ADP5043ACPZ-1-R7 datasheet(25/30 Pages) AD

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Data Sheet

ADP5043

Rev. C | Page 25 of 30

POWER DISSIPATION/THERMAL CONSIDERATIONS

The ADP5043 is a highly efficient micro PMU, and in most

cases the power dissipated in the device is not a concern.

However, if the device operates at high ambient temperatures

and with maximum loading conditions, the junction

temperature can reach the maximum allowable operating

limit (125°C).

When the junction temperature exceeds 150°C, the ADP5043

turns off all the regulators, allowing the device to cool down.

Once the die temperature falls below 135°C, the ADP5043

resumes normal operation.

This section provides guidelines to calculate the power dissi-

pated in the device and to make sure the ADP5043 operates

below the maximum allowable junction temperature.

The efficiency for each regulator on the ADP5043 is given by

100%

OUT

 

(1)

where:

η is efficiency.

PIN is the input power.

POUT is the output power.

Power loss is given by

PLOSS = PIN − POUT

(2a)

PLOSS = POUT (1-η)/η

(2b)

The power dissipation of the supervisory function is small and

can be neglected.

Power dissipation can be calculated in several ways. The most

intuitive and practical is to measure the power dissipated at

the input and all the outputs. The measurements should be

performed at the worst-case conditions (voltages, currents,

and temperature). The difference between input and output

power is dissipated in the device and the inductor. Use

Equation 4 to derive the power lost in the inductor, and from

this use Equation 3 to calculate the power dissipation in the

ADP5043 buck regulator.

A second method to estimate the power dissipation uses the

efficiency curves provided for the buck regulator, while the

power lost on the LDO is calculated using Equation 12. Once

the buck efficiency is known, use Equation 2b to derive the total

power lost in the buck regulator and inductor, use Equation 4

to derive the power lost in the inductor, and thus calculate the

power dissipation in the buck converter using Equation 3. Add

the power dissipated in the buck and in the LDO to find the

total dissipated power.

It should be noted that the buck efficiency curves are typical

values and may not be provided for all possible combinations

of VIN, VOUT, and IOUT. To account for these variations, it is

necessary to include a safety margin when calculating the

power dissipated in the buck.

A third way to estimate the power dissipation is analytical and

involves modeling the losses in the buck circuit provided by

Equation 8 to Equation 11 and the losses in the LDO provided

by Equation 12.

Buck Regulator Power Dissipation

The power loss of the buck regulator is approximated by

PLOSS = PDBUCK + PL

(3)

where:

PDBUCK is the power dissipation on the ADP5043 buck regulator.

PL is the inductor power losses.

The inductor losses are external to the device and they don’t

have any effect on the die temperature.

The inductor losses are estimated (without core losses) by

RMS

OUT1

DCR





)

(

(4)

where IOUT1(RMS) is the RMS load current of the buck regulator.

/12

)

(

OUT1

RMS

OUT1





(5)

where r is the inductor ripple current.

r ≈ VOUT1 × (1-D)/(IOUT1 × L × fSW)

(6)

D = VOUT1/VIN1

(7)

fSW is switching frequency.

L is inductance.

DCRL is the inductor series resistance.

D is duty cycle.

The ADP5043 buck regulator power dissipation, PDBUCK,

includes the power switch conductive losses, the switch losses,

and the transition losses of each channel. There are other

sources of loss, but these are generally less significant at high

output load currents, where the thermal limit of the application

will be. Equation 8 shows the calculation made to estimate the

power dissipation in the buck regulator.

PDBUCK = PCOND + PSW + PTRAN

(8)

The power switch conductive losses are due to the output current,

IOUT1, flowing through the PMOSFET and the NMOSFET power

switches that have internal resistance, RDSON-P and RDSON-N. The

amount of conductive power loss is found by:

PCOND = [RDSON-P × D + RDSON-N × (1 − D)] × IOUT12

(9)

For the ADP5043, at 125°C junction temperature and VIN =

3.6 V, RDSON-P is approximately 0.2 Ω, and RDSON-N is

approximately 0.16 Ω. At VIN = 2.3 V, these values change to

0.31 Ω and 0.21 Ω respectively, and at VIN = 5.5 V, the values

are 0.16 Ω and 0.14 Ω.

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