LM74700-Q1: LM74700QDBVRQ1 NOT WORKING

fatih AS

Part Number: LM74700-Q1

Tool/software:

I used the LM74700QDBVRQ1 integration on my newly designed PCB. However, during my tests, I realized that the ideal diode was not triggered as desired.

When I looked at the design, I saw that I was acting according to the requirements. I don't understand the problem.

The features of my design are as follows;

36V input voltage

Ability to transmit current up to 10A to the output

36V Output voltage

I control the opening and closing of the line with a relay via mcu.

I am reading current with a shunt resistor on the line.

I am using SQJ476EP-T1_GE3 ( Vishay Siliconix ) as mosfet.

In my tests there is no voltage difference on Vcap ( inV outV.) = 0,5v

Even at high current there is a voltage drop of 0.5V. and the mosfet body heats up due to the diode.

note: I saw that the connections of the mosfet and ideal diode were correct and trouble-free in the tests I made.

when I connected the output 10 ohms and 5K, I saw that the system continued in the same way without triggering.

Necessary pictures are attached.

I am waiting for your help and suggestions. Thanks in advance

voltage value on Vcap

1 month ago

0 fatih AS 1 month ago

Prodigy 20 points

UPDATE:

when I powered directly from the output side of the relay on the system there was no problem and the ideal diode worked properly. now I am focusing on the relay front.

0 Shiven Dhir 1 month ago in reply to fatih AS

TI__Mastermind 46660 points

Hi Fatih,

Schematic looks fine.

Regards,

Shiven Dhir

0 fatih AS 1 month ago in reply to Shiven Dhir

Prodigy 20 points

Hi Shiven,

I have verified that the ideal diode works, but when I disconnected the relay from the PCB deb it started working. Do you have any suggestions on this? What exactly is the cause of this? Is it a magnetic relay? I couldn't solve it even by putting an external capacitor on the output? I trigger the relay directly but it doesn't work even though the relay is there.

0 Shiven Dhir 1 month ago in reply to fatih AS

TI__Mastermind 46660 points

Hi Faith,

Maybe the relay is damaged and not letting enough current to pass though and charge pump is not getting the demanded current?

Regards,

Shiven Dhir

0 fatih AS 1 month ago in reply to Shiven Dhir

Prodigy 20 points

Hello shiven,

UPDATE!

now I realized that even if I remove the relay and connect the line directly, the 74700 does not work properly. what are your suggestions? sometimes it works randomly.

0 Shiven Dhir 1 month ago in reply to fatih AS

TI__Mastermind 46660 points

Hi Faith,

I hope the device didnt get damaged due to relay.

Please replace device and test it number of times before connecting relay to verify if the circuit works fine.

Regards,

Shiven Dhir

0 fatih AS 1 month ago in reply to Shiven Dhir

Prodigy 20 points

Greetings,

I made a circuit with only lm74700 and a new IC but it didn't work. :( how is this possible?

0 Shiven Dhir 1 month ago in reply to fatih AS

TI__Mastermind 46660 points

Hi Faith,

Did you mean that the new IC isnt working as well? On the same board, new IC and doesnt work. Is it?

Regards,

Shiven Dhir

0 fatih AS 1 month ago in reply to Shiven Dhir

Prodigy 20 points

Hi, shiven,

yes and this is very strange now I will try again on the new and the unused one I will add the relevant images. thank you very much for your help.

0 Shiven Dhir 1 month ago in reply to fatih AS

TI__Mastermind 46660 points

Okay Faith

0 fatih AS 1 month ago in reply to Shiven Dhir

Prodigy 20 points

Hi,

when I disconnected it from the circuit it started working properly again LM74700.

After verifying that it was working I put the same components on the PCB again. This time it stopped working and even though there was no relay. Really interesting.

I am also attaching the PCB Designs so that we can comment. do you have any suggestions?

I am also attaching pictures of the external Circuit that works.

I give power from the green wire and GND from the emy wire and it works. I see VDD+12V on the vcap. but it did not work on the PCB.

note: there is no load on the output, even if I connect it, the result does not change.

It does not work even though I give the supply input from the input of the shunt resistor. When the relay is not in circuit :(

0 Shiven Dhir 1 month ago in reply to fatih AS

TI__Mastermind 46660 points

Hi Faith,

The layout looks fine. I hope the board isnt damaged. You can verify that with continuity tests. Also, what is the voltage that you see on VCAP-ANODE?

Regards,

Shiven Dhir

0 fatih AS 1 month ago in reply to Shiven Dhir

Prodigy 20 points

Hi shiven,

when Vcc: 28,4V
Vcap: 28,5V
Vanode: 27,80V

I think that bootstrap isnt work when on the PCB

0 Shiven Dhir 1 month ago in reply to fatih AS

TI__Mastermind 46660 points

Hi Faith,

Does this happen on multiple boards?

Regards,

Shiven Dhir

0 fatih AS 1 month ago in reply to Shiven Dhir

Prodigy 20 points

Hi, Shiven,

yes it happens on more than one PCB. I even realized that 1 of them was broken. I tried it with a new IC.

The result is the same again. bootstarp is not working.

by the way, it didn't work even though I removed everything along the line in the circuit. should I give up now? :(

even though I removed the shunt and applied power from the input of the Ideal diode, it still doesn't work.

0 Shiven Dhir 1 month ago in reply to fatih AS

TI__Mastermind 46660 points

Hi Fatih.

I have a strong feeling that the board construction has some issue. Please order our EVM and test on it.

Regards,

Shiven Dhir

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LM74700-Q1: LM74700QDBVRQ1 NOT WORKING