MIC2215 datasheet(13/22 Pages) MICROCHIP

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

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DS20006274B-page 13

MIC2215

The maximum junction temperature of the die (TJ(MAX))

is +125° and is also the ambient operating temperature

(TA). θJA is layout dependent; the junction-to-ambient

thermal resistance for the MIC2215 can be found in the

Temperature Specifications section.

The actual power dissipation of the regulator circuit can

be determined using the following equation:

EQUATION 5-2:

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

MIC2215 at 60°C with a minimum footprint layout, the

maximum load currents can be calculated as follows:

EQUATION 5-3:

The junction-to-ambient thermal resistance for the

minimum footprint is 43°C/W. The maximum power

dissipation must not be exceeded for proper operation.

Using a lithium-ion battery as the supply voltage

(2.8V/250 mA for channel 1, 3V/100 mA for channel 2,

and 2.8V/50 mA for channel 3), maximum power can

be calculated as follows:

EQUATION 5-4:

The calculation shows that the device is well below the

maximum allowable power dissipation of 1.511W for a

60°C ambient temperature. After the maximum power

dissipation has been calculated, it is always good

practice to calculate the maximum ambient

temperature for a 125°C junction temperature.

Calculating maximum ambient temperature follows:

EQUATION 5-5:

For more information, please refer to the Designing

with Low-Dropout Voltage Regulators Handbook.

5.9

Adjustable Regulator Application

Adjustable regulators use the ratio of two resistors to

multiply the reference voltage to produce the desired

output voltage. The MIC2215 can be adjusted from

1.25V to 5.5V, the maximum VDROPOUT, by using two

external resistors (Figure 5-1). The resistors set the

output voltage based on the following equation:

EQUATION 5-6:

FIGURE 5-1:

Adjustable Output.

PDTOTAL PDLDO1 PDLDO2 PDLDO3

Where:

PDLDO1 = (VIN1 – VOUT1) x IOUT1

PDLDO2 = (VIN2 – VOUT2) x IOUT2

PDLDO3 = (VIN3 – VOUT3) x IOUT3

PD MAX





125C 60C

–





43C/W



1.511W

PDLDO1

4.2V 2.8V

–





250mA



PDLDO1 350mW

PDLDO2

4.2V 3.0V

–





100mA



PDLDO2 120mW

PDLDO3

4.2V 2.8V

–





50mA



PDLDO3 70mW

PDTOTAL 350mW 120mW 70mW

PDTOTAL 540mW

TA MAX





TJ MAX





PD JA







–

TA MAX





125C

540mW 43C/W







–

TA MAX





101C

VOUT VREF 1 R1

-------











Where:

VREF = 1.25V

OUT1

ADJ1

MIC2215-AAA_ML

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