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BQ25798: QON, VAC1/VAC2

Yoshinobu Kagawa
Expert 2030 points
Part Number: BQ25798

Tool/software:

1) I have a question about the relationship between Ship Mode and the /QON terminal.
    I am aware that the /QON pin can only be used to return from Ship Mode, is this correct?
    Is it correct that it is impossible to transition BQ25798 to Ship Mode using only the /QON pin?

2) We would appreciate your opinion as to whether or not there is a safety issue when a battery connected to the BAT and BATP terminals is disconnected or inserted when a valid power supply is input to VAC1 or VAC2 and the VBUS output is valid. The intent is to check if there is a possibility that the VBAT_OVP function, OCP function, etc. may operate or cause problems that impair the charging function if a battery is removed or inserted while an external power supply such as an AC adapter is connected and charging.

Regards,
Kagawa

  • 0
    TI__Guru**** 165886 points

    Hi Kagawa,

    Regarding 1, /QON can be used to exit ship or shutdown mode or cause a system reset.  The I2C host must write to the ship/shutdown register, after VBUS power source is removed, in order to enter ship/shutdown mode.

    Regarding 2, IC damage can occur if a 4S battery pack with long leads is removed/replaced, causing hotplug ringing, unless a TVS diode or external shipFET + capacitor on BATP is installed.  If charge remains enabled due to /CE pin, CE bit and no TS fault after battery removal, the charger reports BATOVP when BAT rises up to 1.03xVREG. To prevent BATOVP after battery removal, the capacitor on BAT can increased to 200uF.

    Regards,

    Jeff

  • 0 in reply to Jeff F
    Expert 2030 points

    Hi Jeff-san,

    In this case a 2S battery will be used; a 4S battery will not be used. When inserted and removed using a 2S battery and a BQ25798EVM, the VBAT OVP Flag was set to 1 when the battery was removed.
    On the register, the VBAT OVP Flag is 1, so we assume that the 2S battery is in the OVP state immediately after disconnecting the battery, but VBAT_OVP_STAT is 0 (Normal), so it is questionable whether the battery line is really in OVP.
    Please find attached the register and waveforms when the battery is disconnected, and please give us your opinion on whether there is any concern about IC damage in this condition.
    Also, if there is a possibility of IC damage due to disconnecting and inserting the battery in this state, is it correct to understand that countermeasures can be taken by increasing the capacitor between BAT and GND to a maximum of 200 µF?

    8484.waveform.zip


    Fullscreen BQ25798_register_20240605_VBAT_OPEN.txt Download 
    * Created: Wed Jun 05 10:09:43 JST 2024
*
* Format: Register Name  tab Character,\t  Register Address  tab Character,\t  Hexadecimal register value.
* BQZ Container: Charger_2_00-bq25798.bqz
*
REG00	00	10
REG01	01	320
REG03	03	64
REG05	05	6A
REG06	06	A0
REG08	08	C3
REG09	09	24
REG0A	0A	63
REG0B	0B	DC
REG0D	0D	4B
REG0E	0E	3B
REG0F	0F	B2
REG10	10	80
REG11	11	01
REG12	12	00
REG13	13	61
REG14	14	B6
REG15	15	AA
REG16	16	C0
REG17	17	06
REG18	18	54
REG19	19	3E
REG1B	1B	0B
REG1C	1C	10
REG1D	1D	40
REG1E	1E	D0
REG1F	1F	18
REG20	20	00
REG21	21	00
REG22	22	00
REG23	23	82
REG24	24	10
REG25	25	1C
REG26	26	20
REG27	27	00
REG28	28	FD
REG29	29	D7
REG2A	2A	7F
REG2B	2B	1F
REG2C	2C	FF
REG2D	2D	F4
REG2E	2E	80
REG2F	2F	00
REG30	30	00
REG31	31	01
REG33	33	00
REG35	35	2F2D
REG37	37	2F23
REG37	39	00
REG3B	3B	3AE
REG3D	3D	1B93
REG3F	3F	35A
REG41	41	2A
REG43	43	00
REG45	45	00
REG47	47	00
REG48	48	19


    Regards,
    Kagawa

  • 0 in reply to Yoshinobu Kagawa
    TI__Guru**** 165886 points

    Hi Kagawa,

    If battery is removed with charge enabled, there will always be BAT and SYS OVP events (1.03*VREG on BAT and slightly higher on SYS).  The CC loop and CV loops aren't fast enough to realize the battery has been removed so the minimum.  Adding the additional capacitance prevents the OVP event on back are removal.

    Regards,

    Jeff