MIC37100/37101/37102
Micrel
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 bypass-
ing the input to the regulator, further improving the integrity of
the output voltage.
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 V
IN
or V
OUT
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.
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 V
IN
and pulled up
to the maximum supply voltage
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.
By virtue of its low-dropout voltage, this device does not
saturate into dropout as readily as similar NPN-based de-
signs. 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 without operating in dropout,
NPN-based regulators require an input voltage of 3.7V at the
very least. The MIC37100 regulator will provide excellent
performance with an input as low as 3.0V or 2.5V respec-
tively. This gives the PNP based regulators a distinct advan-
tage over older, NPN based linear regulators.
Applications Information
The MIC37100/01/02 is a high-performance low-dropout
voltage regulator suitable for moderate to high-current volt-
age 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 tran-
sistor 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 V
CE
saturation
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.
The MIC37100/01/02 regulator is fully protected from dam-
age due to fault conditions. Linear current limiting is provided.
Output current during overload conditions is constant. Ther-
mal 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.
V
IN
MIC37100-x.x
IN
C
IN
OUT
GND
C
OUT
V
OUT
Figure 1. Capacitor Requirements
Output Capacitor
The MIC37100/01/02 requires an output capacitor to main-
tain 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.
For 10µF or greater the ESR range recommended is less than
1Ω. Ultra-low ESR ceramic capacitors are recommended for
output capacitance of 10µF or greater to help improve tran-
sient response and noise reduction at high frequency.
X7R/X5R dielectric-type ceramic capacitors are recom-
mended because of their temperature performance. X7R-
type capacitors change capacitance by 15% over their oper-
ating temperature range and are the most stable type of
ceramic capacitors. Z5U and Y5V dielectric capacitors change
value by as much as 50% and 60% respectively over their
operating temperature ranges. To use a ceramic chip capaci-
tor with Y5V dielectric, the value must be much higher than an
X7R ceramic capacitor to ensure the same minimum capaci-
tance over the equivalent operating temperature range.
September 2004
11
M9999-091604
MICREL [ MICREL SEMICONDUCTOR ]
