Datasheet

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:
P
D
= (V
IN
− V
OUT
)I
OUT
+ V
IN
× I
GND
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
1VV
REFOUT
Eq. 8
P
D(MAX)
= (V
IN
− V
OUT
)I
OUT
+ V
IN
× I
GND
where V
REF
= 1.24V.
319mW = (V
IN
− 3V)100mA + V
IN
× 2.8mA Eq. 5
Feedback resistor R2 should be no larger than 300kΩ.
Ground pin current is estimated using the typical
characteristics of the device.
619mW = VIN (102.8mA)
V
IN
= 6.02V 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
319mW = (V
IN
− 3V)10mA + V
IN
× 0.1mA
349mW = V
IN
× 10.1mA
V
IN
= 34.9V Eq. 7