• State
  • Locked Locked
  • Replies 5 replies
  • Subscribers 64 subscribers
  • Views 304 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.

BQ51020: BQ51020 NTC query

Vignesh S
Prodigy 20 points
Part Number: BQ51020

Hi Bill,

We were trying to accommodate the thermistor in the below schematic for thermal shutdown. We have replaced the R35 with 900ohm and observed that the Transmitter is getting ON and OFF in periodic manner. On further testing we observed the below voltage at TS/CTRL pin and VTSB.

Schematic:-

 

Waveform captured at VTSB & TS/CTRL:-

Is this normal behavior once EPT happened due to overtemperature?? I was in assumption that once EPT get transfer to transmitter then there will not be any power until temperature becomes normal but in this case transmitter is ON/OFF in periodic manner.

If it is a normal behavior how can we shutdown the charging when it detects overtemperature?

  • 0
    TI__Guru* 75906 points

    Hello

    Vignesh S said:
    I was in assumption that once EPT get transfer to transmitter then there will not be any power until temperature becomes normal but in this case transmitter is ON/OFF in periodic manner.

    Bill J -- Yes the transmitter should stop power transfer for overtemp.  But the RX must be powered back on to check temp and it appears to be doing this about every 1.5 sec.

    Vignesh S said:
    If it is a normal behavior how can we shutdown the charging when it detects overtemperature?

    Bill J -- From the BQ51020 standpoint it sends EPT and TX turns off.  When the TX turns back on depends on the setting of TX.  At that point RX will check the TS pin and send EPT if needed. 

  • 0
    Prodigy 20 points

    Hi Bill,

    We have captured the BQ IC O/P against TS/CTRL pin. We have replaced R35 (refer sch in above chat) by 560ohms so that voltage at TS/CTRL should be less than 100mV and EPT packet should receive by Tx.

    But I as I mentioned in prior communication Tx is keep checking the packets in some time interval in that period some power is getting transmitted to Rx. As per waveform there are 2 pulses occurred which shows EPT but o/p goes low after 2nd pulse. why?? what is happening on first pulse?? 

    Output is low for some 1.4s and then again become high for 2.688S. 

    Can you please help here how output is sync with these pulses?

    Generally, after how much time on receiving EPT, TX starts power transfer again so that to check the overtemperature status and take action accordingly....Is it 1.5S as you mentioned in prior chat??

  • 0 in reply to Vignesh S
    TI__Guru* 75906 points

    Hello

    The TX will power up the RX.  RX will go thru start up and turn on the TS pin, it will pulse high to check NTC.  If the voltage on NTC is low (hot) for two consecutive pulsed it will send EPT to TX.   

  • 0 in reply to Bill Johns
    Prodigy 20 points

    Hi Bill,

    I did some experiment to use TS/CTRL pin  when >1.4V for EPT. Below is the circuit. But what i observed is still the device is behaving in the same way as before like charging and discharging in periodic manner. With below setup voltage at TP15 is like below waveform. Not sure why?? As per datasheet when voltage at TP15 is more than 100mV and less than 1.4V it should charge right?? I tried removing R38 but post that device is not charging itself. Is it normal??

     

     

    Br,

    Vignesh S

  • 0 in reply to Vignesh S
    TI__Guru* 75906 points

    Hi Vignesh

    As a test try pulling the AD pin high above 3.6V, this will send a different EPT to TX.

    If the NTC is setting the TS/CTRL to greater than 100mV it should be a safe condition.  Note that the NTC is only read during the pulse about every 1.4sec.

    If voltage is applied to the TS/CTRL it will take priority over the NTC votlage.