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MIC37100-1.5BM

1A Low-Voltage µCap LDO

Micrel 

Micrel, Inc.

MIC37100/37101/37102

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.

VIN

MIC37100-x.x

VOUT

IN OUT

CIN

GND

COUT

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 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.

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

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

September 2007

11

M9999-090607

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