BQ25895: does the Chip keep its settings until the next charging?

Michael Spaeth

Part Number: BQ25895
Other Parts Discussed in Thread: TUSB422, TUSB320

Hello,

I write the registers via I2C (e.g. charging current 5 amps), then I unplug the USB cable and switch off the device (battery remains plugged in). If I now plug in the USB cable again (without I2C communication), is the charging current still at 5 amps or are the registers back to default?

In other words: does the Chip keep its settings as long as a battery is inserted or I have to rewrite the parameters via I2C before each charging process?

Thanks,

Michael

over 5 years ago

0 Jeff F over 5 years ago

TI__Guru**** 166896 points

Hi Michael,

If the watchdog timer bit continues to be written to by the host, then the charger retains the I2C register values as long as either BAT or VBUS is applied. If the watchdog timer bit expires, several registers, including charge current, are reset to safe defaults.

Regards,

Jeff

0 Michael Spaeth over 5 years ago in reply to Jeff F

Prodigy 80 points

Hi Jeff,

I have disabled the watchdog timer via I2C. So the chip would have to keep the settings regardless of the host. However, when I test on the BQ25895EVM, the charging current when plugging in the USB cable a second time is 3.7 amps instead of the set 5 amps. The default would be 2.048 amps. Do you have any idea why I'm landing at 3.7 amps?

Regards,

MIchael

0 Jeff F over 5 years ago in reply to Michael Spaeth

TI__Guru**** 166896 points

Michael,

Unless you disable them, relative VINDPM resets and D+/D- repeats (resetting input current limit) at each plug in. So you are likely being input power limited.

Regards,

Jeff

0 Michael Spaeth over 5 years ago in reply to Jeff F

Prodigy 80 points

Hi Jeff,

thank you for your prompt reply. In fact, I'm in the input current limit. 
Unfortunately, I don't understand how I can prevent resetting the input current limitation at each plug in. Can you give me a short explanation?

Regards,
Michael

0 Jeff F over 5 years ago in reply to Michael Spaeth

TI__Guru**** 166896 points

MIchael,

If you short D+=D- instead of connecting to USB bus and then change your ILIM pin resistor to the maximum input current limit that you want, the input current limit will be clamped to that limit. Alternatively, you can disable auto D+/D- in REG02b0.

Regards,

Jeff

0 Michael Spaeth over 5 years ago in reply to Jeff F

Prodigy 80 points

Hi Jeff,

your answers were helpful for understanding, but I have not yet solved my problem.

The following situation: I have a portable device with a built-in battery and a host CPU, which is connected to the BQ25895 via I²C for the initial setting of the registers. I would like the customer to be able to connect any USB-C power supply and to discuss the power supply with the BQ, at which voltage which current can be taken for charging the battery. Therefore I cannot short-circuit D + / D- and I cannot disable auto D+/D- in the register. However, if he plugs in the supplied PD power supply with enough power, the charging current should be 5A (input 12V, approx. 2.1A) and that without the CPU writing to the registers again (device should also charge when the host CPU is switched off).

I have now tried a lot of PD power supplies, but have not yet found one that automatically sets the input current limitation to 3.25A. According to Figure 9 in the data sheet, this should mean that no PD power supply unit pose as a DCP, otherwise the input current limitation should be open, right? I would like to cancel the board microcontroller, which has to overwrite the input current limit every time a power supply is plugged in.

Can my project work with the BQ25895 at all?

Regards,

Michael

0 Jeff F over 5 years ago in reply to Michael Spaeth

TI__Guru**** 166896 points

Hi Michael,

USB Type C power supplies use CC1 and CC2 lines, not D+/D- for negotiating power. The BQ25895 will not communicate with USB Type C sources. You will need to add additional circuitry (like TUSB422 or TUSB320) and software for full communication.

Regards,

Jeff

0 Michael Spaeth over 5 years ago in reply to Jeff F

Prodigy 80 points

Hi Jeff,

I understand. Thank you. One more question: in BC1.2 the maximum current is specified for DCP with 1.5A. In the BQ25895 datasheet (Figure 9 or Table 3), however, the input current limit for DCP is 3.25A. Can you explain this to me? What type of power supply does the input current limit in BQ25895 automatically set to 3.25A?

Regards,

Michael

0 Jeff F over 5 years ago in reply to Michael Spaeth

TI__Guru**** 166896 points

Michael,

At the time of this IC's release, there were some DCP-like adapters that provided more than 1.5A. The part was designed to use the ILIM pin resistor to clamp the input current to your expected/desired maximum or rely on VINDPM to prevent adapter crash.

Regards,

Jeff

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BQ25895: does the Chip keep its settings until the next charging?