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# LM25148-Q1: Max MOSFET gate charge at 2.1 MHz

Part Number: LM25148-Q1

Hi team,

my customer is looking into LM25148-Q1 in single phase configuration to regulate a 3V3 rail from a 12 V car battery. Targeted output current is ~16 A.

The question cam up:

What is the max power MOSFETs gate charge the controller can drive at 2.1 MHz switching frequency.

Kind regards

Dierk Bronner

• Hi Dierk,

Ivcc = Qg*Fsw, so the theoretical Qg(max) is Ivcc(max)/Fsw.

In practice, 16A is a bit high at 2.1MHz from a thermal standpoint. We have a 15A design that I will send you ask an example, but the recommendation is to go to 440kHz.

Regards,

Tim

• Hello Deirk,

You will need to look at the VCC current limit.  This VCC regulator supplies power to the gate drive circuitries.  It is capable of delivering 200mA typ.  You will need to calculate the total currents required to drive the HS and LS MOSFETs.  This is calculated by looking up the total gate charge of each MOSFET selected.  Add total gate charge for the HS and LS MOSFET.  The required current from the VCC regulator is Qg(total)*Fsw = I_gate_drive.  I_gate_drive needs to be less than the min current limit of the VCC regulator of 110mA as detailed in section 8.3.2 in the DS.  You can always supply a VCC with an external supply using VCCX, if you need more current and want to minimize power dissipation in the device.

Hope this helps.

David.