August 2005

7

MIC5156/5157/5158

MIC5156/5157/5158

Micrel, Inc.

Functional Description

A Super LDO Regulator is a complete regulator built around

Micrel’s Super LDO Regulator Controller.

Refer to Block Diagrams MIC5156, MIC5157, and

MIC5158.

Version Differences

The MIC5156 requires an external voltage for MOSFET gate

drive and is available in 3.3V fixed output, 5V fixed output, or

adjustable output versions. With 8-pins, the MIC5156 is the

smallest of the Super LDO Regulator Controllers.

The MIC5157 and MIC5158 each have an internal charge

pump which provides MOSFET gate drive voltage. The

MIC5157 has a selectable fixed output of 3.3V, 5V, or 12V.

The MIC5158 may be configured for a fixed 5V or adjustable

output.

Enable (EN)

the controller in shutdown mode. A TTL high on EN enables

the internal bias circuit which powers all internal circuitry. EN

must be pulled high if unused. The voltage applied to EN may

be as high as 36V.

The controller draws less than 1µA in shutdown mode.

Gate Enhancement

The Super LDO Regulator Controller manages the gate-

1.235V

Bandgap

Reference

Clamp

Internal

Bias

Error

Amp

75mV

35mV

EA

S (Source)

Comparator

D (Drain)

G (Gate)

Comparator

to all

internal blocks

GND

Regulated

+3.6V Output

+5V Input

Q1

IRFZ44

3mΩ

1µF

16.6V

32k

10k

5V

FB

Oscillator

Charge Pump

Tripler

C1+ C1– C2+ C2–

0.1µF

0.1µF

C1

C2

C3

FLAG

19.1k

10.0k

EN

Enable

Shutdown

Block Diagram MIC5158

Block Diagram with External Components

Adjustable Power Supply, 3.6V Configuration

to-source enhancement voltage for an external N-channel

MOSFET(regulatorpasselement)placedbetweenthesupply

and the load. The gate-to-source voltage may vary from 1V

to 16V depending upon the supply and load conditions.

Because the source voltage (output) approaches the drain

voltage (input) when the regulator is in dropout and the

MOSFET is fully enhanced, an additional higher supply

voltage is required to produce the necessary gate-to-source

enhancement. This higher gate drive voltage is provided by

an external gate drive supply (MIC5156) or by an internal

charge pump (MIC5157 and MIC5158).

Gate Drive Supply Voltage (MIC5156 only)

The gate drive supply voltage must not be more than 14V

necessary gate drive supply voltage is:

where:

MOSFET gate enhancement

The error amplifier uses the gate drive supply voltage to drive

the gate of the external MOSFET. The error amplifier output