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CS5258-1

8A LDO 5-Pin Adjustable Linear Regulator

Cherry semiconductor 

Typical Performance Characteristics: continued

Minimum Load Current vs VPOWER-VOUT

916.400

916.300

916.200

916.100

916.000

915.900

915.800

915.700

915.600

915.500

915.400

0.50

VCONTROL = 5V

D VOUT = +1%

1.50

2.50

VPOWER-VOUT (V)

3.50

4.50

Application Notes

Theory of Operation

The CS5258-1 linear regulator provides adjustable voltages

from 1.25V to 5V at currents up to 8A. The regulator is pro-

tected against short circuits, and includes a thermal shut-

down circuit with hysteresis. The output, which is current

limited, consists of a PNP-NPN transistor pair and requires

an output capacitor for stability. A detailed procedure for

selecting this capacitor is included in the Stability

Considerations section.

VPOWER Function

The CS5258-1 utilizes a two supply approach to maximize

efficiency. The collector of the power device is brought out

to the VPOWER pin to minimize internal power dissipation

under high current loads. VCONTROL provides power for

the control circuitry and the drive for the output NPN

transistor. VCONTROL should be at least 1V greater than the

output voltage. Special care has been taken to ensure that

there are no supply sequencing problems. The output volt-

age will not turn on until both supplies are operating. If

the control voltage comes up first, the output current will

be typically limited to about 3mA until the power input

voltage comes up. If the power input voltage comes up

first the output will not turn on at all until the control volt-

age comes up. The output can never come up unregulated.

The CS5258-1 can also be used as a single supply device

with the control and power inputs tied together. In this

mode, the dropout will be determined by the minimum

control voltage.

Output Voltage Sensing

The CS5258-1 five terminal linear regulator includes a ded-

icated VSENSE function. This allows for true Kelvin sensing

of the output voltage. This feature can virtually eliminate

errors in the output voltage due to load regulation.

Regulation will be optimized at the point where the sense

pin is tied to the output.

Design Guidelines

Adjustable Operation

This LDO adjustable regulator has an output voltage range

of 1.25V to 5V. An external resistor divider sets the output

voltage as shown in Figure 1. The regulatorÕs voltage sens-

ing error amplifier maintains a fixed 1.253V reference

between the output pin and the adjust pin.

A resistor divider network R1 and R2 causes a fixed cur-

rent to flow to ground. This current creates a voltage

across R2 that adds to the 1.253V across R1 and sets the

overall output voltage. The adjust pin current (typically

50µA) also flows through R2 and adds a small error that

should be taken into account if precise adjustment of VOUT

is necessary. The output voltage is set according to the

formula:

( VOUT = 1.253V ´

) R1+R2

R1

+ R2 ´ IADJ

The term IADJ ´ R2 represents the error added by the adjust

pin current.

R1 is chosen so that the minimum load current is a least

10mA. R1 and R2 should be of the same composition for

best tracking over temperature. The divider resistors

should be located as close to the load as possible.

VCONTROL VOUT

CS5258-1

VPOWER VSENSE

Adjust

R1

R2

Figure 1: An external resistor divider sets the value of VOUT. The 1.253V

reference voltage drops across R1.

6

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