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BQ25505: Questions about BQ25505

user6242745
Prodigy 160 points
Part Number: BQ25505

Hi,

 I will have the following questions:

1. The charger only looks at the voltages on VBAT_OV every 64ms that means the VRDIV node is monitored to samples and holds the VSTOR voltage.In addition to power consumption, does this situation affect my dynamic adjustment though the resistor to set the output to dynamic output?If it is possible in theory, can my output also can be dynamically changed every 64ms?

2. According to data manual 7.4.3 shows One way to avoid cold start is to attach a partially charged storage element.If VBAT_SEC connection a depleted energy storage components such as super capacitor and energy collector provided is not enough, lead to chip cannot exit cold start, but in BQ25505 VBAT_PRI we have prepared a primary non-rechargeable batteries, we can through the primary battery to charge the  VSTOR  above 1.8 V firstly to make the circuit out of cold start, so that the booster work？I think the principle should be the same with attach a partially charged storage element, please talk about your opinion, thank you very much.

Regards,

  • 0
    TI__Guru*** 143870 points

    Hi,

    Regarding 1, the VRDIV node only samples the VSTOR node every 64ms.  It does not hold that voltage.  You can see the sampling in datasheet figure 20. If you keep the existing resistor divider and inject a dc voltage through a 3rd resistor to the existing resistor divider's midpoint, you should be able to dynamic adjust the voltage.  The concept and equations for resistor sizing are explained for different device at the link below.  You will burn power through the resistor.

    https://www.ti.com/lit/an/slyt106/slyt106.pdf

    Regarding 2, /VBAT_PRI_ON and /VBAT_SEC_ON are controlled by the VBAT_OK thresholds.  So, at a minimum, you would need the partially charged element to be above your VBAT_OK threshold in order for /VBAT_SEC_ON to be stay low after battery attach.  Keep in mind, you must attach the battery when VIN_DC, VSTOR and VBAT nodes are < 100mV from ground or the internal PFET will not turn on as explained in the middle of d/s page 17.

    Regards,

    Jeff