MIC2211

Micrel

M9999-090204

8

August 2004

Functional Diagram

OUT1

OUT2

GND

EN2

CBYP

EN1

VIN

LDO1

LDO2

Reference

MIC2211 Fixed Voltage Block Diagram

Functional Description

The MIC2211 is a high performance, low quiescent current

power management IC consisting of two

µCap low dropout

regulators. The first regulator is capable of sourcing 150mA

at output voltages from 1.25V to 5V. The second regulator is

capable of sourcing 300mA of current at output voltages from

1.25V to 5V.

Enable 1 and 2

The enable inputs allow for logic control of both output

voltages with individual enable inputs. The enable input is

active high, requiring 1.8V for guaranteed operation. The

enable input is CMOS logic and cannot by left floating.

Input Capacitor

Good bypassing is recommended from input to ground to

help improve AC performance. A 1

µF capacitor or greater

located close to the IC is recommended.

Bypass Capacitor

The internal reference voltage of the MIC2211 can be by-

passed with a capacitor to ground to reduce output noise and

increase power supply rejection (PSRR). A quick-start fea-

ture allows for quick turn-on of the output voltage regardless

of the size of the capacitor. The recommended nominal

bypass capacitor is 0.01

µF, but it can be increased without

limit.

Output Capacitor

Each regulator output requires a 1

µF ceramic output capaci-

tor for stability. The output capacitor value can be increased

to improve transient response, but performance has been

optimized for a 1

µF ceramic type output capacitor.

X7R/X5R dielectric-type ceramic capacitors are recom-

mended because of their temperature performance. X7R-

type capacitors change capacitance by 15% over their oper-

ating temperature range and are the most stable type of

ceramic capacitors. Z5U and Y5V dielectric capacitors change

value by as much as 50% and 60% respectively over their

operating temperature ranges. To use a ceramic chip capaci-

tor with Y5V dielectric, the value must be much higher than an

X7R ceramic capacitor to ensure the same minimum capaci-

tance over the equivalent operating temperature range.