MIC29310/29312

Micrel

MIC29310/29312

8

November 2006

and the output voltage rises. A 10mA minimum load current

is necessary for proper regulation.

Adjustable Regulator Design

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:

R1 = R2

× ( –—— – 1 )

1.240

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 flows. The EN input has

TTL/CMOS compatible thresholds for simple interfacing with

requires approximately 20µA of current into the EN pin.

Voltage

Standard (Ω)

Min. Load (Ω)

R1

R2

R1

R2

2.85

100k

76.8k

162

124

2.9

100k

75.0k

165

124

3.0

100k

69.8k

174

124

3.1

100k

66.5k

187

124

3.15

100k

64.9k

191

124

3.3

100k

60.4k

205

124

3.45

100k

56.2k

221

124

3.6

100k

52.3k

237

124

3.8

100k

48.7k

255

124

4.0

100k

45.3k

274

124

4.1

100k

43.2k

287

124

Resistor Value Table for the MIC29312 Adjustable Regulator

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).