LM5170EVM-BIDIR: BOOST doesn't work but nFAUT is HIGH

Hi Minhye,

The EVM is intended for 48V-12V bidirectional applications where the 48V is applied. In your case, it seems you don't a source connected to the 48V port. If you just want to run boost, you need to delete the four breaker FETs, then solder a copper strip on to the exposed pads on the bottom side of the breaker FETs, and close the J3 jumper (labeled SYNC_R).

Thanks,
Youhao Xi, Applications Engineering.

To startup 48V boost mode from 12V battery, try to apply 48V from external source for a while to close circuit braker. Read manual point 3.4 3)

Best Regards

Piotr

LM5107EVMerror_190220.pdfNote that with the circuit breaker MOSFETs employed by the EVM, HVPS should be applied for boost
start-up. After the start-up, it can be turned off. Only after the circuit breaker MOSFETs are replaced
with a direct short across the breaker will the EVM not require the HV-PS to assist boost start-up.

In order to remove 48V power supply input I follow short between circuit breaker and J3 closed.

However boost operation not working like attached file.

Please check my setting

I already explan my goal is to enable boost supply output without 48V power supply input.

Actually I connected 48V VDC Sens J34 but opened 12V VDC Sens(J35) because I don't need buck function.

Therefore I connec CSA and 12V DC pin short in order to disable BRKG function .

Then I don't understand why I have to connect both J34 and J35 at the same time even though I want to enable boost function.

could you explain the detail algorithm ISETA circuit when J34 and J35 are shorted?

Hi Minhye,

For the EVM, even if you don't use the buck, but the buck voltage control circuit is populated, you need to close J35 to disable the buck control circuit. If J35 is not not closed, the buck voltage error amplifier will see 0V and its output could be high to take over the boost's error amplifier to control the ISETA.

J35 can only be open if you remove D9 from the EVM.

Please remove J31 jumper (labeled UVLO). Your picture is not very clear. I also need to understand what signals you connected to the EVM.

Thanks,
Youhao

Hi Youhao,

Your advice was very helpful.

LM5170EVM BOOST.pdf

I finally succeeded making high voltage with high load by remvoing J31 and removing J17-11(ISETA?) .

However I still have probelm because 2ohm 100W load with 48V port made error.

I watched ISETA signal by osciloscope by green probe.

When the 48V port is connected with 48V, ISETA didn't go to 0V and maintain 1.8V with strange oV supply.

I think it is cased by over current or other protection was enabled.

Therefore, pleasae check my EVM setup again.

Hi Minhye,

You confused me. What do you put on the 48V port? 2Ohm resistor or a 48V voltage power supply? 2Ohm resistor will be >1kW when the output gets to 50V.

Thanks,
Youhao