BQ25505: low-impedance power source

Wijnand Nijs

Part Number: BQ25505
Other Parts Discussed in Thread: TPL5111, BQ25570, TPS61291, TPS22860, , CC1310

Maybe a simple question: Is it possible to use a low-impedance power source (like USB or other 5V PS) to charge the battery if there is no solar/teg energy harvesting possible at that moment? With or without blokking diode.

over 5 years ago

0 Jeff F over 5 years ago

TI__Guru**** 151636 points

Wijnand,

Yes. As long as the low Z source voltage is below VBAT_OV, so that the charger is still boosting but higher than the MPP setpoint. The charger will run maximum output power, hitting peak current limit each cycle.

0 Wijnand Nijs over 5 years ago in reply to Jeff F

Prodigy 90 points

Jeff,

That's clear. At this moment we use the TPL5111/TPS22869/TPS61291 combination to save energy. If we choose for the BQ25570, is there a need for the TPS22860 (load switch) if we can disable Vout by Vout_EN controlled by the TPL5111 (system timer)?

Thanks and regards...

Wijnand Nijs

0 Jeff F over 5 years ago in reply to Wijnand Nijs

TI__Guru**** 151636 points

Wijnand,

I wouldn't think you would need the load switch since you can disable VOUT.

0 Wijnand Nijs over 5 years ago in reply to Jeff F

Prodigy 90 points

Hello Jeff,

"I wouldn't think" is not verry clear for a guru ;). I am shure somebody at TI can tell me if it's possible or not?

0 Jeff F over 5 years ago in reply to Wijnand Nijs

TI__Guru**** 151636 points

Wijnand,

I don't know your exact application or why you are using the load switch. Can you send your full schematic? How can the buck converter in the BQ25570 replace the TPS61291 boost converter?

0 Wijnand Nijs over 5 years ago in reply to Jeff F

Prodigy 90 points

iot_vt-s02c.pdf

Schematic: The VTS02C is a prefarb module with the CC1310. Furthermore the booster, system timer and power switch are following the concept of TI. This design works fine. Now we want the possibility to charge the battery with a small solar panel or alternative (USB) if there is no sun. The BQ25505 is maybe a candidate. If we can exchange the TPS61291 (booster) and TPS22860 (load switch) with the BQ25570, it would be nice.

0 Wijnand Nijs over 5 years ago in reply to Wijnand Nijs

Prodigy 90 points

Solar cell is 5.5V, battery is a Li-ion 3.7V, VCC is 3.3V

0 Wijnand Nijs over 5 years ago in reply to Wijnand Nijs

Prodigy 90 points

Or seperate the harvester and buck-booster? Is there a seperate harvester?

0 Wijnand Nijs over 5 years ago in reply to Wijnand Nijs

Prodigy 90 points

Hello Jeff,

I have ordered a nice breakout for the BQ25570 (see image) with the possibility to get the status and control the output.

If I have anny questions I will be back ;). Thanks and regards...

0 Jeff F over 5 years ago in reply to Wijnand Nijs

TI__Guru**** 151636 points

Wijnand,

Ok. Now I understand. The BQ255xx family must always be boosting, i.e., the input voltage, regulated to the panel's MPP, must be below the battery regulation voltage, VBAT_OV. If you use a panel with VOC=5.5V, its MPP of 0.8*5.5V = 4.4V is greater than your VBAT_OV = 4.2V and the BQ255xx will turn on a FET from its input, VIN_DC to pull down the panel output voltage in order to prevent battery over voltage.

If you change to a lower voltage panel but not use USB for input power or if you use two 2.5V supercapacitors in series, charged to 5V instead of a LiIon battery, then the BQ25570 would be good choice. It can also provide the 3.3V rail and both the boost charger and buck converter can be turned off putting both into a HiZ state. Please note the high voltage for the charger's /EN pin is relative to the voltage at VBAT.

The BQ25505 and BQ25570 are the only two energy harvesters, capable of regulating their input voltages to the panel's MPP, of this power level.

0 Wijnand Nijs over 5 years ago in reply to Jeff F

Prodigy 90 points

Thanks for the exelent sivice an regards...

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BQ25505: low-impedance power source