LM5060-Q1: Showing unwanted several ringing currents during power insertion..

Hi Ernest,

Thanks for reaching out!

We see these ringing when the FET has high trans conductance. Can you add capacitance (10nF to 22nF) between GATE to GND and check.

Best Regards,

Rakesh

Hi Rakesh,

Thank you for your reply. I will deliver this information to the customer and back to you with their feedback.

Thank you.

Ernest

sure Ernest

Hi Rakesh,

Customer is not tested by adding gate to gnd capacitor yet, but they sent another waveform that showed abnormal results.

I guess excessive overshoot on VGS at the startup makes the device abnormal, but I would like to confirm and issue and want to know the resolution of this issue.

Can you give your insight?

<Waveforms>

- CH1 (Yellow) : VIN
- CH2 (Green) : VGS
- CH3 (Magenta) : VTIMER
- CH4 (Cyan) : nPGD

Best Regards,
Ernest Cho

Hi Ernest,

The overshoot on VGS is due to Cgd coupling from the Vin side.

What is the slew-rate of input voltage ? Is there any input capacitance ?

How VGS is measured ?

Best Regards,

Rakesh

Rakesh,

Sorry, CH2 is VGATE (Gate to GND), it is typo.
(FYI, Once I discussed them regarding their "VDS" voltage waveform, at that time they measured it with differential probe).

They have input capacitance, but this time they used power supply with toggle switch because they encountered first issue above due to the VCC slow ramp up.

I will let them test it again sooner.

Thank you.
Ernest

ok Ernest

Hi Rakesh,

Customer send me the waveforms. They tested by using new pcb with and without the gate capacitor(10nF) and for both slow and fast ramping the supply power..

<schematic and measured points>

CH1 : VIN, 20V/div, CH2 : Vgate, 10V/div, CH3 : Vtimer : 10V/div, CH4 : VnPGD : 1V/div

<Power supply slow ramp up waveform> 

- With gate cap (5ms /div?)

- without gate cap (5ms / div?)

<Power supply slow ramp up waveform> 

- With gate cap (5ms /div)

- Without gate cap (10ms/div)

Sorry for poor resolution. But please see the waveform above and give your idea.

Best Regards, 
Ernest

Hi Ernest,

We have seen similar behaviors in few cases when the FET has high transconductance. I will share those E2E links on Monday 

What is the value of transconductanc for this FET?

Best regards,

Rakesh

Hi Rakesh,

Their FET P/N is IAUC60N06S5N074 (Infineon).
It is not specified the transconductance value in the datasheet, but please refer to the Id vs Vgs graph.

Thank you.

 Hi Ernest,

The transconductance looks in the order of 70 for this MOSFET. we can choose FET with gfs <20 or further slow down the turn-on process by increasing the capacitance on GATE to GND to 22nF or 33nF

Also, make input voltage stable by adding input capacitance (say 10uF)

https://e2e.ti.com/support/power-management-group/power-management/f/power-management-forum/752529/lm5060-unable-to-load-high-capacitive-load-motor-controller-inverter---main-failure

Best Regards,

Rakesh