MIC2212_06 Datasheet, PDF (9/10 Pages) Micrel Semiconductor – Dual μCap LDO and Power-On Reset

MIC2212
Functional Diagram
VIN
LDO1
EN1
EN2
SET
CBYP
Reference
OUT1
LDO2
POR & Del ay
OUT2
POR
GND
MIC2212 Fixed Voltage Block Diagram
Micrel, Inc.
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
bypassed with a capacitor to ground to reduce output noise
and increase power supply rejection (PSRR). A quick-
start feature 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 operating
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 operat-
ing temperature ranges. To use a ceramic chip capacitor with
Y5V dielectric, the value must be much higher than a X7R
ceramic capacitor to ensure the same minimum capacitance
over the equivalent operating temperature range.
February 2006
9
M9999-022106