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# CSD87381P: Calculation for Power loss

Part Number: CSD87381P

Hi,

Could you please let me know how to calculate Power loss based on fsw, Lout and Vout?

Datasheet Figure 1 shows Power loss vs Output current at Vout = 1.3V. Power loss is 2W when output current is 10A.

1. If Vout = 5V, can I calculate with 2W x 5/1.3 = 7.7W? Could you please let me know how to calculate Watt based on Vout?

2. Is there calculation for the power loss when user change Lout and fSW?  For example, can user calculate with 2W x (user L value) / 0.95u x (user fSW value) / 500k?

Regards,
Nagata.

• Nagata san,

Thanks for the interest in the CSD87381P.

In the datasheet there is a detailed explanation and example of how to adjust power loss for the parameters you are asking about, see page 12. Essentially you need to multiply the power loss by the normalized factor taken from the curves. Example, the stand conditions are 12Vin, 1.3Vout, 500kHz.  Standard power loss is ~2W @ 10A (from Fig1), if you only changed the Vout to 5V, then you would need to multiply 2W by normalized value in Fig 7, in this case this value is about 1.36, so PLoss would be 2*1.36= ~2.7W

There is another alternative, we recently added a power loss calculator to the web for synchronous buck applications.

The tool is located on this webpage that includes all the general MOSFET technical information here .

Go to the tools section and look for synchronous buck tool.

This tool will allow you to calculate power loss vs application conditions and will allow you to very simply trade off , size, cost and performance.

• Hi, Chris -san,

Your calculation sheet requires below controller parameter.

In this time, I will use TPS6508641. This datasheet has below parameter

Then, Are below setting correct for the calculation?

HS Pull up -> 3 ohm
HS Pull down -> 2 ohm
LS Pull up -> 3 ohm
LS Pull down -> 0.4ohm