4.5.4 Power Supply Exceptions
This section sums up most exceptions that can occur with the power supply.
Target Voltage Shuts Down
Not reaching the target voltage setting can happen if the target section draws too much current at a given voltage and causes the thermal shutdown safety feature of the MIC5353 regulator to kick in. To avoid this, reduce the current load of the target section.
Target Voltage Setting is Not Reached
The USB input voltage (specified to be 4.4-5.25V) limits the maximum output voltage of the MIC5353 regulator at a given voltage setting and current consumption. If a higher output voltage is needed, use a USB power source with a higher input voltage or use an external voltage supply on the VTG pin.
Target Voltage is Different From Setting
An externally applied voltage to the VTG pin without setting the VOFF pin low can cause this. If the target voltage varies more than 100 mV over/under the voltage setting, the on-board debugger will detect it, and the internal voltage regulator will shut down. To fix this issue, remove the applied voltage from the VTG pin, and the on-board debugger will enable the on-board voltage regulator when the new condition is detected. Note that the PS LED will blink rapidly if the target voltage is below 100 mV of the setting but will ordinarily turn on when higher than 100 mV above it.
No, or Very Low Target Voltage and PS LED is Blinking Rapidly
A full or partial short circuit can cause this and is a particular case of the issue above. Remove it, and the on-board debugger will re-enable the on-board target voltage regulator.
No Target Voltage and PS LED is Lit 1
This situation occurs if the target voltage is set to 0.0V. Set the target voltage to a value within the specified voltage range for the target device to fix this.
No Target Voltage and PS LED is Lit 2
This situation can be the issue when cutting power jumper J200 and/or J201 and setting the target voltage regulator to a value within the specified voltage range for the target device. To fix this, solder a wire/bridge between the pads for J200/J201 or add a jumper on J201 if a pin-header is mounted.
VBUS Output Voltage is Low or Not Present
If the VBUS output voltage is low or missing, the reason is probably a high-current drain on VBUS, and the current limit set by U202 (MIC2008) is tripped and has cut off VBUS completely. Reduce the current consumption on the VBUS pin to fix this issue.