# ADP5034 Analog Devices, ADP5034 Datasheet - Page 22

#### ADP5034

Manufacturer Part Number

ADP5034

Description

Dual 3 MHz, 1200mA Buck Regulator with Two 300 mA LDOs

Manufacturer

Analog Devices

Datasheet

1.ADP5034.pdf
(28 pages)

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ADP5034

POWER DISSIPATION AND THERMAL CONSIDERATIONS

The ADP5034 is a highly efficient 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 maxi-

mum loading condition, the junction temperature can reach

the maximum allowable operating limit (125°C).

When the temperature exceeds 150°C, the ADP5034 turns off

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

die temperature falls below 130°C, the ADP5034 resumes

normal operation.

This section provides guidelines to calculate the power dissi-

pated in the device and ensure that the ADP5034 operates

below the maximum allowable junction temperature.

The efficiency for each regulator on the ADP5034 is given by

where:

η is the efficiency.

P

P

Power loss is given by

or

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 ADP5034 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 V

I

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.

OUT.

IN

OUT

is the input power.

To account for these variations, it is necessary to include a

is the output power.

P

P

η

LOSS

LOSS

=

P

= P

= P

P

OUT

IN

IN

OUT

×

− P

100%

(1− η )/ η

OUT

IN

, V

OUT

, and

(2b)

(2a)

Rev. A | Page 22 of 28

(1)

BUCK REGULATOR POWER DISSIPATION

The power loss of the buck regulator is approximated by

where:

P

regulators.

P

The inductor losses are external to the device, and they do not

have any effect on the die temperature.

The inductor losses are estimated (without core losses) by

where:

DCR

I

where r is the normalized inductor ripple current.

where:

L is the inductance.

f

D is the duty cycle.

ADP5034 buck regulator power dissipation, P

power 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.

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

I

power switches that have internal resistance, RDS

RDS

where RDS

mately 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.

SW

OUT1(RMS)

OUT1

DBUCK

L

is the inductor power losses.

is the switching frequency.

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

ON-N

P

P

r = V

D = V

P

P

L

I

LOSS

L

DBUCK

COND

is the inductor series resistance.

OUT

is the power dissipation on one of the ADP5034 buck

≈ I

. The amount of conductive power loss is found by

is the rms load current of the buck regulator.

( 1

= P

OUT1

OUT1(RMS)

OUT1

= [ RDS

RMS

ON-P

= P

DBUCK

)

× (1 − D )/( I

/ V

COND

is approximately 0.2 Ω, and RDS

=

IN1

I

2

ON-P

OUT1

+ P

× DCR

+ P

× D + RDS

L

SW

×

+ P

L

OUT1

1

+

TRAN

12

× L × f

r

ON-N

SW

× (1 − D )] × I

)

DBUCK

Data Sheet

ON-N

ON-P

OUT1

, includes the

is approxi-

and

2

(3)

(4)

(5)

(6)

(7)

(8)

(9)