LM2585: About the internal logic.

Kengo.Y

Guru 11255 points

Part Number: LM2585

Hi team.

I have some questions about the internal logic for LM2585.

My customer refer to snva005b(p.7) and configure the flyback.

1. About the soft start.

If a momentary power failure occurs and the input voltage has a residual voltage of several V, will soft start start if the input voltage is restored even if the COMP pin voltage is 0V?

　I think soft-start will not restart unless the device is turned off.

2. About the control logic for SWpin.

I'd like to know about the movement for SWpin.

Does the logic movement for FB(COMPpin) match below?

3. If you have something document about the movement for internal logic, could you share us?

I would like to know the logic control for the movement of each comparator.

Sincerely.

Kengo.

over 5 years ago

0 Richard Fu22 over 5 years ago

TI__Mastermind 31315 points

Hi Kengo,

Here are my responses to your question:

1) Per the application note you've set up, it looks like once soft-start is run, soft-start comparator is then disabled and overcurrent protection is enabled. As such, soft-start should not start up again until you turn Vin off. Please refer to this thread for more insight into SS behavior:

https://e2e.ti.com/support/power-management/f/196/p/302300/1055575?tisearch=e2e-sitesearch&keymatch=LM2585#1055575

2) A,B,C match expected behavior per datasheet page 11. SW pin will look different due to how control logic is implemented in that block.

3) There is no current document for the internal logic available since this is proprietary information.

Thanks,

Richard

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LM2585: About the internal logic.