MIC2212 Datasheet, PDF (9/10 Pages) Micrel Semiconductor – Dual uCap LDO and Power-On Reset

MIC2212
Functional Diagram
VIN
LDO1
EN1
EN2
SET
CBYP
Reference
OUT1
LDO2
POR & Delay
OUT2
POR
GND
MIC2212 Fixed Voltage Block Diagram
Micrel
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 1µA 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 1µF 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 0.01µF, but it can be increased without
limit.
Output Capacitor
Each regulator output requires a 1µF ceramic output capaci-
tor for stability. The output capacitor value can be increased
to improve transient response, but performance has been
optimized for a 1µF 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.
August 2004
9
M9999-080504