MIC29150/29300/29500/29750
Micrel
Two resistors are used. Resistors can be quite large, up to
1MΩ, because of the very high input impedance and low bias
current of the sense comparator: The resistor values are
calculated by:
Device
Minimum Load
MIC29150 .................................................... 5mA
MIC29300 .................................................... 7mA
MIC29500 .................................................. 10mA
MIC29750 .................................................. 10mA
V
OUT
R = R
−1
1
2
1.240
Adjustable Regulator Design
Where V is the desired output voltage. Figure 4 shows
O
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
MIC29152BT
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.
V
V
OUT
IN
R1
R2
10µF
22µF
Enable Input
V
= 1.235V × [1 + (R1 / R2)]
OUT
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-
facingwithlogic, ormaybedirectlytiedto≤ 30V. Enablingthe
regulator requires approximately 20µA of current.
Figure 4. Adjustable Regulator with Resistors
Theadjustableregulatorversions, MIC29xx2andMIC29xx3,
allow programming the output voltage anywhere between
1.25V and the 26V maximum operating rating of the family.
March 2000
15
MIC29150/29300/29500/29750
MICREL [ MICREL SEMICONDUCTOR ]
