A TON_MAX fault was detected because the VSENSE voltage did not reach the VOUT_UV_FAULT_LIMIT before the TON_MAX_FAULT_LIMIT. 

Possible Causes:

• Output is shorted, preventing Vout ramp.
• TON_MAX_FAULT_LIMIT set shorter than Vout’s ramp up time
  • Large soft start cap
• VOUT_UV_FAULT_LIMIT set too high.
• Regulator feedback resistor value(s) incorrect or assembly issue.
• VOUT_EN pin has no pullup resistor or power supply enable/RUN pin not pulled high.
• VOEN not physically connected to the power supply enable/RUN pin (failed or missing connection)
  
• Power supply's input is not enabled, or too weak for regulation
  • If its input is sequenced, enable it before this channel

Remedies and Workarounds

Here are some experiments you can try to narrow things down:

• Increase TON_MAX_LIMIT to see if the problem goes away
• Set TON_MAX_FAULT_RESPOSNE to 'ignore' to see if the output voltage comes up
• Lower the VOUT_UV_FAULT_LIMIT and see if the problem goes away

Other Debugging Tips

There are a number of scenarios which can create a TON_MAX_FAULT.  If you have an oscilloscope, perhaps the fastest way to insight is to:

• Trigger the scope on the falling edge of the ALERTB signal, and 
• Look at the VOEN and VSENSE at the pins of the IC, and 
• VIN for the offending channel.  

The ALERTB signal will be pulled low by the IC at the time of the fault, indicating the time of the fault.