MIC29152WD datasheet(18/23 Pages) MICREL

18 / 23 page

Micrel, Inc.

MIC29150/29300/29500/29750

January 2012

M9999-013112-B

Capacitor Requirements

For stability and minimum output noise, a capacitor on

the regulator output is necessary. The value of this

capacitor is dependent upon the output current; lower

currents

allow

smaller

capacitors.

The

MIC29150/29300/29500/29750 regulators are stable

with the following minimum capacitor values at full load:

Device

Full Load Capacitor

MIC29150...............................................10µF

MIC29300...............................................10µF

MIC29500...............................................10µF

MIC29750...............................................22µF

This capacitor need not be an expensive low ESR type:

aluminum electrolytics are adequate. In fact, extremely

low ESR capacitors may contribute to instability.

Tantalum capacitors are recommended for systems

where fast load transient response is important.

Where the regulator is powered from a source with a

high AC impedance, a 0.1µF capacitor connected

between Input and GND is recommended. This capacitor

should have good characteristics to above 250kHz.

Minimum Load Current

The MIC29150–29750 regulators are specified between

finite loads. If the output current is too small, leakage

currents dominate and the output voltage rises. The

following minimum load current swamps any expected

leakage current across the operating temperature range:

Device

Minimum Load

MIC29150................................................5mA

MIC29300................................................7mA

MIC29500..............................................10mA

MIC29750..............................................10mA

Adjustable Regulator Design

VIN

VOUT

MIC29152BT

22µF

10µF

Figure 4. Adjustable Regulator with Resistors

The adjustable regulator versions, MIC29xx2 and

MIC29xx3, allow programming the output voltage

anywhere between 1.25V and the 25V. Two resistors are

used. The resistor values are calculated by:

⎟⎟

⎠

⎞

⎜⎜

⎝

⎛

−

1.240

OUT

where VOUT is the desired output voltage. Figure 4 shows

component definition. Applications with widely varying

load currents may scale the resistors to draw the

minimum load current required for proper operation (see

“Minimum Load Current” section).

Error Flag

MIC29xx1 and MIC29xx3 versions feature an Error Flag,

which looks at 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. It may sink 10mA. Low

output voltage signifies a number of possible problems,

including an overcurrent fault (the device is in current

limit) and low input voltage. The flag output is inoperative

during overtemperature shutdown conditions.

Enable Input

MIC29xx1 and MIC29xx2 versions feature an enable

(EN) input that allows ON/OFF control of the device.

Special design allows “zero” current drain when the

device is disabled—only microamperes of leakage

current flows. The EN input has TTL/CMOS compatible

thresholds for simple interfacing with logic, or may be

directly tied to ≤30V. Enabling the regulator requires

approximately 20µA of current.

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