Description: Dear Sir,
My customer is using our S12ZM in their pump motor controller project(motor type is DC brush motor, so only 2 high sides and 2 low sides are used) and they meet issue of PWM dead-time settings and GDU external circuit design:
1. the dead-time setting of low side is correct while it’s much more shorter than the setting on high side: when set 1 us as the dead-time for both HS and LS, they measure about 0.4us dead-time on HS and about 1.05us on LS, is it normal, why it will has such huge difference on HS?
2. the customer adds a 33Ω resistor between S12ZVM GDU HSx/LSx and gate input pin of external power MOSFET, and also add a RC filter(R=470K and C=10nf) between gate and source of every power MOSFET for protection, which is necessary for their before products(use independent pre-driver, not integrated GDU as our S12ZVM): customer GDU external circuit is as below:
customer tests to find the 33 Ω serial resistor on MOSFET gate input will change S12ZVM GDU high side output HGx signal’s falling slope, make it become slow compare with LSx or without the resistor, while its rising slope is OK, also no such influence on LSx.(as below photo, set deadtime = 2us, the HSx is falling and LS is rising):
After remove the 33 Ω serial resistor, the HGx signal’s falling slope becomes normal.
How does this happen? Is it necessary to add the 33Ω serial resistor between S12ZVM GDU HSx/LSx and gate input pin of external power MOSFET, and the RC filter(R=470K and C=10nf) between gate and source of every power MOSFET for protection in S12ZM GDU application?
PS: I reviewed all our S12ZVM demo-boards and reference design, there is only a 0Ω serial resistor between S12ZVM GDU HSx/LSx and gate input pin of external power MOSFET and no the RC filter circuit between gate and source of every power MOSFET. attached schematic of S12ZVML_MINIBRD as below for your reference: