CS5253-1GDPR5 datasheet(6/9 Pages) CHERRY

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Typical Performance Characteristics: Continued

100

120

140

Junction Temperature (C)

VPOWER = 6V

VOUT = 0V

VCONTROL not connected

VPOWER Only Output Current vs Junction Temperature

The CS5253-1 linear regulator provides adjustable voltages

from 1.26V to 5V at currents up to 3A. 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 CS5253-1 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 for the con-

trol 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 voltage will

not turn on until both supplies are operating. If the control

voltage comes up first, the output current will be limited to

about three milliamperes 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 voltage

comes up. The output can never come up unregulated.

The CS5253-1 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 CS5253-1 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.

Adjustable Operation

This LDO adjustable regulator has an output voltage range

of 1.26V 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 1.260V reference

between the output pin and the adjust pin.

A resistor divider network R1 and R2 causes a fixed current

to flow to ground. This current creates a voltage across R2

that adds to the 1.260V across R1 and sets the overall out-

put 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 neces-

sary. The output voltage is set according to the formula:

VOUT = 1.260V ´

+ 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 at least 10mA. R1 and R2 should be of the same composi-

tion for best tracking over temperature. The divider resis-

tors should be placed physically as close to the load as pos-

sible.

Figure 1: Typical application schematic. The resistor divider sets VOUT,

with the internal 1.260V reference dropped across R1.

SENSE

OUT

CONTROL

POWER

CS5253-1

Adjust

3.3V

2.5V

@3A

R1+R2

Design Guidelines

Theory of Operation

100

120

140

Junction Temperature (C)

IOUT = 3A

IOUT = 1A

IOUT = 100mA

VPOWER = 2.05V

VCONTROL = 2.75V

VCONTROL Supply Current vs Junction Temperature

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