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CS5210-1

10A LDO 3-Pin Adjustable Linear Regulator

Cherry semiconductor 

Application Notes: continued

Stability Considerations

The output 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 solution.

However, when the circuit operates at low temperatures,

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

ably. The capacitor manufacturerÕs data sheet provides this

information.

A 300µF tantalum capacitor will work for most applica-

tions, but with high current regulators such as the CS5210

the transient response and stability improve with higher

values 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

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 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 CS5210-1 regulator, the discharge path is through a

large junction and protection diodes are not usually need-

ed. If the regulator is used with large values of output

capacitance and the input voltage is instantaneously short-

ed to ground, damage can occur. In this case, a diode con-

nected as shown in Figure 3 is recommended.

A rule of thumb useful in determining if a protection diode

is required is to solve for current

C ´V

I= T , where

I

is the current flow out of the load capacitance

when VIN is shorted,

C

is the value of load capacitance

V

is the output voltage, and

T

is the time duration required for VIN to transition

from high to being shorted.

If the calculated current is greater than or equal to the typi-

cal short circuit current valued provided in the specifica-

tions, serious thought should be given to include a protec-

tion diode.

VIN

VOUT

CS5210-1

Adj

Figure 3:

Current Limit

The internal current limit circuit limits the output current

under excessive load conditions and protects the regulator.

Short Circuit Protection

The device includes foldback short circuit current limit that

clamps the output current at approximately two amperes

less than its current limit value.

Thermal Shutdown

The thermal shutdown circuitry is guaranteed by design to

become activated above a die junction temperature of

150¡C and to shut down the regulator output. This circuit-

ry includes a thermal hysteresis circuit with 25¡C of typical

hysteresis, thereby allowing the regulator to recover from a

thermal fault automatically.

Calculating Power Dissipation and Heat Sink

Requirements

High power regulators such as the CS5210-1 usually oper-

ate at high junction temperatures. Therefore, it is important

to calculate the power dissipation and junction tempera-

tures accurately to ensure that an adequate heat sink is

used. Since the package tab is connected to Vout on the

CS5210-1, electrical isolation may be required for some

applications. Also, as with all high power packages, ther-

mal compound in necessary to ensure proper heat flow.

For added safety, this high current LDO includes an inter-

nal thermal shutdown circuit.

The thermal characteristics of an IC depend on the follow-

ing four factors. Junction temperature, ambient tempera-

ture, die power dissipation, and the thermal resistance

6

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