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LTC4440 TG not responsing

Hi to all,

I am trying to build a DC/DC step down converter. I used LTC4440 Gate Driver IC for switching a N Channel Power Mosfet as a high side switch. I used 555 Timer Circuit to arrange the PWM as Vpp = 12V to Pwm(in) of the driver IC pin as suggested in the datasheet. The PWM circuit works as expected but my LTC Driver is not responding somehow. I was suspicious of the value of the Bootstrap Capacitor and did a little research to calculate it accurately but no change received in the IC. I share the schematics of the gate driver below. Any help is appreciated. Thanks.

Q1 : NTB60N06 60V, 60A Power Mosfet (D2Pak)

D1 : 1N4007

C3: 16V - 0.22uF Ceramic Cap

R1: 2512, 1.5W, %1, 15R

 

  • If the Main Supply (VVCC) or the Bootstrapped Supply (VBOOST - VTS) is below the undervoltage lockout threshold, there is no output.  A diode from VCC to the BOOST pin (or in your case, D1) provides a path to initially (and periodically) charge the BOOST-TS capacitor (C3). This also requires an output load (TS to pull to ground). I would suggest modeling your circuit (including input frequency and load) in LTspice. The LTC7001 is very similar but contains a charge pump to allow the output to stay high for long periods of time but has similar frequency restrictions.

  • Hey Kurk,

    Thank you for your time, but i solved the problem already just forgot to keep here updated. Anyways the problem is not the schematics or the supply voltage. Its because the PCB design. Somehow i didn't care much about positioning the bootstrap capacitor but it should' ve been really close to the IC. I found the issue while reviewing the datasheet. It mentioned as close as possible and there was no recommended pcb layout as a reference as well. However, i am happy of the result since the converter works as expected.

    Regards,

    Kakaoo