LED2001 Smoked with set to 4A output

[Dsun.21]

Dear Support,

I have a design which works fine even drive it full PWM with 0.025 ohm (4A max current). we need to control the backflow current so added a diode on the power supply path.  the schematic is attached. C169 and C170 not installed. it works fine when PWM set to 50% or even 75%. but once set to 100%, the chip will be damaged in 1 or 2 second. I don't think it is a thermal issue, because the same design and layout was used for a long time. something happened that cause the chip entered a nonstable state. any suggestions that can make the design more stable. 

Motor_Enable is a powerful 12V supply.

 

Thank you,

David