MIC29752BWT datasheet(15/20 Pages) MICREL

15 / 20 page

March 2000

MIC29150/29300/29500/29750

Micrel

Device

Minimum Load

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

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

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

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

Adjustable Regulator Design

VOUT = 1.235V × [1 + (R1 / R2)]

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 26V maximum operating rating of the family.

Two resistors are used. Resistors can be quite large, up to

Ω, because of the very high input impedance and low bias

current of the sense comparator: The resistor values are

calculated by:

1.240

OUT

=−









Where V

O 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 above).

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 over-

current fault (the device is in current limit) and low input

voltage. The flag output is inoperative during overtempera-

ture 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 dis-

abled—only microamperes of leakage current flows. The EN

input has TTL/CMOS compatible thresholds for simple inter-

facing with logic, or may be directly tied to

≤ 30V. Enabling the

regulator requires approximately 20

µA of current.

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