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BQ25895: Question regarding OTG uses

Jochem van Kranenburg
Prodigy 100 points
Part Number: BQ25895
Other Parts Discussed in Thread: TLV752

Tool/software:

Dear experts,

We're currently looking into the mentioned part and were wondering if it would be possible to use the PMID output for an integrated class D amplifier instead of for example a phone.

If I understand correctly, we can make the OTG pin high and set the OTG_CONFIG bit through I2C to disable and enable the output on PMID. What can I expect with regards to noise on the PMID output, and how is SW output affected (if it is at all)? 

The SW output will be connected directly to a TLV752 which in turn will provide the entire system with 3.3V. It's important that this 3.3V is always stable and low enough noise for an IMU and ESP32. The PMID output may fluctuate a bit, but must not result in distorted audio produced by the MAX98357.

This will work right?

Best regards,

Jochem

  • 0
    TI__Mastermind 31180 points

    Hi Jochem, 

    Thank you for reaching out via E2E. Please see my comments below. 

    Jochem van Kranenburg said:
    If I understand correctly, we can make the OTG pin high and set the OTG_CONFIG bit through I2C to disable and enable the output on PMID. What can I expect with regards to noise on the PMID output, and how is SW output affected (if it is at all)? 

    Yes OTG mode can be enabled/disabled via either pin or I2C. In forward mode operation (i.e. input adapter connected at VBUS) PMID is powered directly by DC source at the same time buck converter charges battery. In OTG mode battery directly powers SYS output while converter functions in boost mode to regulate PMID pin. In OTG boost mode max allowable current draw at PMID is 3.1A. 

    Ripple at PMID output will depend on inductor and capacitor selection in addition to nature of load. Figure 9-13 in the datasheet shows PMID regulation (CH1) when their is a load current transient. 

    Jochem van Kranenburg said:
    The SW output will be connected directly to a TLV752 which in turn will provide the entire system with 3.3V. It's important that this 3.3V is always stable and low enough noise for an IMU and ESP32. The PMID output may fluctuate a bit, but must not result in distorted audio produced by the MAX98357.

    In forward mode there is SYS_MIN regulation so that SYS will always be regulated above a minimum setting (default 3.5V adjustable through I2C). In battery only mode SYS output (same as SW output) regulation will depend on battery voltage. SYS can be lower than 3.3V if battery is allowed to discharge lower than 3.3V. 

    Best Regards,

    Garrett