Tool/software:
Hello,
I’m using a DRV8311H to drive a three‑phase BLDC. My problem is that the CP pin never charges—it sits at about VM–0.4 V no matter what I try, and nFAULT stays low. Here’s what I’ve done so far:
-
VM rail
– 12 V, well above UVLO.
– VM is stable before toggling nSLEEP. -
nSLEEP/nFAULT
– I hold nSLEEP high after VM comes up.
– nFAULT reads as 0 continuously.
- I’ve tried toggling nSLEEP low → high -
Flying cap
– YAGEO CC0603KRX7R9BB104 (100 nF, 50 V, X7R).
– I placed it between the CP pad and VM pad in 0603 footprint.
– Caps tested by swap/hot‑air — no visible cracks. -
Probe
– CP never rises above ~11.6 V (i.e. VM–0.4 V).
What I’ve ruled out
-
No shorts or other loads on CP.
-
nSLEEP timing is correct.
What I need help with
-
Is there any hidden requirement for the flying cap (ESR, placement, orientation)?
-
Could back‑powering the LDO via AVDD affect the pump start?
-
Other layout or schematic pitfalls?
Thanks in advance for any pointers. I’ve attached my schematic for reference.
