NPIZ datasheet(19/24 Pages) ENPIRION

19 / 24 page

06489

April 16, 2012

Rev: C

EN6360QI

Enpirion Confidential

www.enpirion.com, Page 19

Thermal Considerations

Thermal considerations are important power supply

design facts that cannot be avoided in the real

world. Whenever there are power losses in a

system, the heat that is generated by the power

dissipation needs to be accounted for. The Enpirion

PowerSoC helps alleviate some of those concerns.

The Enpirion EN6360QI DC-DC converter is

packaged in an 8x11x3mm 68-pin QFN package.

The QFN package is constructed with copper lead

frames that have exposed thermal pads. The

exposed thermal pad on the package should be

soldered directly on to a copper ground pad on the

printed circuit board (PCB) to act as a heat sink.

The recommended maximum junction temperature

for continuous operation is 125°C. Continuous

operation above 125°C may reduce long-term

reliability. The device has a thermal overload

protection circuit designed to turn off the device at

an approximate junction temperature value of

150°C.

The EN6360QI is guaranteed to support the full 8A

output current up to 85°C ambient temperature.

The following example and calculations illustrate

the thermal performance of the EN6360QI.

Example:

VIN = 5V

VOUT = 3.3V

IOUT = 8A

First calculate the output power.

POUT = 3.3V x 8A = 26.4W

Next, determine the input power based on the

efficiency (η) shown in Figure 8.

Figure 8: Efficiency vs. Output Current

For VIN = 5V, VOUT = 3.3V at 8A, η ≈ 94%

= POUT / PIN = 94% = 0.94

PIN = POUT / η

PIN ≈ 26.4W / 0.94 ≈ 28.085W

The power dissipation (PD) is the power loss in the

system and can be calculated by subtracting the

output power from the input power.

PD = PIN – POUT

≈

28.085W – 26.4W ≈ 1.685W

With the power dissipation known, the temperature

rise in the device may be estimated based on the

theta JA value (θJA). The θJA parameter estimates

how much the temperature will rise in the device for

every watt of power dissipation. The EN6360QI has

a θJA value of 15 ºC/W without airflow.

Determine the change in temperature (∆T) based

on PD and θJA.

∆

T = PD x θJA

∆

T ≈ 1.685W x 15°C/W = 25.28°C ≈ 25.3°C

The junction temperature (TJ) of the device is

approximately the ambient temperature (TA) plus

the change in temperature. We assume the initial

ambient temperature to be 25°C.

TJ = TA + ∆T

TJ ≈ 25°C + 25.3°C ≈ 50.3°C

With 1.685W dissipated into the device, the TJ will

be 50.3°C.

The maximum

operating junction temperature

(TJMAX) of the device is 125°C, so the device can

operate at a higher ambient temperature. The

maximum ambient temperature (TAMAX) allowed can

be calculated.

TAMAX = TJMAX – PD x θJA

≈

125°C – 25.3°C ≈ 99.7°C

The ambient temperature can actually rise by

another 74.7°C, bringing it to 99.7°C before the

device will reach TJMAX. This indicates that the

EN6360QI can support the full 8A output current

range

approximately

99.7°C

ambient

temperature given the input and output voltage

conditions. This allows the EN6360QI to guarantee

full 8A output current capability at 85°C with room

for margin. Note that the efficiency will be slightly

lower at higher temperatures and this estimate will

be slightly lower.

100

OUTPUT CURRENT (A)

Efficiency vs. Output Current

VOUT = 3.3V

CONDITIONS

VIN = 5.0V

94%

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