MIC5239 Datasheet, PDF (8/12 Pages) Micrel Semiconductor – Low Quiescent Current 500mA UCap LDO Regulator

MIC5239
Application Information
The MIC5239 provides all of the advantages of the MIC2950:
wide input voltage range, load dump (positive transients up to
60V), and reversed-battery protection, with the added advan-
tages 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 quies-
cent 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 200k pull-up resistor tied to the input voltage.
In order to avoid output oscillations, slow transitions from low
to high should be avoided.
V_IN
5V _200k
SHUTDOWN
ENABLE
200k
MIC5239
IN OUT
EN FLG
GND
V_ERR
V_OUT
C_OUT
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.
5
4
3
Stable Region
2
1 T_J = 25°C
V_OUT = 10µF
0
5 10 15 20 25 30
INPUT VOLTAGE (V)
Figure 2. Output Capacitor ESR
Micrel
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 pro-
grammed level. It senses conditions such as excessive load
(current limit), low input voltage, and over temperature con-
ditions. 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 200k 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 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.
Current Limit
Figure 4 displays a method for reducing the steady state
short circuit current. The duration that the supply delivers
current is set by the time required for the error flag output to
discharge the 4.7µF capacitor tied to the enable pin. The off
time is set by the 200K resistor as it recharges the 4.7µF
capacitor, enabling the regulator. This circuit reduces the
short circuit current from 800mA to 40mA while allowing for
regulator restart once the short is removed.
1N4148
V_IN
5V _200k
SHUTDOWN
ENABLE
200k
MIC5239
IN OUT
EN FLG
GND
4.7µF
V_ERR
V_OUT
C_OUT
Figure 4. Remote Enable with Short-Circuit
Current Foldback
MIC5239
8
January 2002