TPS61161: Is open circuit protection necessary

Henry Guo

Part Number: TPS61161
Other Parts Discussed in Thread: TPS61169

Hi Sirs,

Does the inductor P/N WPN4012H220MT (22UH) and the Schottky diode P/N PMEG4005AEA meet the requirement of the TPS61161 to support 3.8V Vin, 20 LEDs(4S,5Group,24V VF,100mA IF)?
Brief specification of WPN4012H220MT is 22uH +/-20%, 0.9A rated current, 0.566ohm DCR, 7MHz SRF.
Brief specification of PMEG4005AEA is 0.5A forward current, 40V reverse voltage.

In the previous project, the Schottky diode damage appeared, which seems to be high voltage breakdown.
Is the reverse voltage of diode enough?
Is open circuit protection necessary?

Thank you and Best regards,

over 4 years ago

0 Sean Zhou over 4 years ago

TI__Mastermind 22745 points

Hi Rui,

For such kind of spec, I suggest using TS61169 since this one has higher current limit spec.

Sean

0 Henry Guo over 4 years ago in reply to Sean Zhou

Prodigy 50 points

Hi,

Maybe my description is inaccurate. The total forward current is 100mA. I think tps61161 is enough.

I want to know the possible failure reasons of the diode. I think that if the LED has poor contact, the instantaneous reverse voltage that the diode bears will exceed 40V (because the open circuit voltage of tps61161 is 38V), and the diode may fail. Do you think it is reasonable ?

0 Sean Zhou over 4 years ago in reply to Henry Guo

TI__Mastermind 22745 points

Hi Henry,

Actually not, you need to calculate the average input current Iin=Vout*Iout/efficiency/Vin, for example, Ivin_avg=24V*0.1/0.85/3.8=740mA, considering the current ripple, this will larger than the N-Channel MOSFET current limit. That's the problem. And there is an AN that I published before:

http://www.ti.com/lit/an/slvaeg0/slvaeg0.pdf

Sean

0 Henry Guo over 4 years ago in reply to Sean Zhou

Prodigy 50 points

Hi,

Thank you for your guidance. I have understood the problem. Tps61169 will be used in this new project.

Finally, what are the possible causes of Schottky diode failure?

0 Sean Zhou over 4 years ago in reply to Henry Guo

TI__Mastermind 22745 points

Hi Henry,

Actually I don't have many comments on the failure of the diode. If you ahve found something, please let me know.

Sean

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TPS61161: Is open circuit protection necessary