LM25069: Upper limit of gate capacitor

Yuto Sakai

Part Number: LM25069
Other Parts Discussed in Thread: LM5069

Hi,

Is there an upper limit value for the capacitor connected to the gate pin?
Our customer connects 1μF capacitor.
Also, 1 kΩ is connected in series with the gate of the MOSFET.
is there any ploblem?

Best regards,
Yuto Sakai

over 6 years ago

0 Rakesh over 6 years ago

TI__Guru** 105361 points

Hi Yuto Sakai,

What is driving the need for such large capacitor at the gate pin. Instead of 1kohm series resistor, use the following configuration.

Best Regards,

Rakesh

0 Yuto Sakai over 6 years ago in reply to Rakesh

Mastermind 6100 points

Hi Rakesh-san,

Thank you for your reply.
It is for slew rate adjustment and prevention of inrush current.
The customer's circuit is as follows. is there a problem?

Best regards,
Yuto Sakai

0 Rakesh over 6 years ago in reply to Yuto Sakai

TI__Guru** 105361 points

Hi Yuto Sakai,

max. cap allowed on GATE pin directly is 10nF. with dv/dt circuit, we can use Cdv/dt upto 220nF.
Understood about your inrush current management need. what is the load capacitance and target Vout slew-rate?

Best Regards,
Rakesh

0 Yuto Sakai over 6 years ago in reply to Rakesh

Mastermind 6100 points

Hi Rakesh-san,

Thank you for your reply.
I'll comfirm the load capacitor and slew rate target for customers.
If the capacitor on the GATE pin is too large, is there any concern?

Best regards,
Yuto Sakai

0 Rakesh over 6 years ago in reply to Yuto Sakai

TI__Guru** 105361 points

Hi Yuto Sakai,

The large capacitor at GATE will not discharge fast enough during short circuit fault and causes stress on the FET. The dvdt circuit shown in LM5069 schematic will help to discharge the GATE cap quickly.

Best Regards,
Rakesh

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LM25069: Upper limit of gate capacitor