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BQ25570: BQ25570 Cold-Start Operating Conditions

Yong Hui Liew
Prodigy 40 points
Part Number: BQ25570

Hi, I need help understanding various sections of the BQ25570 datasheet.

1) It is mentioned that the Minimum Input Voltage for Cold start was tested under the condition VBAT < VBAT_UV. 
Would it be okay if my application initially has VBAT is greater than VBAT_UV? (When the battery is almost fully charged)



2) Why is sampling at 80%of input source voltage significant?

3) Regarding battery flags

If I understand it correctly, VBAT_OK_PROG flag will be set when VBAT decreases below VBAT_OK_HYST (max.) - 50mV right? 
What function does this serve and why do we need two flags? 


Sorry if there are too many questions, as I'm new to battery management and want to be sure. 
Appreciate any help in understanding this. Thanks!

  • 0
    Prodigy 40 points

    I have found the answer to question 2) and 3): 

    2) The MPP (maximum power point) represents the voltage at which the energy resource generates maximum power, and is represented as a percentage of the "open circuit input source voltage". For example, from the datasheet: "Solar cells typically operate with an MPP of 80% of their open circuit voltage"

    3) VBAT_OK_PROG and VBAT_OK_HYST are user-programmable flags that correspond respectively to tighter lower and upper thresholds, to signal a user to turn ON or OFF the connected system load to prevent damage to the MCU (See image below)

    All that's left is question 1) 

  • +1 in reply to Yong Hui Liew
    TI__Mastermind 18005 points

    Hello,

    Yong Hui Liew said:
    1) It is mentioned that the Minimum Input Voltage for Cold start was tested under the condition VBAT < VBAT_UV. 
    Would it be okay if my application initially has VBAT is greater than VBAT_UV? (When the battery is almost fully charged)

    That would be fine. Applying a battery with a VBAT > VBAT_UV should cause VSTOR to have a higher voltage the VSTOR_CHGEN, so the Cold Start state won't be necessary and the charger can jump right into normal boost-charging conditions.

    Best Regards,

    Juan Ospina

  • 0 in reply to Juan Ospina
    Prodigy 40 points

    Thanks for the reply Juan! It's great to hear that! 

    Also, may I confirm if VSTOR and VOUT can both be used to supply loads? I have read the datasheet, but I'm unsure if they mean VSTOR is connected "internally" to VOUT loads, or does it mean I can connect a load externally to VSTOR directly? 

    If both pins can be used to supply loads, what is the difference? 

    Appreciate the help. 

  • 0 in reply to Yong Hui Liew
    TI__Mastermind 18005 points

    Hi Yong,

    Yes, both pins can be used to supply loads. VOUT actually acts as a sort of load on VSTOR. It uses VSTOR as an input to output a regulated voltage. VOUT is just an integrated DC-DC converter, other similar loads can be attached to VSTOR.

    VSTOR is unregulated so its voltage can vary along with battery voltage, whereas VOUT should remain steady as long as VSTOR > VOUT's regulation voltage.

    Best Regards,

    Juan Ospina

  • 0 in reply to Juan Ospina
    Prodigy 40 points

    Sorry for the late reply Juan. Understood. 

    Regarding the previous response on skipping the Cold Start State by hot-plugging a battery, I'm not sure if my input source can provide the Quiescient current = 50nA. Sometimes there can be no input too. In this case, can the buck side system load still draw current from the battery directly (When EN' = 0 & VOUT_EN = 1)?


    Thanks for the help again!


  • +1 in reply to Yong Hui Liew
    TI__Mastermind 18005 points

    Hi,

    The buck side system load should be able to continue to draw current from the battery as long as battery voltage is above BAT_UV.

    Best Regards,

    Juan Ospina