Philips Semiconductors

Product data

SA57031-XX

Micropower 150 mA, low-noise, low dropout linear

regulator with on/off

2003 Jun 23

8

TECHNICAL DISCUSSION

As illustrated in Figure 16, the SA57031 consists of a band-gap

voltage reference, an error amplifier, P-channel pass transistor,

current limit circuit and an internal feedback voltage divider. The

output voltage is fed back through an internal resistor voltage divider

The reference is connected to the error amplifier’s inverting input.

The error amplifier compares the reference with the feedback

voltage and amplifies the difference. If the feedback voltage is lower

than the reference voltage, the pass transistor’s gate is pulled lower,

which allows more current to pass to the output and increase the

output voltage. If the feedback voltage is too high, the pass

transistor gate is pulled up, allowing less current to pass to the

output, resulting in a decrease in output voltage.

SA00634

2

4

1

3

SA57031-XX

GND

ON/OFF

CURRENT

LIMITER

Figure 16. Block diagram (bottom view).