TPS24751: TPS24751

Porselvan Muthukrishnan

Part Number: TPS24751

Hello Team,

We are using TPS24751 configured as E-Fuse in one of our designs. Attached schematics.

With Cgate - 4.7nF, Ctimer - 47nF, we see 4.2A inrush current during start up. We would like to reduce it to 0.7 Amps inrush, to meet our design requirement.

We have settled with 0.8 Amps inrush, by using dv/dt controlled inrush mode, with Cgate - 22nF, Ctimer - 180nF/220nF.

However, on the excel calculator, I see negative SOA margin with new Cgate and Ctimer values.

Could you please review this and let us know if you see any issue? Also if this doesn't work, is there a way to meet our requirement <0.8 Amps inrush requirement with minimal changes (Cgate and Ctimer).

TPS2475x_Design_Calculator_HighVin_RevA_Cgate22nF_Ctimer220nF.xlsx

over 2 years ago

0 Rakesh over 2 years ago

TI__Guru** 106611 points

Hi Muth,

Welcome to E2E!

Can you reduce the power limit setting (PLIM) and try. You can set just above the minimum recommended value (cell C39)

Best Regards,

Rakesh

0 Porselvan Muthukrishnan over 2 years ago in reply to Rakesh

Prodigy 20 points

Hi Rakesh,

Yes, It works if I set PLIM=13W in cell C40.

Is it ok to change it to 13W in the calculator, if actual PLIM = 21.992 W in Cell C70? Set by Rprog resistor.

Also do you see any issue if we use Cgate = 22nF, Ctimer = 180nF/220nF in our design? Will this impact E-Fuse functionality like overload protection and short circuit protection?

Thanks,

Porse

0 Rakesh over 2 years ago in reply to Porselvan Muthukrishnan

TI__Guru** 106611 points

On these further questions, we will check and get back by early next week.

Best Regards,

Rakesh

0 Porselvan Muthukrishnan over 2 years ago in reply to Rakesh

Prodigy 20 points

Thanks Rakesh! I will be looking forward to your reply next week.

0 Kunal Goel over 2 years ago in reply to Porselvan Muthukrishnan

TI__Guru* 79181 points

Hi Porselvan,

Yes, It works if I set PLIM=13W in cell C40.

Is it ok to change it to 13W in the calculator, if actual PLIM = 21.992 W in Cell C70? Set by Rprog resistor.

Also do you see any issue if we use Cgate = 22nF, Ctimer = 180nF/220nF in our design? Will this impact E-Fuse functionality like overload protection and short circuit protection? "

in c40 you need to enter power limit you want. C70 shows actual calculated power limit. So C70 should be close to C40. You can use Cgate and Citimer as you said as long as design passes SOA.

Regards

Kunal Goel

0 Porselvan Muthukrishnan over 2 years ago in reply to Kunal Goel

Prodigy 20 points

Hi Kunal,

Thanks for your response.

Just want to confirm this again. With "Gate Capacitor (dv/dt) Control in Inrush Mode"

Both values (13W, 22W) satisfy this equation IChg < PLIM/Vccmax. Could you please explain why one value(22W) does not pass SOA?

Ichg = 0.8A

PLIM = 13W/22W

VCC Max = 13.5

Thanks,

Porse

0 Porselvan Muthukrishnan over 2 years ago in reply to Kunal Goel

Prodigy 20 points

Hi Kunal,

Porselvan Muthukrishnan said:
Also if this doesn't work, is there a way to meet our requirement <0.8 Amps inrush requirement with minimal changes (Cgate and Ctimer).

Also please help to answer this previous question.

I don't want to change calculated power limit C70 (22W). (To bring it close to 13W, I need to change Rprog, Rset, Rimon, Rsense)

Is there a way to reduce inrush to 0.8V with minimal changes(Cgate and Ctimer)?

Thanks,

Porse

0 Kunal Goel over 2 years ago in reply to Porselvan Muthukrishnan

TI__Guru* 79181 points

Hi Porse,

Let me check and get back at earliest.

Regards

Kunal Goel

+1 Kunal Goel over 2 years ago in reply to Kunal Goel

TI__Guru* 79181 points

Hi Porse,

1. In the backend of calculator we do calculations that for the worst case stress event for the present design will the eFuse internal FET operate outside SOA. Higher power limit means chances of SOA violation are higher. 22W power limit can cause FET SOA violation here as fault time has to be set high because of lower inrush current requirements , so high power limit for higher time means SOA violation could happen.

2. You will only need to change RPROG from present design to lower power limit.

Regards

Kunal Goel

0 Porselvan Muthukrishnan over 2 years ago in reply to Kunal Goel

Prodigy 20 points

Hi Kunal,

Thanks for your reply.

Calculator shows 63.2K Rprog resistor for 13W PLIM. And SOA Pass.

We'll change only Rprog, keeping other resistor values(Rset, Rimon, Rsense) same. Please check the excel sheet attached and let's know if you see any issues.

Thanks,

Porse

5305.TPS2475x_Design_Calculator_HighVin_RevA_Cgate22nF_Ctimer220nF.xlsx

0 Kunal Goel over 2 years ago in reply to Porselvan Muthukrishnan

TI__Guru* 79181 points

Hi Porse,

It looks fine.

Regards

Kunal Goel

0 Porselvan Muthukrishnan over 2 years ago in reply to Kunal Goel

Prodigy 20 points

Thanks for the confirmation Kunal!

Power management

Power management forum

TPS24751: TPS24751