TPS2412: How do I verify Oring FET number

Hello Alan,

I believe the question is on the number MOSFETs that can used in parallel and the ability of TPS2412 to drive them for ORing application?

Could you confirm this.

Regards,
Kari.

Hi Kari,

     yes, you're correct.

Hello Alan,

Capabiliy of driving MOSFETs in parallel depends gate drive charging current (>250uA) and gate turn off pull down current >1.25A.

During startup up, gate charging current of >250uA charges gate capacitance (Ciss or Qg) of MOSFET. Before the MOSFET is turned ON, body diode of the MOSFET conducts for small time. And this current should not exceed the maximum source current of the N-Channel MOSFET used. Duration of the turn on time is calculated by I_Turn_ON = Ciss_total * (VIN+Vth_MOSFET) / 250uA, where VIN is input voltage and Vth_MOSFET is gate threshold voltage of the MOSFET, Ciss_total is total gate capacitance of MOSFETs in parallel.

Turn off capability is determined by its ability to pull down the gate voltage and its dependent on the gate capacitance of the all the MOSFETs in parallel.

Maximum gate capacitance allowed (total gate capacitance) Ciss_total = 1.25 *  7.5 / (11.5V-Vth_MOSFET) (in us).

Regards,

Kari.

Hi

Correction, Ciss_total is in uF and not in us.

Regards,

Kari.