LM3658: Min input voltage

Mark Guastaferro

Part Number: LM3658

The data sheet for the LM3658 shows a different min input voltage for the AC adapter input (4.5V) vs the USB input (4.35V).

I assume this is because of the maximum charge current limit is different for these inputs. 1A for the AC adapter input and 500 mA for the USB input. The specified minimum input voltages would allow enough headroom to charge the battery to 4.2V.

My customer is limiting the charge current to 200 mA but needs to support a Vin minimum of 4.3V. If we assume that the dropout resistance of the charge control FET is the same as the 4.5V and 4.35V cases, then it seems the LM2658 could support a 4.3V input and still fully charge to 4.2V, at least at t = 25C.

Is this analysis correct?

over 4 years ago

0 Nick Brylski over 4 years ago

TI__Mastermind 19195 points

Hello Mark,

Let me confirm your analysis on the bench, you can expect to hear back later this week.

Thanks,

Nick

0 Nick Brylski over 4 years ago in reply to Nick Brylski

TI__Mastermind 19195 points

Hello Mark,

In my testing with Vin = 4.3V and charge current set to 250mA charging was ok up to 4.2V. One thing to note is that it did begin to taper current about 10-20mV earlier than a 5V supply due to the device entering dropout, but this effect was minimal.

Best regards,

Nick

0 Mark Guastaferro over 4 years ago in reply to Nick Brylski

TI__Genius 11625 points

Hi Nick,

Thanks for collecting this data. Results are good.

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LM3658: Min input voltage