulator to min-

imize parasitic resistance effects.

Calculating Power Dissipation and Heat Sink Requirements

The CS5203-1 linear regulator includes thermal shutdown

and current limit circuitry to protect the device. High

power regulators such as these usually operate at high

junction temperatures so it is important to calculate the

power dissipation and junction temperatures accurately to

ensure that an adequate heat sink is used.

The case is connected to VOUT on the CS5203-1 , and elec-

trical isolation may be required for some applications.

Thermal compound should always be used with high cur-

rent regulators such as these.

The thermal characteristics of an IC depend on the follow-

ing four factors:

1. Maximum Ambient Temperature TA (¡C)

2. Power dissipation PD (Watts)

3. Maximum junction temperature TJ (¡C)

4. Thermal resistance junction to ambient RQJA (C/W)

These four are related by the equation

6

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