BQ24800: About Schematic

Norimichi Hosogai

Part Number: BQ24800

Could you teach the connecting between Battery and VCC, please?

1．Even If Battery only boost mode support, is VCC connect to SRN directly no problem? (condition: Battery 3cell-4cell)　As below Figure 39 (Without Battery only boost).

If the above is NG , could you teach the reason, please?

２．About Battery only boost mode support schematic of Figure 18, Why connect between Battery and VCC by taking the System line?
Could you teach the reason, please?(For to support 1cell battery?)

Best regards,

over 4 years ago

0 Ethan Galloway over 4 years ago

TI__Mastermind 40106 points

Norimich,

1. VCC can connect to SRN with no problem.

2. In the battery only boost mode design, the voltage from VCC is taken from the system rail. For this design, the system rail will be boosted up. In general, we recommend attaching VCC to the highest voltage rail in the circuit. From the datasheet, VCC has a recommended operating range from 0 to 24 volts.

In conclusion for figure 19, VCC is connected to the system rail because that will be the highest voltage rail when there is no adapter. For figure 39, VCC is connected directly to the battery because that will be the highest voltage source when there is no adapter.

Regards,
Ethan Galloway

0 Norimichi Hosogai over 4 years ago in reply to Ethan Galloway

Prodigy 230 points

Thank you for your reply.

>In conclusion for figure 19, VCC is connected to the system rail because that will be the highest voltage rail when there is no >adapter.

1. In this case, Are you a recommendation connectting to the system rail to care that keeping VCC voltage is greater than REGN Regulator voltage 6.3V max? Or more higher voltage is needed for other reason?

2. About below description, is switching regulator same as REGN regulator? Or other one?

If other one, please teach the necessary supply voltage max for the switching regulator.

Best regards,

0 Ethan Galloway over 4 years ago in reply to Norimichi Hosogai

TI__Mastermind 40106 points

1. Yes. If you are using battery only boost mode, you need to power VCC from the system rail. This is so VCC is higher than REGN.

2. Other one. Switching regulator refers to the buck charger or buck regulator. To operate the buck charger, VCC needs to be higher than REGN.

+1 Ethan Galloway over 4 years ago in reply to Norimichi Hosogai

TI__Mastermind 40106 points

Norimichi,

Quick clarification on the lowest voltage the switching regulator can operate at. The datasheet lists the minimum operating voltage of the switching regulator as 4.8 volts. The max voltage of the switching regulator is 24 volts.

Thanks for being patient with the miscommunication.

Regards,
Ethan Galloway

0 Norimichi Hosogai over 4 years ago in reply to Ethan Galloway

Prodigy 230 points

Deleted

0 Ethan Galloway over 4 years ago in reply to Norimichi Hosogai

TI__Mastermind 40106 points

Norimichi,

I will research that answer for you and get back to you.

I would recommend following the EVM schematic for now.

Ethan Galloway

0 Norimichi Hosogai over 4 years ago in reply to Ethan Galloway

Prodigy 230 points

Deleted

0 Ethan Galloway over 4 years ago in reply to Norimichi Hosogai

TI__Mastermind 40106 points

Norimichi,

C3A is there for EMI filtering. R5 is there to prevent ringing on the Mosfet gate.

3. Yes, you can use a 22 uF capacitor. REGN is a linear regulator. The EVM uses a EMK107BB7225KA-T capacitor.

Regards,
Ethan Galloway

0 Norimichi Hosogai over 4 years ago in reply to Ethan Galloway

Prodigy 230 points

[deleted]

0 Norimichi Hosogai over 4 years ago in reply to Norimichi Hosogai

Prodigy 230 points

Deleted

0 Ethan Galloway over 4 years ago in reply to Norimichi Hosogai

TI__Mastermind 40106 points

Norimichi,

Yes, you can use a 8.8 uF for the REGN pin.

Regards,
Ethan Galloway

0 Norimichi Hosogai over 4 years ago in reply to Ethan Galloway

Prodigy 230 points

Thank you very much for your quick responce!

By the way, if you know, plese teach the actual maxium capacitance of REGN pin now.

I would like to know even if it is rough value.

0 Norimichi Hosogai over 4 years ago in reply to Norimichi Hosogai

Prodigy 230 points

Thank you very much for your quick responce!

By the way, if you know, plese teach the actual maxium allow capacitance of REGN pin now.

I would like to know even if it is rough value.

+1 Ethan Galloway over 4 years ago in reply to Norimichi Hosogai

TI__Mastermind 40106 points

Norimichi,

We don't spec the max allowable capacitance for the REGN pin. This is because the capacitor acts as a filter for the REGN pin. The capacitor helps smooth out voltage transients on the REGN pin.

The max capacitance is probably really high. I don't want to begin to guess at the max value could be. It could be infinite.

Ethan Galloway

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BQ24800: About Schematic