MIC5239_07 Datasheet, PDF (9/14 Pages) Micrel Semiconductor – Low Quiescent Current 500mA μCap LDO Regulator

Micrel
Application Information
The MIC5239 provides all of the advantages of the
MIC2950: wide input voltage range, and reversed-
battery protection, with the added advantages of
reduced quiescent current and smaller package.
Additionally, when disabled, quiescent current is reduced
to 0.1µA.
Enable
A low on the enable pin disables the part, forcing the
quiescent current to less than 0.1µA. Thermal shutdown
and the error flag are not functional while the device is
disabled. The maximum enable bias current is 2µA for a
2.0V input. An open-collector pull-up resistor tied to the
input voltage should be set low enough to maintain 2V
on the enable input. Figure 1 shows an open-collector
output driving the enable pin through a 200kΩ pull-up
resistor tied to the input voltage.
In order to avoid output oscillations, slow transitions from
low-to-high should be avoided.
V
5V _200k
200k
MIC5239
IN OUT
EN FLG
GND
V
V
C
Figure 1. Remote Enable
Input Capacitor
An input capacitor may be required when the device is
not near the source power supply or when supplied by a
battery. Small, surface mount ceramic capacitors can be
used for bypassing. Larger values may be required if the
source supply has high ripple.
Output Capacitor
The MIC5239 has been designed to minimize the effect
of the output capacitor ESR on the closed loop stability.
As a result, ceramic or film capacitors can be used at the
output. Figure 2 displays a range of ESR values for a
10µF capacitor. Virtually any 10µF capacitor with an
ESR less than 3.4Ω is sufficient for stability over the
entire input voltage range. Stability can also be
maintained throughout the specified load and line
conditions with 4.7µF film or ceramic capacitors.
MIC5239
Figure 2. Output Capacitor ESR
Error Detection Comparator Output
The FLAG pin is an open-collector output which goes
low when the output voltage drops 5% below it’s
internally programmed level. It senses conditions such
as excessive load (current limit), low input voltage, and
over temperature conditions. Once the part is disabled
via the enable input, the error flag output is not valid.
Overvoltage conditions are not reflected in the error flag
output. The error flag output is also not valid for input
voltages less than 2.3V.
The error output has a low voltage of 400mV at a current
of 200µA. In order to minimize the drain on the source
used for the pull-up, a value of 200kΩ to 1MΩ is
suggested for the error flag pull-up. This will guarantee a
maximum low voltage of 0.4V for a 30V pull-up potential.
An unused error flag can be left unconnected.
4.75V
Output
Voltage
0V
Error FLAG
Output
NOT
VALID
VALID ERROR
NOT
VALID
5V
Input
Voltage 1.3V
0V
Figure 3. Error FLAG Output Timing
Thermal Shutdown
The MIC5239 has integrated thermal protection. This
feature is only for protection purposes. The device
should never be intentionally operated near this
temperature as this may have detrimental effects on the
life of the device. The thermal shutdown may become
inactive while the enable input is transitioning from a
high to a low. When disabling the device via the enable
pin, transition from a high to low quickly. This will insure
that the output remains disabled in the event of a
thermal shutdown.
December 2007
9
M9999-121007