ADP5040ACPZ-1-R7 datasheet(33/40 Pages) AD

33 / 40 page

Data Sheet

ADP5040

Rev. 0 | Page 33 of 40

Junction Temperature

In cases where the board temperature, TA, is known, the

thermal resistance parameter, θJA, can be used to estimate the

junction temperature rise. TJ is calculated from TA and PD using

the formula

TJ = TA + (PD × θJA)

(14)

The typical θJA value for the 20-lead, 4 mm × 4 mm LFCSP is

38°C/W (see Table 6). A very important factor to consider is

that θJA is based on a 4-layer, 4 inch × 3 inch, 2.5 oz copper, as

per JEDEC standard, and real applications may use different

sizes and layers. To remove heat from the device, it is important

to maximize the use of copper. Copper exposed to air dissipates

heat better than copper used in the inner layers. The exposed

pad (EP) should be connected to the ground plane with several

vias as shown in Figure 109.

If the case temperature can be measured, the junction temperature

is calculated by

TJ = TC + (PD × θJC)

(15)

where:

TC is the case temperature.

θJC is the junction-to-case thermal resistance provided in Table 6.

When designing an application for a particular ambient

temperature range, calculate the expected ADP5040 power

dissipation (PD) due to the losses of all channels by using

Equation 8 to Equation 13. From this power calculation, the

junction temperature, TJ, can be estimated using Equation 14.

The reliable operation of the buck regulator and the LDO

regulator can be achieved only if the estimated die junction

temperature of the ADP5040 (Equation 14) is less than 125°C.

Reliability and mean time between failures (MTBF) is highly

affected by increasing the junction temperature. Additional

information about product reliability can be found in the

Analog Devices, Inc., Reliability Handbook, which is available

at http://www.analog.com/reliability_handbook.

APPLICATION DIAGRAM

OFF

FPWM

PWM/PSM

RFILT

30Ω

PGND

MODE

10µF

1µH

VIN1

EN3

EN1

VIN2

VIN3

EN2

AGND

VOUT2

VOUT1

FB3

VOUT3

4.7µF

1µF

EN_BK

BUCK

EN_LDO1

LDO1

(DIGITAL)

EN_LDO2

LDO2

(ANALOG)

OFF

FB2

FB1

2.2µF

VOUT1 AT

1.2A

2.2µF

VIN1 = 2.3V

TO 5.5V

VIN2 = 1.7V

TO 5.5V

VIN3 = 1.7V

TO 5.5V

VOUT2 AT

300mA

VOUT3 AT

300mA

AVIN

Figure 108. Application Diagram

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