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BQ25628EVM: Input current limited during charging and VBUS_FAULT_STAT when VBUS is turned off.

Taspon Gonggiatgul
Prodigy 30 points
Part Number: BQ25628EVM
Other Parts Discussed in Thread: BQ25628,

Tool/software:

Hi,

I am currently wrapping up the driver bringup for the BQ25628 PMIC and there are currently two issues that I would like to resolve.

1. I am using the BQ25628EVM board and a 1120mA LP384260JU 3.7V lithium-ion battery for testing the driver. During charging (CC mode), I would like to maintain the charge rate around 1C. To achieve this, I have configured the ICHG_LIMIT register (0x02) with LSB = 5 << 5, MSB = 3. I did not tweak the input current limit register (0x06) so it should be kept at 3200mA. On the eval board, the ILIM_PD jumper is also connected (by default) to 2.49kOhm register, and my VIN input is with a PSU that is set to 5V/3A. When I switch the output of my PSU on, I am only getting around 0.1A output current. However, I am getting 0xC when I print out the charger status 1 register (0x1E) value, which shows that I am current in the CC phase, so I am a bit confused as to what I am doing wrong here.

2. Whenever I switch off VIN, I always get hit with a VBUS_FAULT_STAT. Upon looking closer, the datasheet says: "If VVBUS falls below VPOORSRC, the converter stops switching (if not already suspended and high due to the sleep comparator), and the VBUS_STAT transitions to 000 and the device transitions to battery-only mode". Therefore, am I correct to understand that this is the expected behavior when I remove VBUS to switch to battery only mode?

Thanks,

Taspon

  • 0
    TI__Mastermind 31840 points

    Hi Taspon, 

    Please see my comments below. 

    1) Firstly, please be aware input current limit will be the lower value between REG0x06 setting and limit set by resistor connected at ILIM pin. With 2.49kohm resistor connected input current limit will be approx. 1000mA rather than 3200mA. For your testing an easy way to ensure input current limit is in fact at max value of 3200mA is disable ILIM pin by setting REG0x19[2] = 0b (bit name 'EN_EXTILIM'). 

    Can you please help to also share register status of REG0x1D and REG0x1F? These additional status registers should hopefully help to indicate what is leading to lower output current than expected given your ICHG setting in REG0x02. Also as a sanity check of your ICHG setting what is register setting for REG0x02 and REG0x03?

    2) What is actual voltage measured at VBUS pin test point (TP10) on the BQ25628EVM when you observe VBUS_FAULT_STAT? It is expected for device to switch to battery only mode when input supply is removed (or turned off in your case), but VBUS_FAULT_STAT should output 'normal' status (0b) once VBUS voltage decays due to input supply being turned off. 

    Best Regards,

    Garrett 

  • 0 in reply to Garrett Kreger
    Prodigy 30 points

    Hi Garrett,

    Thank you for the prompt response.

    1) I understand that the current limit is the lower of the two, so I decided to leave 0x06 unchanged and only rely on R_Lim (2.49kOhm) to set the current limit. My reg status for 0x1D, 0x1E, and 0x1F are 0x40, 0x0c, 0x00. For 0x02 I have 0xA0 and for 0x03 I have 0x03, so the charge current should be 29 * 40 = 1160mA. Right now, my RIGOL DP832 PSU is only showing 0.29A of output current at 5V/3A

    2) OVP on the charge fault register actually only appears once when I turn off the supply, so from what you are saying it looks like this is the expected behavior if I am only getting this once whenever I am turning off the output of my PSU?

    Thanks,

    Taspon

  • 0 in reply to Taspon Gonggiatgul
    TI__Mastermind 31840 points

    Hi Taspon, 

    Thank you for your response. 

    1) I can confirm 0x02 = 0xA0 and 0x03 = 0x03 will set ICHG to 1160mA. Unfortunately the reg status shared do not indicate a reason why power draw to BQ25628 is lower than expected. 

    Given this can you please help to share a full register log from the BQ25628 IC while attempting to charge so I can review? As part of this register log can you take a single ADC measurement as well for reference. ADC is enabled by setting REG0x26[7] = 1b. Additionally, do you disable the watchdog timer in REG0x16 to ensure ICHG setting is not unintentionally being reduced? 

    2) Thanks for further clarification. I agree there is no concern. VBUS_FAULT_STAT indicates both input OVP and undervoltage (called 'sleep' in reg map description). If input voltage reduces at a slow enough rate observing this fault register once is expected. 

    Best Regards,

    Garrett