MIC29310/29312
and the output voltage rises. A 10mA minimum load current
is necessary for proper regulation.
Adjustable Regulator Design
V
OUT
R1 = R2
×
( –—— – 1 )
1.240
Micrel
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 the table below).
Enable Input
The MIC29312 version features an enable (EN) input that
allows ON/OFF control of the device. Special design al-
lows “zero” current drain when the device is disabled—only
microamperes of leakage current
fl
ows. The EN input has
TTL/CMOS compatible thresholds for simple interfacing with
logic, or may be directly tied to V
IN
. Enabling the regulator
requires approximately 20µA of current into the EN pin.
Figure 4. Adjustable Regulator with Resistors
The adjustable regulator version, MIC29312, allows program-
ming the output voltage anywhere between 1.25V and the
15V maximum operating rating of the family. 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:
Resistor Value Table for the MIC29312 Adjustable Regulator
Voltage
2.85
2.9
3.0
3.1
3.15
3.3
3.45
3.6
3.8
4.0
4.1
Standard (Ω)
R1
100k
100k
100k
100k
100k
100k
100k
100k
100k
100k
100k
R2
76.8k
75.0k
69.8k
66.5k
64.9k
60.4k
56.2k
52.3k
48.7k
45.3k
43.2k
Min. Load (Ω)
R1
162
165
174
187
191
205
221
237
255
274
287
R2
124
124
124
124
124
124
124
124
124
124
124
Note: This regulator has a minimum load requirement. “Standard” values assume the load meets this requirement. “Minimum
Load” values are calculated to draw 10mA and allow regulation with an open load (the minimum current drawn from the load
may be zero).
MIC29310/29312
8
November 2006
MICREL [ MICREL SEMICONDUCTOR ]
