Custom LED Driver (A6211, XHP70.2) — Switching but No Regulation

Build/Make
1

Hi All, I built a custom LED driver based on the BlueRobotics reference design to drive a Cree XHP70.2 (12 V version).

  • Input: ~16.5 V

  • Target regulated output: ~12 V

  • PWM input: 3.3 V from ATTiny45 MCU

  • Driver IC: Allegro A6211

What we found so far:

  • Fixed: Freewheeling diode D1 was assembled reversed → short on SW node and destroyed the diode on the first boards.

  • After fixing D1 polarity:

    • SW node is now switching

    • Output voltage is stuck at 15.6 V (almost equal to input voltage) → completely unregulated

    • CS pin reads 0 V on every board (regulation loop appears dead)

    • LED has never illuminated

Additional observations:

  • TON pin: 1.2 V

  • EN pin: 2.8–2.9 V (instead of expected ~3.3 V)

  • BOOT pin: ~19 V (seems normal for bootstrap)

I also tried powering the XHP70.2 directly with a 12 V / 1.5 A bench supply — still no light at all.

I’ve attached the schematic and PCB layout for review. The LED footprint was custom designed from the Cree datasheet. I’m especially concerned about the LED pads and the RSENSE / CS trace routing.

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Questions:

  1. Has anyone seen the CS pin stuck at 0 V on the A6211? Any known layout pitfalls with RSENSE or CS trace?

  2. Any experience with completely unregulated output (Vout ≈ Vin) even though SW is switching?

  3. Does TON pin reading 1.2 V (VIN ~16.5 V) point to latch-up or a protection mode?

  4. What is the minimum current/voltage for a basic sanity check on a Cree XHP70.2?

Any help, scope-shot suggestions, or layout feedback would be really appreciated. Happy to share more measurements or design files.

Thanks in Advance

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Please check the pad layout and connections made for 12V configuration of xhp70.2 as per the datasheet