BQ25895: 5V 3A UPS, VBUS and OTG connected together

Vladimir Alexandrovich

Part Number: BQ25895
Other Parts Discussed in Thread: BQ25985, TPS2121, BQ25790

I want to make simple schematic, where a battery charger connected to the 5V bus. It should work like an UPS, I need 3A from charger back to 5V bus.

The battery charged in normal operation mode.When the power on main bus going down, charger will start to provide the 5V from the battery (OTG mode).

You can see the structural scheme below.

Pleliminary i found, that BQ25895 looks good. But i can't found how to connect OTG and VBUS pins.

I see that BQ25892 has requried functional mode, but OTG current are lower - only 2.4A. So i can't use it.

Please recommend me the solution for this case. If it'll be based on BQ25895 it'll better, but different chargers we can use too.

over 5 years ago

0 Vladimir Alexandrovich over 5 years ago

Prodigy 55 points

0 Ning T over 5 years ago in reply to Vladimir Alexandrovich

TI__Guru 57821 points

Hi,

BQ25895 should work. Please visit https://e2e.ti.com/support/power-management/f/196/t/874557 for BQ2589X: Schematic Review and PCB Layout Design Tips and https://e2e.ti.com/support/power-management/f/196/t/875386 for BQ2589x/BQ25898x FAQs.

Thanks,

Ning.

0 Vladimir Alexandrovich over 5 years ago in reply to Ning T

Prodigy 55 points

I found another one topic on e2e, where described, that BQ25985 has long startup time and it can't be fixed.
For this reason we can't use this charger in required mode, because end device will interrupted by power.

Now I'm thinking about second type of solution. I see that most chargers has system output, But almost all has range below required 5V: 3.5-4.5 V.
If I can found charger with 5V output to VSYS bus, I'll use fast power mux TPS2121 to connect it back to main rail.

Here: Charger makes VSYS with 5V on VSYS low current and charges the Li-Po Battery,
Power mux use main 5V bus as prefered source. When the main power source going down, Power mux will switch to 5V from charger. The last one will automatically switch to powering from battery, because external source was desapear.

It this solution will get the low consumption when powering from main 5V source and fast unbreackable switching to battery.

Can you recommend me the charger, which can provide 5V@3A at VSYS?

0 Jeff F over 5 years ago in reply to Vladimir Alexandrovich

TI__Guru**** 167196 points

Hi Vladimir,

You might consider the BQ25790. It has built in MUX control for external FETs.

Regards,

Jeff

0 Vladimir Alexandrovich over 5 years ago in reply to Jeff F

Prodigy 55 points

I see that VSYS of BQ25790 still can't provide the 5V on SYS pin. See the table on page 10.
Therefore I think, that I should use an external boost in addition to charger to make 5V output.

0 Jeff F over 5 years ago in reply to Vladimir Alexandrovich

TI__Guru**** 167196 points

Vladimir,

Correct. All of our NVDC chargers regulate to a MINSYS voltage but then follow the battery voltage up to battery regulation voltage.

Regards,

Jeff

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BQ25895: 5V 3A UPS, VBUS and OTG connected together