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BQ25798: BQ25798 PMID PATH

Agxin Justin xavier
Intellectual 350 points
Part Number: BQ25798
Other Parts Discussed in Thread: BQ25731

Tool/software:

I am planning to use this part for An application where in VBUS voltage is 15V 

I have the battery of 2s2p 8.4 volt max all the configuration is programmed based on 2s2p with charging current of 2.5A and safe discharging of 5A

now CPU and other loads are connected to a VSYS ,I have a requirement of charging a E-cap to 15V for a LED circuit During 15V charger plug in I am able to use the PMID pin voltage to charge the E-CAP 

When charger is removed can i boost the battery voltage to 15v  and get this in PMID pin ? what is the limitation of the current when USB charger is plugged and during this backup boost mode how to configure and use this mode please help 

  • 0
    TI__Expert 5695 points

    Hi Justin,

    Agxin Justin xavier said:
    During 15V charger plug in I am able to use the PMID pin voltage to charge the E-CAP 

    From my understanding of this application, there is a 2S2P battery connected to BAT, and an E-CAP connected to PMID? The converter will not be able to regulate current from the charger plugging in to the PMID pin. If there is too much inrush current, this could damage the device.

    Agxin Justin xavier said:
    When charger is removed can i boost the battery voltage to 15v  and get this in PMID pin ? what is the limitation of the current when USB charger is plugged and during this backup boost mode how to configure and use this mode please help 

    The charger can boost the battery voltage to 15V on the PMID pin. I do not think the PMID load current will be regulated, so the current limitation will be on the safe discharge limit for the battery, in your case 5A. Since the voltage is boosting, the current limitations on the PMID pin will be lower than 5A.

    Best regards,
    Michael

  • 0 in reply to Michael Bradbourne
    Intellectual 350 points

    Hi Michael ,

    Thanks for the response 

    The converter will not be able to regulate current from the charger plugging in to the PMID pin. If there is too much inrush current, this could damage the device. 

    For direct path from charger plugged in USB to PMID need to limit the current at the PMID pin externally 

    But for the VBAT to PMID boost the current is limited to battery discharge limit circuitry got this clarified 

    Now let say I have VSYS powering the system and Vbat supplied by battery PMID used for charging a cap using a charger BQ25731(which i think can limit input current)

    The PMID power for Vsb path is always present but when VBUS is not present the charger can cut VBUS PATH by disabling the external VAC  input mosfet and can boost the voltage to 15v ,will this transaction from vbus SOURCE  path to vbat SOURCE BOOSTED path is seamless or will have delay my vbus can vary from 15v 3a to 5v 3a.what is the procedure from the host to do this ?or this process can be automatically from charger ?

     

  • 0 in reply to Agxin Justin xavier
    TI__Expert 5695 points
    Agxin Justin xavier said:
    For direct path from charger plugged in USB to PMID need to limit the current at the PMID pin externally 

    This is correct if there is a load on the PMID pin.

    Agxin Justin xavier said:
    will this transaction from vbus SOURCE  path to vbat SOURCE BOOSTED path is seamless or will have delay my vbus can vary from 15v 3a to 5v 3a

    This can be seamless if you set EN_BACKUP=1 and add a little more capacitance to the pin. Take a look at section 9.3.7.2 Backup Power Supply Mode in the datasheet for more information.

    Best regards,
    Michael