CS5257A−1

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6

0.5

1.5

2.5

3.5

4.5

915.4

916.0

916.1

916.2

916.3

916.4

915.5

915.6

915.7

915.8

915.9

Figure 15. Adjust Pin Current vs Output Current

0

1.0

3.0

2.0

7.0

Output Current (A)

4.0

6.0

5.0

1.0

0.9

0.8

0.7

0.6

0.5

0.4

0.3

0.2

0.1

0

77

76

75

74

73

72

0

1.0

3.0

2.0

8.0

Output Current (A)

4.0

6.0

5.0

7.0

APPLICATIONS NOTES

THEORY OF OPERATION

The CS5257A−1 linear regulator provides adjustable

voltages from 1.25 V to 5.0 V at currents up to 7.0 A. The

regulator is protected against short circuits, and includes a

thermal shutdown 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.

The CS5257A−1 utilizes a two supply approach to

maximize efficiency. The collector of the power device is

power for the control circuitry and the drive for the output

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

typically limited to about 3.0 mA 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 CS5257A−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 CS5257A−1 five terminal linear regulator includes a

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.