BUF12840: Output Source/Sink Current

hideyuki sakai

Mastermind 6250 points

Part Number: BUF12840
Other Parts Discussed in Thread: BUF16821

Dear, Sir.

My customer is evaluating BUF12840. At this time, I would like to make sure about

output source/sink current. Please give your advice.

They are using 1ch output under 104mA source/sink.

Other 11ch are using several mA, only.

They have measured Tc temperature, it was 50 deg.C under Ta=25 deg.C.

Is it no problem to use over 100mA output source/sink for 1ch to be well

considered about the heating issue?

Best Regards,

H. Sakai

over 6 years ago

0 Aaron Goodson over 6 years ago

TI__Expert 6330 points

Hi,

I have notified our expert regarding this topic. Please expect a response by 7/30/19.

Thanks,

Aaron

0 Costin Cazana over 6 years ago

TI__Expert 4940 points

Hello,

The temp measured on the package is not exactly same as the junction temp.

My suggestion is to measured the supply current and to calculate the total power dissipation.

The internal junction temperature Tj=Tamb+Pwr*Rtj.

Since board, power pad assembly affect Rtj, my recommended Rtj is 40C/W . This is slightly higher than datasheet Rtj=35.6C/W, it is safer to have same margin

The calculated Tj should be <125C for the worst ambient temperature

Regards,

Costin

0 hideyuki sakai over 6 years ago in reply to Costin Cazana

Mastermind 6250 points

Dear, Costin-san.

Thank you so much for your advice.

I would like to double-confirm about the total power dissipation calculation.

Do you mean that ;

Total power dissipation = (Vvsd * Ivsd) + (Vvs * Ivs) ?

Or there was other calculation formula?

Best Regards,

H. Sakai

0 Costin Cazana over 6 years ago in reply to hideyuki sakai

TI__Expert 4940 points

Sakai san,

That's correct.

Regards,

Costin

0 hideyuki sakai over 6 years ago in reply to Costin Cazana

Mastermind 6250 points

Dear, Costin-san.

Thank you so much for all of your advice.

I would like to confirm following. Sorry again & again.

1. Don't need to care the current source or sink setting for power dissipation calculation?

2. You recommended Rth-ja. The other side, the datasheet is defined ψJT.

I wonder which is better?

Best Regards,

H. Sakai

0 Costin Cazana over 6 years ago in reply to hideyuki sakai

TI__Expert 4940 points

Hi Sakai san,

Theta_ja is the relevant number for the junction temperature. To be conservative, I'm suggesting 40C/W ( spec 35.6C/W)

Tj=Tamb+Rtj*Power_IC

The power dissipated in the IC is power supply power minus external load power. The digital power has very small contribution, can be ignore

I run an experiment using a similar part- BUF16821:

Vs=12V

- load on Vcom, the other outputs have no load

-Vcom set to 12V(full scale) and 6V(1/2 scale)

-Vcom load: open; 121ohm;60ohm;30.1ohm

Rtj=40C; Tamb=18C

Last column is the expected junction temp

Regards,

Costin

0 Costin Cazana over 6 years ago in reply to Costin Cazana

TI__Expert 4940 points

missing table

Regards,

Costin

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BUF12840: Output Source/Sink Current