BQ24075-Q1: Calculator issue of formula

The bq24075 is specifically designed for NTC 103AT. The temperature window can only be extand but not narrowed. This means the part is designed for 0-50C. Customer can use the RS and RP to extand the temperature window, for example to -5 to 60C. 

Dear Jing,

                Thank you for reply. But if use NTC103AT, customer use formula 3 to calculate RP as table showed above. But customer still can not get RP=845000. Do you have comments for it? Thank you.

BR

Patrick 

What is the RCOLD and RHOT value? RHOT needs to be less than 4086ohm and RCOLD needs to be greater than 28160ohm.

Have you tried with the formular? Based my calcualtion, my result matches the table by pick the closes value of standard resistor.

Dear Jing,

             Could you help provide your parameters to let us calculate based on it? Thank you. 

BR

Patrick

I use the number you highlighted in the table.

I am using excel to do the calculation by plug in the equation.

RS =(-0.0015*(C27+C28)+20*(SQRT((0.000000005625)*(C28-C27)^2+0.000105*(C28-C27))))/0.003

RP =(C31+C27)/(0.00025*C31+0.00025*C27-1)

or

RS =(-0.0015*(C27+C28)-20*(SQRT((0.005625)^2*(C28-C27)^2+0.000105*(C28-C27))))/0.003

RP =(D31+C27)/(0.00025*D31+0.00025*C27-1)

and then select between the two sets of result

RS =IF(C31>0,C31/10^3,D31/10^3)

RP =IF(C35=C31/10^3,C32/10^3,D32/10^3)

Dear Jing,

Thank you for your support. Could you also provide the excel equation file to customer for reference? Thank you.

BR
Patrick

Dear Jing,

Per above equation , could you provide your formula and schematics to us ? Due to we don't know what are C27 C28 C31 RT1 RT2. Thank you.


BR
Patrick

Dear Jing,

Additionally, customer would like cold protect point is 0°C, hot protect point is 45 °C. How to use datasheet formula to calculate right RP/RS based on 103AT NTC? Thank you.


BR
Patrick

Patrick,

The equation is the exactly the same as it in the datasheet. 

C27 = RHOT

C28 = RCOLD

Based on the calculation you will get two sets of result for RS and RP

C31 = RT1 = RS

C32 = RT2 = RP

D31 = RT1 = RS

D32 = RT2 = RP

Then comparing the two sets of result to select the final RS and RP

the final result is in C35 (RT1) and C36 (RT2)

I have mentioned multiple times already. The original temperature window for this part is 0 to 50C. This temperature window CANNOT be reduced to narrower range, ex. 0-45C.

By using the equation, it can be extended to wider range but NOT narrow.

Dear Jing,

Thank you for your kindly explanation. If customer just set hot temperature is on 45C. How to design by schematics? Or our device just only can set over 50C hot temperature point, right? Thank you.

BR
Patrick

Dear Jing,

If customer would like to do 45C hot protection of spec., do you have any solution for it? Thank you.


BR
Patrick

If the customer is looking for automotive qualified device then bq24081-q1 meets this requirement.

For non-auto qualified devices, bq2403x (power path), bq21040 (non-powerpath), or bq24081 (non-powerpath) has 0-45 ts window.