MIC37501_11 Datasheet, PDF (9/11 Pages) Micrel Semiconductor – 5A, Low Voltage μCap LDO Regulator

Micrel, Inc.
that is required. Larger values help to improve
performance even further.
By virtue of its low dropout voltage, this device does
not saturate into dropout as readily as similar NPN-
based designs. When converting from 3.3V to 2.5V,
2.5V to 1.8V or 1.65V, or 2.5V to 1.5V, the NPN-
based regulators are already operating in dropout,
with typical dropout requirements of 1.2V or greater.
To convert down to 2.5V without operating in dropout,
NPN-based regulators require an input voltage of at
least 3.7V. The MIC37501/02 regulator will provide
excellent performance with an input as low as 3.0V or
2.25V, respectively. This gives the PNP-based
regulators a distinct advantage over older, NPN-based
linear regulators.
Minimum Load Current
The MIC37501/02 regulator is specified between finite
loads. If the output current is too small, leakage
currents dominate and the output voltage rises. A
10mA minimum load current is necessary for proper
operation.
Error Flag
The MIC37501 features an error flag circuit that
monitors the output voltage and signals an error
condition when the voltage drops 5% below the
nominal output voltage. The error flag is an open-
collector output that can sink 10mA during a fault
condition.
Low output voltage can be caused by a number of
problems, including an overcurrent fault (device in
current limit) or low input voltage. The flag is
inoperative during overtemperature shutdown.
MIC37501/37502
Enable Input
The MIC37501/02 also features an enable input for
on/off control of the device. Its shutdown state draws
“zero” current (only microamperes of leakage). The
enable input is TTL/CMOS-compatible for simple logic
interface, but can be connected up to V_IN. When
enabled, it draws approximately 15µA.
Adjustable Regulator Design
V_IN
ENABLE
SHUTDOWN
MIC37502
IN OUT
R1
EN ADJ
GND
R2
V_OUT
C_OUT
V_OUT = 1.240V ^{⎛⎝⎜}1+ _RR21^{⎞⎠⎟}
Figure 2. Adjustable Regulator with Resistors
The MIC37502 allows programming the output voltage
anywhere between 1.24V and the 5.5V maximum
operating rating of the family. Two resistors are used.
Resistors can be quite large, up to 1MΩ, because of
the very high input impedance and low bias current of
the sense comparator.
The resistor values are calculated by:
R1
=
R2_{⎜⎜⎝⎛}
V_OUT
1.240
−
1_{⎟⎟⎠⎞}
Where V_OUT is the desired output voltage. Figure 2
shows component definition. Applications with widely
varying load currents may scale the resistors to draw
the minimum load current required for proper
operation (see above).
May 2011
9
M9999-050511-B