# Why L6743D MOSFET driver is not working properly?

I've started to build a brushless driver by using some Power MOSFETs and some MOSFET drivers, in order to drive the Power MOSFETs.

I have connected the chips as shown in the application circuit (page 3) in the datasheet of the L6743D MOSFET driver, in order to drive my couple of N-MOSFET, but I noticed that nothing worked as it should.

After that, I decided to check if the MOSFET Driver (L6743D) is working as it should. Therefore I have powered up the L6743D with 12 V Vcc, set High the EN pin (5 V of the micro) and set the PWM input from my micro (Arduino).

At this point I noticed that the UGATE pin keeps staying HIGH (constant at Vcc = 12 V), while the LGATE is following the PWM signal's shape.

According to the datasheet listed above (page 8), the UGATE pin should be the opposite of the LGATE pin. Hence I should have something similar to my PWM signal given as input and both the signals should turn on/off the Power MOSFETs.

This is not happening and I really don't understand what I'm doing wrong.

Could you help me, please? Am I missing something about the usage of the L6743D MOSFET Driver?

EDIT

Here you are my circuit, consider the couple of N-MOSFETs into the same package.

When I turn on the power supplier and limit the current to 200mA, the power supplier shows me that there is a CC. I have also tried to set the limit higher without any success.

Hope this is helpful to understand my issue.

• Post a picture of your circuit construction. – pgvoorhees Jul 5 '16 at 15:03
• When you did your test, where did you connect the PHASE pin? The High-Side driver output UGATE uses PHASE as its 'low' output value, so you can't leave it floating. – brhans Jul 5 '16 at 15:15
• What is your bootstrap capacitor and resistor value and PWM frequency? – John Birckhead Jul 5 '16 at 15:49
• I've posted the circuit schema above. The frequency of my PWM is around 500 Hz, but I can take it to 10 KHz if needed. – starScream Jul 5 '16 at 19:04
• To expand on @brhans comment: When you measured the voltage on UGATE, did you measure it with respect to GND? or with respect to PHASE? Were the MosFETs attached? You need to measure UGATE with respect to PHASE, and you need the lower MosFET to turn on in order to charge the bootstrap capacitor. – Mark Jul 5 '16 at 19:48

• Hence my circuit schema should be fine, am I correct? Furthermore, what do you mean with PWM LOW for the motor phase LOW, do I have just to set it to 0 V? And by saing PWM input for high and enable to turn it on and off do you mean that I should apply the PWM signal to the PWM input pin as constant, and turn the driver ON and OFF by using the ENABLE pin? – starScream Jul 14 '16 at 20:53