I am building a BLDC drive circuit for a 24V/60W BLDC motor. I chose SI4564DY(P+N) and FAN3278 to realize it as shown below (I only include A+ and A-, B and C are exactly the same). The FB indicated at SI4564 output was short-circuited on the PCB using solder during the test.
When I tested the circuit using 12V as VCC to drive the motor at low speed, SI4564 became hot very quickly even when the current from DC power supply showed less than 200mA. I checked the gate signals at FAN3278 input (A+ is PWM with 15% duty cycle, A- is full-on) and SI4564 gate input signals AH and AL
I noticed that there are rich ripples at SI4564 AH and AL and the minimum voltage at AH is about 2.5V rather than 0V. So my questions are
- Does the circuit has any problem? If yes, would anyone please suggest how to change it.
- What could be the reason the SI4564 became so hot under such small current?
- What could have caused so many rippled on AH and AL? Could it cause any damage to the chip?
- Why are there voltage offset (~2.5V) in AH?
This is my first design and I really appreciate anyone's help. Thanks in advance.
Since I can only use two links at this moment, I have to combine several pictures into one. So, to reply to Bruce Abbott for the current issue, I added another picture, marked as Fig 2-4. Fig2-4 is the current sampled by a 0.1 ohm resistor at the lower arm of the bridge to sample motor phase current, and the peak value is 0.23V, which means motor phase current is 2.3A.