MIC37100-3.3WS

Micrel, Inc. 

MIC37100/37101/37102

 

  

September 2007

 

11 

M9999-090607 

 

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. 
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 
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

IN

OUT

GND

C

IN

C

OUT

V

IN

V

OUT

 

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. 
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 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 

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. 

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. 

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 
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 

MIC37100-3.3WS Datasheet Related Products:
MIC37100-3.3WS Information:
Part No.
MIC37100-3.3WS
Description
IC REG LDO 3.3V 1A SOT223
File Size
718955 bytes
Page Size
612 x 792 pts (letter)
All Pages
15
Manufacturer
Micrel, Inc.
Homepage
http://www.micrel.com/
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