TPS3840-Q1: Voltage divider design for load dump of 12V battery application

Hi Jeffrey,

What you are suggesting will not work because your undervoltage trigger voltage (4V) is too low.  Is the undervoltage actually 4V or can it be higher?  If it is 4V, then I would suggest adding a zener diode to clamp the voltage to protect the TPS3840 from the load dump voltage of 42V.

Ben

Hi Ben,

 Is the undervoltage actually 4V or can it be higher? The undervoltage threshold voltage is 4V actually. It is my customer's requirement. So please review the attached schematic with clamping circuit of zener diode.

Schematic_TPS3840DL16.pdf

Regards,

Hi Jeffery,

Looking at the schematic, when the 12V rail is at ~4.9V, the output of the TPS3840-Q1 will deassert because the voltage at VDD input will be 1.7V.  The part that you are using is a TPS3840DL16-Q1 which has a 1.6V threshold with 100mV of hysteresis (VIT- + Vhys = 1.6V + 0.1V = 1.7V).  Is this the design intended to have the TPS3840-Q1 deassert at 4.9V?  

The schematic looks to be good.

Ben

Hi Ben,

My customer's design is intended to have TPS3840-Q1 deassert at 4V. Are there any change points on resistor values? Also, I think that R161 seems to be changed to more than 10kohm to reduce the leakage current. Is it correct?

Regards,

Hi Jeffery,

To better understand your customer's application, see below.  Basically, the output of the TPS3840 should go high when VBAT=4V?  Please confirm.

Ben

Hi Ben,

When VBAT is 4V under condition of falling battery voltage, the BAT_DET node goes low because /RESET pin of TPS3840-Q1 is worked as open-drain and active low. Please check it.

Regards,

Hi Jeffery,

Base on what you have mentioned, R118 resistor value is incorrect.  Please use 137K resistor.  

Ben

Hi Ben,

Thanks for your kind response. Please let me know how to calculate the value of R118.

Regards,

Hi Jeffery,

Any updates with your calculations or with the customer?

Ben

Hi Ben,

After discussion with my customer on this case, they decided the resistor values of voltage divider such as R161=36kohm or 40.2koh, R117=R118=100kohm. They will verify this design through their development process. Thanks for your support.

Regards,

Hi Jeffery,

Good luck with opportunity and glad to be of help.  Please close the thread by clicking on "resolved" if I have answered your questions.  Thanks!

Ben