MIC37300-3.3WRTR(2015) 查看數據表（PDF） - Micrel
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MIC37300-3.3WRTR Datasheet PDF : 16 Pages
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Micrel, Inc.
Input Capacitor
An input capacitor of 1.0µF or greater is
recommended when the device is more than 4 inches
away from the bulk supply capacitance, or when the
supply is a battery. Small, surface-mount chip
capacitors can be used for the bypassing. The
capacitor should be place within 1 inch of the device
for optimal performance. Larger values will help to
improve ripple rejection by bypassing the input to the
regulator, further improving the integrity of the output
voltage.
Transient Response and 3.3V to 2.5V, 2.5V to 1.8V
or 1.65V, or 2.5V to 1.5V Conversions
The MIC37300/01/02/03 has excellent transient
response to variations in input voltage and load
current. The device has been designed to respond
quickly to load current variations and input voltage
variations. Large output capacitors are not required to
obtain this performance. A standard 47µF output
capacitor, preferably tantalum, is all 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 3.7V
at the very least. The MIC37300/01/02/03 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 MIC37300/01/02/03 regulator is specified
between finite loads. If the output current is too small,
then the leakage currents dominate and the output
voltage rises. A 10mA minimum load current is
necessary for proper operation. For adjustable
regulators, this can be accomplished by selecting the
feedback resistors to load the output with 10mA.
Error Flag
The MIC37301 and MIC37303 feature an error flag
circuit that monitors the output voltage and signals an
error condition when the voltage is 5% below the
nominal output voltage. The error flag is an open-
collector output that can sink 10mA during a fault
condition.
MIC37300/01/02/03
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.
Enable Input
The MIC37301/02/03 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 VIN. When
enabled, it draws approximately 15µA.
Adjustable Regulator Design
VIN
ENABLE
SHUTDOWN
MIC37302
IN OUT
R1
EN ADJ
GND
R2
VOUT
COUT
VOUT = 1.240V 1+ RR21
Figure 1. Adjustable Regulator with Resistors
The MIC37302 and MIC37303 allow 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 VOUT − 1
1.240
Eq. 3
where VOUT is the desired output voltage. Figure 1
shows component definition. Applications with widely
varying load currents may scale the resistors to draw
the minimum load current required for proper
operation.
February 24, 2015
10
Revision 2.0
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