MIC5259-2.85BML datasheet(9/11 Pages) MICREL

9 / 11 page

Micrel, Inc.

MIC5259

September 2006

M9999-091406

The actual power dissipation of the regulator circuit can

be determined using the equation:

PD = (VIN – VOUT) IOUT + VIN IGND

Substituting PD(max) for PD and solving for the operating

conditions that are critical to the application will give the

maximum operating conditions for the regulator circuit.

For example, when operating the MIC5259-2.8BML at

70°C with a minimum footprint layout, the maximum

input voltage for a set output current can be determined

as follows:

⎟

⎠

⎞

⎜

⎝

⎛

−

C/W

125

PD(max)

PD(max) = 611mW

The junction-to-ambient thermal resistance for the

minimum footprint is 90°C/W, from Table 1. The

maximum power dissipation must not be exceeded for

proper operation. Using the output voltage of 2.8V and

an output current of 200mA, the maximum input voltage

can be determined. Because this device is CMOS and

the ground current is typically 110µA over the load

range, the power dissipation contributed by the ground

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

611mW = (VIN – 2.8V) 200mA

611mW = VIN × 200mA – 560mW

1171mW = VIN × 200mA

VIN(max) = 5.85V

Therefore, a 2.8V application at 200mA of output current

can accept a maximum input voltage of 5.85V in an MLF

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 Regulators

handbook.

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