LM5576: Vin 48-57v,Vout 5V ,Iout 2A, LM5576 temperature is too high (160°F)

HI

1.based on EVM data, the efficiency is 80%, can you check how much efficiency gap between EVM and your board( it also contain the loss of inductor)

2. one thing you need to change is I don't see any input cap on your board or schematic which is close to the chip, the input cap is used to provide energy and reduce the parasitic inductor of input wire.  and you need put the ceramic cap close the Vin and GND of the chip

Thanks

Hi Daniel,

Thanks for your reply.

1. The efficiency of my board is 77%.

2. C121 and C123 are my input cap. (44 uF).

Is the temperature too high based on the situation of my board?

Hi 

based on 77%, power loss is around 3W, the roughly PCB theta JA will be 18-22, so it will have 54-66 deg C temperature raise.

if you test at room temp(25deg C), the case temp will be close to junction temp will be around 79 deg C-81deg C.

is that close to your test result?

Thanks

Hi Daniel,

Yes, The results are very close.

 I use more precise instruments to measure the efficiency.The efficiency(max) 79%.

The temperature is70-80℃。I found that diodes and inductors were the source of the heat.

I'm currently trying the following methods：

1.Increased inductance

2.Reduce switching frequency（298KHz to 100KHz）

3.Replace diodes with higher parameters

Is that feasible?

HI

the step 1 and 2 can reduce the inductor heat, normally you need let the Irate of inductor higher than Io, and control the ripple of inductor less than 40%-50% Io.

for replacing  diode,

you need the diode have smaller voltage drop at same Io and make it has good way to dissipate its power loss by optimize the layout.

thanks

Hi Daniel,

I reduced the switching frequency to 150kHz and changed the inductor to 68uh.

The efficiency is 79.5%-80.5%.

I found that the diode is the first heating device.

I'm going to use the diode with the following parameters

Is that feasible?

Thanks

Hi

Thanks for  your suggestions .

I will try tomorrow.

Thanks