LM5121: Removing the disconnect MOSFET

Danilo A.

Part Number: LM5121
Other Parts Discussed in Thread: LM5122

Hi Team,

We have received this inquiry from our customer.

I noticed that in one of the forums LM5121 can be used without Qd mosfet, but the forum doesn't explain how.

https://e2e.ti.com/support/power-management-group/power-management/f/power-management-forum/751198/lm5121-is-qd-nmosfet-mandatory?tisearch=e2e-sitesearch&keymatch=LM5121#

I originally had LM5121 in my design but with current supply issues that part is not available

my original design has an LM5122 20 pin TSSOP, already a working unit, but these LM5122 are not available.

I'm trying to see if using an LM5121 20 pin TSSOP, with minimal red-wiring or none, nor using the disconnect mosfet, will work for me. if so, how?

Regards,

Danilo

over 3 years ago

+1 Richard Fu22 over 3 years ago

TI__Mastermind 31315 points

Hi Danilo,

If you want to remove the Qd MOSFET, please place a 100pF capacitor in between the DG and DS pin, and then place a 500kOhm switch from DS pin to GND if disconnection switch is not used.

Regards,

Richard

0 Danilo A. over 3 years ago in reply to Richard Fu22

TI__Mastermind 30040 points

Hi Richard,

Thank you for this instruction. Our customer would like to clarify about the 500K ohm switch. According to our customer,

By 500K ohm switch, do you mean a toggle switch? Can you clarify what switch?

Regards,

Danilo

+1 Richard Fu22 over 3 years ago in reply to Danilo A.

TI__Mastermind 31315 points

Hi Danilo,

Please disregard the switch, I accidentally mistyped. It's 500kOhm resistor.

Regards,

Richard

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LM5121: Removing the disconnect MOSFET