Philips Semiconductors

Product data

SA57005

Multiple output low noise, low dropout linear regulator

2002 Jun 20

7

TECHNICAL DISCUSSION

As illustrated in the circuit diagram, each of the regulators in the

SA57005 consists of a 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 connected to the output voltage pins.

The reference will be activated if any of the PS1 and PS2/3 switches

is turned on.

The reference is connected to the error amplifier’s non-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 output of the error amplifier goes up,

which pulls down the pass transistor’s gate. This allows more

current to pass to the output and increase the output voltage. On the

other hand, if the feedback voltage is too high the pass transistor

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

resulting a decrease in output voltage.

SL01705

8 GND

2

PS2/3

1

PS1

TERMINAL

PROTECT

4

Figure 10. Functional diagram.