Because of the holidays, TI E2E™ design support forum responses will be delayed from Dec. 25 through Jan. 2. Thank you for your patience.

  • State Resolved
  • Locked Locked
  • Replies 2 replies
  • Subscribers 64 subscribers
  • Views 836 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

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.

BQ76200: Zener and TVS diodes

Mikhail Ipatev
Prodigy 60 points
Part Number: BQ76200

Hello.
Please tell me, is it possible to use zener diodes to protect the gates of MOSFETs as shown in the figure (red circles)?


I have doubts that with closed transistors VT12 and VT13, with a large voltage surge from the side of the charger or load,

too much current may flow through the VDZ12 -> R89 circuit, which will damage the driver chip.


Is it possible to install a zener diode to protect the gates of charging MOSFETs (a bunch of VDZx and Rb in the figure)?

I have doubts that with transistors VT9 and VT10 closed, current will flow through the VDZx -> Rb circuit, which will increase

the self-discharge of the battery.


And is it possible to use a bidirectional TVS diode (VDZ16) at the battery output, , or should I use a unidirectional one?

  • +1
    TI__Mastermind 37670 points

    Hello Mikhail,

    Yes, you can use Zener diodes as you have circled for the DSG/CHG FETs. For the PCHG FET however the Zener (VDZ9) should be flipped, as this is a PFET. If the PCHG FET were to attempt to turn on, it would forward-bias this Zener and the PFET would not turn-on.

    You are correct, although the part does not have a max current into the pin, too much current flowing through VDZ12 to R89 could potentially damage the device. You must choose a suitable R89 resistance to limit the current. Your resistance seems okay to me for this. I would recommend reading our bq76200 Beyond the Simple Application Schematic application note. Which goes into detail for the gate resistance and talks about using Zeners for FET protection (Section 4.2 Protecting the FET Gate and DSG Pin).

    The CHG Zener is also discussed in Section 5 CHG Circuit of this application note.

    From what I understand, during normal operation the Zeners would not conduct much, if the FETs are ON, the device will drive the gate-source voltage to ~12-V, Zeners will be OFF. If the FETs are OFF, the device will drive the voltage to ~0-V across the gate-source (The CHG pin will connect to the BAT pin when OFF, The DSG pin will connect to the PACK pin when OFF), so Zeners would be OFF. During transients, consumption could be increased.

    Yes, you can use a bidirectional TVS diode.

    Best Regards,

    Luis Hernandez Salomon

  • 0 in reply to Luis H. S.
    Prodigy 60 points 
    Thank you very much for your reply. This is what I needed!!!