Micrel, Inc.
MIC37100/37101/37102
much as 50% and 60% respectively over their operating
temperature ranges. To use a ceramic chip capacitor with
Y5V dielectric, the value must be much higher than an
X7R ceramic capacitor to ensure the same minimum
capacitance over the equivalent operating temperature
range.
Application Information
The MIC37100/01/02 is a high-performance low-dropout
voltage regulator suitable for moderate to high-current
voltage regulator applications. Its 500mV dropout voltage
at full load and overtemperature makes it especially
valuable in battery-powered systems and as high-
efficiency noise filters in post-regulator applications.
Unlike older NPN-pass transistor designs, where the
minimum dropout voltage is limited by the base-to-emitter
voltage drop and collector-to-emitter saturation voltage,
dropout performance of the PNP output of these devices
is limited only by the low VCE saturation voltage.
Input Capacitor
An input capacitor of 1µF or greater is recommended
when the device is more than 4 inches away from the bulk
ac supply capacitance or when the supply is a battery.
Small, surface mount, ceramic chip capacitors can be
used for bypassing. Larger values will help to improve
ripple rejection by bypassing the input to the regulator,
further improving the integrity of the output voltage.
A trade-off for the low dropout voltage is a varying base
drive requirement. Micrel’s Super βeta PNP® process
reduces this drive requirement to only 2% of the load
current.
Error Flag
The MIC37101 features an error flag (FLG), which
monitors the output voltage and signals an error condition
when this voltage drops 5% below its expected value. The
error flag is an open-collector output that pulls low under
fault conditions and may sink up to 10mA. Low output
voltage signifies a number of possible problems, including
an overcurrent fault (the device is in current limit) or low
input voltage. The flag output is inoperative during
overtemperature conditions. A pull-up resistor from FLG
to either VIN or VOUT is required for proper operation. For
information regarding the minimum and maximum values
of pull-up resistance, refer to the graph in the “Typical
Characteristics” section of the data sheet.
The MIC37100/01/02 regulator is fully protected from
damage due to fault conditions. Linear current limiting is
provided. Output current during overload conditions is
constant. Thermal shutdown disables the device when the
die temperature exceeds the maximum safe operating
temperature. The output structure of these regulators
allows voltages in excess of the desired output voltage to
be applied without reverse current flow.
MIC37100-x.x
VIN
VOUT
IN
OUT
GND
CIN
COUT
Enable Input
The MIC37101 and MIC37102 versions feature an
active-high enable input (EN) that allows on-off control of
the regulator. Current drain reduces to “zero” when the
device is shutdown, with only microamperes of leakage
current. The EN input has TTL/CMOS compatible
thresholds for simple logic interfacing. EN may be
directly tied to VIN and pulled up to the maximum supply
voltage
Figure 1. Capacitor Requirements
Output Capacitor
The MIC37100/01/02 requires an output capacitor to
maintain stability and improve transient response. As a
µCap LDO, the MIC37100/01/02 can operate with
ceramic output capacitors as long as the amount of
capacitance is 10µF or greater. For values of output
capacitance lower than 10µF, the recommended ESR
range is 200mΩ to 2Ω. The minimum value of output
capacitance recommended for the MIC37100/01/02 is
4.7µF.
Transient Response and 3.3V to 2.5V or 2.5V to 1.8V,
1.65V or 1.5V Conversion
The MIC37100/01/02 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 10µF output capacitor, is all that is required.
Larger values help to improve performance even further.
For 10µF or greater the ESR range recommended is less
than 1ꢀ. Ultra-low ESR ceramic capacitors are
recommended for output capacitance of 10µF or greater
to help improve transient response and noise reduction at
high frequency. X7R/X5R dielectric-type ceramic
capacitors are recommended because of their
temperature performance. X7R-type capacitors change
capacitance by 15% over their operating temperature
range and are the most stable type of ceramic capacitors.
Z5U and Y5V dielectric capacitors change value by as
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 or 2.5V to
1.8V, or lower, the NPN based regulators are already
operating in dropout, with typical dropout requirements
of 1.2V or greater. To convert down to 2.5V or 1.8V
M9999-090607
September 2007
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MICREL [ MICREL SEMICONDUCTOR ]
