MIC5246

Micrel

MIC5246

8

June 2000

The actual power dissipation of the regulator circuit can be

determined using the equation:

P

Substituting P

conditions that are critical to the application will give the

maximum operating conditions for the regulator circuit. For

example, when operating the MIC5246-3.0BM5 at 50

°C with

a minimum footprint layout, the maximum input voltage for a

set output current can be determined as follows:

P

125 C

5

C

235 C/W

°−

°

°









0

P

The junction-to-ambient thermal resistance for the minimum

footprint is 235

°C/W, from Table 1. The maximum power

dissipation must not be exceeded for proper operation. Using

the output voltage of 3.0V and an output current of 150mA,

the maximum input voltage can be determined. Because this

device is CMOS and the ground current is typically 100

µA

over the load range, the power dissipation contributed by the

ground current is < 1% and can be ignored for this calculation.

315mW = (V

315mW = V

810mW = V

V

Therefore, a 3.0V application at 150mA of output current can

accept a maximum input voltage of 5.4V in a SOT-23-5

package. For a full discussion of heat sinking and thermal

effects on voltage regulators, refer to the Regulator Thermals

section of Micrel’s

Designing with Low-Dropout Voltage Regu-

lators handbook.

Fixed Regulator Applications

15

2

34

1

µF

MIC5246-x.xBM5

47k

Ω

Figure 1. Low-Noise Fixed Voltage Application

Figure 1 shows a standard low-noise configuration with a

47k

Ω pull-up resistor from the error flag to the input voltage

and a pull-down capacitor to ground for the purpose of fault

indication.

Dual-Supply Operation

When used in dual supply systems where the regulator load

is returned to a negative supply, the output voltage must be

diode clamped to ground.