LM5066: Questions about Design Tool

Sam Ting

Part Number: LM5066

Hi Team,

We have some questions about LM5066 Design Tool,

1. Is there min. limitation for Target Fault Time when using external soft-start control?

2. Could you provide the selection consideration for the external SS PNP transistor? Can we apply "LMBTA92LT1G" instead of "MMBT5401LT1G"? Datasheet: http://www.lrc.cn/data/pdf/LMBTA92LT1G.PDF

3. Please help to review the spreadsheet if the design follows it. Thanks!

LM5066I_Design_Calculator_REV_B_+12V_20180504.xls

Best regards,

Sam Ting

over 6 years ago

0 Rakesh over 6 years ago

TI__Guru** 105361 points

Hi Sam Ting,

Thanks for reaching out. I will review and get back to you.

Best Regards,
Rakesh

0 Rakesh over 6 years ago in reply to Rakesh

TI__Guru** 105361 points

Hi Sam Ting,

1A> Higher Fault Time decreases the FET SOA margin. For a given voltage, current specification and a particular FET there will be limit on the max. fault timer period.

2A> The transistor should withdstand max. operating voltage of GATE pin. LMBTA92LT1G can be used.

3A> Design sheet looks fine.

Can you share the application and end product details.

Best Regards,
Rakesh

0 Sam Ting over 6 years ago in reply to Rakesh

TI__Expert 3560 points

Hi Rakesh,

Thanks for your support!

For question #1, we know the Max. Target Fault Time is limited by the FET SOA margin; but is there any min. limitation? Should we set it higher than Startup Time or other parameters?

Best regards,

Sam Ting

0 Rakesh over 6 years ago in reply to Sam Ting

TI__Guru** 105361 points

Hi Sam Ting,

If you use external soft-start control, there is no limitation on Min. Target Fault Time. Does this answer your question?

Best Regards,
Rakesh

0 Sam Ting over 6 years ago in reply to Rakesh

TI__Expert 3560 points

Hi Rakesh,

We want to know the reason, is it correct that the current limit or power limit is not triggered when applying external soft-start control?
The application is a power dongle to monitor the voltage & current of input source.

Best regards,
Sam Ting

0 Rakesh over 6 years ago in reply to Sam Ting

TI__Guru** 105361 points

Hi Sam Ting,

External soft-start control limits startup current to < current limit (ILIM) or current threshold (PLIM/VDS) set by power limit resistor RPWR. So, the device does not see it as fault and does not start timer.

Best Regards,
Rakesh

0 Sam Ting over 6 years ago in reply to Rakesh

TI__Expert 3560 points

Hi Rakesh,

Thanks for your support and clarification!

Best regards,
Sam Ting

Power management

Power management forum

LM5066: Questions about Design Tool