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TIDA-01093: Zener diode D59 voltage rating

Danilo A.
Mastermind 25535 points
Part Number: TIDA-01093

Hi Team,

According to the E2E thread below, for a 20-cell battery, the BAT+ would be around 60 to 80V. Our customer would like to know why the voltage rating of the zener diode D59 is 91V. 

https://e2e.ti.com/support/tools/simulation-hardware-system-design-tools-group/sim-hw-system-design/f/simulation-hardware-system-design-tools-forum/899807/tida-01093-schematic-check?tisearch=e2e-sitesearch&keymatch=TIDA-01093%25252520vbat#

Regards,

Danilo

  • 0
    TI__Guru 54715 points

    Hi Danilo,

    The author of TIDA-01093 did not explain the circuit with D59.  Q53 is used as a level shifter for the ALERT signal from the top device to the bottom.  In the case of transients on he battery beyond the nominal voltage the 91V rating of D59 will limit before the 100 V rating of Q53. D56 and D2 will also limit voltages in that path with extra appearing across Q56 Vgs.  Depending on your transients you might want to limit the drain voltage from the BAT+ with D59 and add a drain resistor to accept any extra voltage drop during the transient.  Use a topology suitable for your system and the transients it will experience.