Bypass bq25504 under 1.8V

Gilen

Other Parts Discussed in Thread: BQ25504, TPS62736

Good morning,

I am using bq25504 for ultra low power energy harvesting system, and using 2.7V, 25F supercapacitor for storing the harvested energy from the solar panel. I want to power my circuit with all the charge into the supercap and function with voltages below 1.8V.

Under 1.8V in supercap the bq25504 enters in "cold start" state, and the charge of the cap is so slow. I want to bypass this bq25504 functionality. I have found a solution with some FETs in the VIN from solar panel and a comparator that is described in this link:

http://www.cap-xx.com/news/1208%20CAP-XX%20-%20Charging%20a%20Supercapacitor%20from%20a%20Solar%20Cell.pdf

In another post of this forum I have found a solution proposed by Yogesh Ramadass, with a buck converter. It seems a more elegant solution, but I don't understand it at all.

http://e2e.ti.com/support/power_management/battery_management/f/179/p/169991/626843.aspx#626843

Could anyone explain the solution proposed by Yogesh a bit clearly or attach any schematic?

Thank you and regards,

Gilen

over 12 years ago

0 Jeff F over 12 years ago

TI__Guru**** 169616 points

He means having a separate buck converter with its input tied to VSTOR and its output set to 1.8V. The TPS62736 is buck converter designed for energy harvesting apps.

0 Gilen over 12 years ago in reply to Jeff F

Intellectual 300 points

Hi Jeff,

Yogesh said that with his solution the bq25504 will always be above UV and in regular charger mode. So, it will never enter in "cold start" mode. But I don't understand that.

Will the buck converter be placed between VSTOR capacitor and VBAT? If it is step downing the voltage, how could it bypass the bq25504 1.8 V limitation? Could you explain a bit clearly or attach any schematic? I think that Yogesh is a Texas employee, could you resend those questions to him internally?

Thank you and regards,

Gilen

0 Yogesh Ramadass over 12 years ago in reply to Gilen

TI__Prodigy 205 points

Hi Gilen,

I am putting together a document to explain how to charge a supercap efficiently with our devices. I will let you know once it is ready.

Regards,

Yogesh

0 Gilen over 12 years ago in reply to Yogesh Ramadass

Intellectual 300 points

Hi Yogesh,

Thank you very much for your support.

I'll be waiting for your application note with great interest.

Best regards,

Gilen

0 Gilen over 12 years ago in reply to Gilen

Intellectual 300 points

Hi Yogesh,

Is there any news about the document to explain how to charge a supercap efficiently with bq25504?

We have an advanced design of energy hardvesting with bq25504 and we want to know your tips on this design.

Could you forward an approximate date for this document release? Or pass us a preliminary version?

Thank you and regards,

Gilen

0 Yogesh Ramadass over 12 years ago in reply to Gilen

TI__Prodigy 205 points

Hi Gilen,

I will send you a preliminary document with the essential details by end of day today. Can you please provide me your email address to send this to?

-Yogesh

0 Gilen over 12 years ago in reply to Yogesh Ramadass

Intellectual 300 points

Hi,

I have sent it to you by a "Friend request" of TI E2E Community.

Thank you for your quick answer.

Regards,

Gilen

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Bypass bq25504 under 1.8V