Micrel, Inc.

MIC5233

July 2012

10

M9999-071212-B

Maximum input voltage for a 10mA load current at 50°C

ambient temperature is 34.9V, utilizing virtually the entire

operating voltage range of the device.

Total power dissipation is calculated using the following

equation:

Eq. 4

Adjustable Regulator Application

The MIC5233BM5 can be adjusted from 1.24V to 20V by

using two external resistors (Figure 1). The resistors set

the output voltage based on the following equation:

Due to the potential for input voltages up to 36V, ground

current must be taken into consideration.

If we know the maximum load current, we can solve for

the maximum input voltage using the maximum power

dissipation calculated for a 50°C ambient, 319mV.

⎟⎟

⎠

⎞

⎜⎜

⎝

⎛

⎟

⎠

⎞

⎜

⎝

⎛

+

=

R2

R1

1

V

V

REF

OUT

Eq. 8

Feedback resistor R2 should be no larger than 300k

Ω.

Ground pin current is estimated using the typical

characteristics of the device.

619mW = VIN (102.8mA)

Eq. 6

For higher current outputs only a lower input voltage will

work for higher ambient temperatures.

Assuming a lower output current of 10mA, the maximum

input voltage can be recalculated:

Figure 1. Adjustable Voltage Application

Eq. 7