MIC49500 datasheet(9/11 Pages) MICREL

9 / 11 page

Micrel, Inc.

MIC49500

November 2005

M9999-110805

(408) 955-1690

The heat sink may be significantly reduced in

applications where the maximum input voltage is

known and large compared with the dropout voltage.

Use a series input resistor to drop excessive voltage

and distribute the heat between this resistor and the

regulator. The low dropout properties of the MIC49500

allow significant reductions in regulator power

dissipation and the associated heat sink without

compromising performance. When this technique is

employed, a capacitor of at least 1µF is needed

directly between the input and regulator ground. Refer

to Application Note 9 for further details and examples

on thermal design and heat sink specification.

Minimum Load Current

The MIC49500, unlike most other high current

regulators, does not require a minimum load to

maintain output voltage regulation.

Power Sequencing

There is no power sequencing requirement for VIN and

VBIAS, giving more flexibility to the user.

Adjustable Regulator Design

The

MIC49500

adjustable

version

allows

programming the output voltage anywhere between

0.7Vand 6V. Two resistors are used. The resistor

value between VOUT and the adjust pin should not

exceed 10kΩ. Larger values can cause instability. The

resistor values are calculated by:

R1 = R2 ×

VOUT

0.7

± 1

Where VOUT is the desired output voltage.

Enable

The fixed output voltage versions of the MIC49500

feature an active high enable input (EN) that allows

on-off control of the regulator. Current drain reduces

to “zero” when the device is shutdown, with only

microamperes of leakage current. The EN input has

TTL/CMOS compatible thresholds for simple logic

interfacing. EN may be directly tied to VIN and pulled

up to the maximum supply voltage.

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