• TI Thinks Resolved

BQ51050B: understanding TS/CTRL functionality

Part Number: BQ51050B

Hello,

I was trying to understand the workflow of the TS/CTRL pin for temperature protection of the  BQ51050B IC with no luck. I've read following thread  e2e.ti.com/support/power_management/wireless_power/f/693/p/400376/1536822, where a person was asking exact same question and seemed to understand how this pin works, regretfully I still couldn't fully understand it, hence I would like to ask a few questions on this subject again.

I've understood that with the equations 3 and 4 on page 24 of the DS we can calculate threshold voltages for cold and hot, which are percentage of the Vtsb. For example if I take the NTC from your example, with:

ERTJZEG103JA 
Ro = 10 kΩ, 
β = 3380,
R1 = 29.402 kΩ
R3 = 14.302 kΩ, 

I get:

V_tbs_cold = 36.4236 %
V_tbs_hot = 33.1685 %

V_tbs on the page 8 is 2.2V, that means:
V_tbs_cold = 801.32   mV
V_tbs_hot   = 729.707 mV

Are these voltages for Hot and Cold at room temperature? (although why do we need HOT and COLD at room temperature ... it's room temperature, one temperature, i.e. shouldn't there be one voltage?).

What do I do now with these values? On page 8 there are 4 threshold values ... but I still can't get it, how do I set a special threshold, e.g. if I want my chip not to charge at 45C, how do I set it up?

Also how do I choose the R1 and R3 values? It seems that it depends on the B parameter of the NTC, so it lies in Vtbs threshold limits, listed in the table on the page 8.

Anyway, one fully good explained example would be really appreciated! 

Thanks in advance,

Den

  • R1 and R3 values in data sheet page 26 are incorrect and will be changed on next revision, in work now.

    An NTC Calculator Tool has been added to the product folder--Tools & software for bq51050B, bq51051B and bq51052B.
    The tool is an excel spread sheet that can be used to calculate R1, R1&R3 and verify results.
    See below link
    www.ti.com/lit/zip/sluc629

    Best Regards,

    Bill Johns,  Applications Engineer

    Texas Instruments Inc

    Dallas, Texas