MIC5236 Micrel Semiconductor, MIC5236 Datasheet - Page 9

• Manufacturer Part Number: MIC5236
• Description: Low Quiescent Current Cap LDO Regulator Preliminary Information
• Manufacturer: Micrel Semiconductor

Application Information
The MIC5236 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
0.1 A.
Enable
A low on the enable pin disables the part, forcing the quies-
cent current to less than 0.1 A. Thermal shutdown and the
error flag are not functional while the device is disabled. The
maximum enable bias current is 2 A 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.
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 MIC5236 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 10 F capacitor. Virtually
any 10 F capacitor with an ESR less than 3.4 is sufficient
for stability over the entire input voltage range. Stability can
also be maintained throughout the specified load and line
conditions with 1 F film or ceramic capacitors.
November 2000
MIC5236
SHUTDOWN
ENABLE
Figure 2. Output Capacitor ESR
V
5V
Figure 1. Remote Enable
IN
5
4
3
2
1
0
200k
5
T
V
J
OUT
= 25 C
10
INPUT VOLTAGE (V)
= 10 F
IN
EN
Stable Region
MIC5236
15
200k
GND
OUT
ERR
20
25
30
C
OUT
V
V
ERR
OUT
9
Error Detection Comparator Output
The ERR 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 1.3V.
The error output has a low voltage of 400mV at a current of
200 A. In order to minimize the drain on the source used for
the pull-up, a value of 200k to 1M 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.
Reverse Current Protection
The MIC5236 is designed to limit the reverse current flow
from output to input in the event that the MIC5236 output has
been tied to the output of another power supply. See the
graphs detailing the reverse current flow with the input
grounded and open.
Thermal Shutdown
The MIC5236 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 4.7 F capacitor tied to the enable pin. The off
time is set by the 200K resistor as it recharges the 4.7 F
capacitor, enabling the regulator. This circuit reduces the
short circuit current from 280mA to 15mA while allowing for
regulator restart once the short is removed.
Voltage
Voltage
Output
Output
Figure 3. Error Output Timing
Error
Input
4.75V
1.3V
0V
5V
0V
VALID
NOT
VALID ERROR
NOT
VALID
MIC5236
Micrel