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ADP5033

Rev. 0 | Page 15 of 28

POWER DISSIPATION AND THERMAL CONSIDERATIONS

The ADP5033 is a highly efficient micropower management

unit (μPMU), and, in most cases, the power dissipated in the

device is not a concern. However, if the device operates at high

ambient temperatures and maximum loading condition, the

junction temperature can reach the maximum allowable

operating limit (125°C).

When the temperature exceeds 150°C, the ADP5033 turns off

all the regulators, allowing the device to cool down. When the

die temperature falls below 130°C, the ADP5033 resumes

normal operation.

This section provides guidelines to calculate the power dissi-

pated in the device and ensure that the ADP5033 operates

below the maximum allowable junction temperature.

The efficiency for each regulator on the ADP5033 is given by

100%

OUT

(1)

)

is the rms load curren

where:

is the efficiency.

is the input power.

POUT

is the output power.

Power loss is given by

PLOSS

= PIN − POUT

(2a)

PLOSS

= POUT (1− η)/η

(2b)

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. Perform the measurements 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 ADP5033 buck converter.

A second method to estimate the power dissipation uses the

efficiency curves provided for the buck regulator, and the power

lost on each LDO can be calculated using Equation 12. When

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 then calculate the

power dissipation in the buck converter using Equation 3. Add

the power dissipated in the buck and in the two LDOs to find

the total dissipated power.

Note 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

BUCK REGULATOR POWER DISSIPATION

The power loss of

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

by Equation 12.

the buck regulator is approximated by

(3)

PDBU

rs.

r losses are external to the device, and they do not

ature.

(4)

DCR

t of the buck regulator.

PLOSS

= PDBUCK1 + PDBUCK2 + PL

where:

is the power dissipation on one of the ADP5033 buck

regulato

is the inductor power losses.

The inducto

have any effect on the die temper

The inductor losses are estimated (without core losses) by

PL ≈ IOUT1(RMS)

2 × DCRL

where:

is the inductor series resistance.

IOUT1(RMS

)

(

OUT1

RMS

OUT

(5)

where r is the inductor ripple cur

r ≈ VOUT1 × (1 − D)/(IOUT1 × L × fSW)

(6)

witching frequency.

(7)

lator power dissipation, PDBUCK, includes the

pow

(8)

to the output current,

IOUT

(9)

mate

ren

where:

L is the inductance.

fSW is the s

D is the duty cycle.

D = VOUT1/VIN1

ADP5033 buck regu

er switch conductive losses, the switch losses, and the transi-

tion 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 is. Equation 8

captures the calculation that must be made to estimate the

power dissipation in the buck regulator.

PDBUCK = PCOND + PSW + PTRAN

The power switch conductive losses are due

, flowing through the P-MOSFET and the N-MOSFET

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

where RDSON-P is approximately 0.2 Ω, and RDSON-N is approx

ly 0.16 Ω at 125°C junction temperature and VIN1 = VIN2 =

3.6 V. At VIN1 = VIN2 = 2.3 V, these values change to 0.31 Ω and

0.21 Ω, respectively, and at VIN1 = VIN2 = 5.5 V, the values are

0.16 Ω and 0.14 Ω, respectively.

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