• State TI Thinks Resolved
  • Locked Locked
  • Replies 2 replies
  • Answers 1 answer
  • Subscribers 63 subscribers
  • Views 1501 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

BQ25570 Supercapacitor connected to VSTOR and VBAT Floating

Hardik Parmar
Prodigy 220 points
Other Parts Discussed in Thread: BQ25570

Hello,

In my application, I do not want to recharge battery so i connected a super capacitor to VSTOR not VBAT. I made this VBAT pin floating because Buck, Boost & VOUT is monitored by VSTOR voltage threshold not VBAT.  

Is it okay to connect  a super capacitor to VSTOR as a storage element?  System load is connected to VOUT pin.  

Application requirements:

VOUT: 3V

VBAT_OV : 4.2V

Application is using VBAT_OK to turn on/off the system load connected to VOUT. What are the limitations to such a system?  Please give me some suggestions.

  • 0
    TI__Guru**** 166156 points
    Hi Hardik,

    The FET between VSTOR and VBAT is intended to prevented over discharge as set by the VBAT_UV threshold. If the supercapacitor does not have an overdischarge minimum voltage then there is no need to connect to VBAT. Keep in mind that start up using the cold start circuit (VSTOR<1.8V)will be extremely slow with such a large capacitor on VSTOR. You might consider configuring your circuit as explained here www.edn.com/.../Fast-charging-a-supercapacitor-from-energy-harvesters with the supercapacitor at VOUT.
  • 0 in reply to Jeff F
    Prodigy 220 points
    Thanks Jeff!
    Yes I agree with your answer that we have to use such a large capacitor to VSTOR which can slow down the cold start to VBAT_UV threshold duration. As we need burst of power into our system for a small duration of time like turn on/off load and BQ25570 controlled by a MOSFET switch using external supply(MCU) acknowledged by VBAT_OK. VIN_DC is continuous 0.7 to 1.1V. I chose AVX SCM series supercapacitor with High pulse power capability, Low ESR and Low leakage current. What type of capacitor would you recommend if load power consumption is 50mW with on time 100ms. I am planning to use 1000uF 25V(Electrolyte), 0.47F 5V (Supercapacitor AVX SCM series), 0.01F 5.5V (KEMET Supercap).

    VBAT_OK toggles when threshold crosses VBAT_OK_HYST and VBAT_OK. duration of this toggling is internally set (64ms)? or it depends on voltage crossover time period.

    I will look into this link and perform this supercapacitor at VOUT, www.edn.com/.../Fast-charging-a-supercapacitor-from-energy-harvesters.

    Thanks Again.