August 2004

9

M9999-080504

MIC2212

Micrel

Functional Diagram

OUT1

OUT2

POR

GND

CBYP

SET

EN1

EN2

VIN

LDO1

LDO2

Reference

POR & Delay

MIC2212 Fixed Voltage Block Diagram

Functional Description

The MIC2212 is a high performance, low quiescent current

power management IC consisting of two

µCap low dropout

regulators, a power-on reset (POR) circuit and an open-drain

driver. 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. The second regulator has a POR circuit that

monitors its output voltage and indicates when the output

voltage is within 5% of nominal. The POR offers a delay time

that is externally programmable with a single capacitor to

ground.

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.

Power-On Reset (POR)

The power-on reset output is an open-drain N-Channel

device, requiring a pull-up resistor to either the input voltage

or output voltage for proper voltage levels. The POR output

has a delay time that is programmable with a capacitor from

the SET pin to ground. The delay time can be programmed to

be as long as 1 second.

The SET pin is a current source output that charges a

capacitor that sets the delay time for the power-on reset

output. The current source is a 1

µA current source that

charges a capacitor up from 0V. When the capacitor reaches

1.25V, the output of the POR is allowed to go high.

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 MIC2212 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 a

X7R ceramic capacitor to ensure the same minimum capaci-

tance over the equivalent operating temperature range.