Datasheet
UCC28700, UCC28701
UCC28702, UCC28703
www.ti.com
SLUSB41 – JULY 2012
Fault Protection
There is comprehensive fault protection incorporated into the UCC28700. Protection functions include:
• Output over voltage
• Input under voltage
• Internal over temperature
• Primary over-current fault
• CS pin fault
• VS pin fault
A UVLO reset and restart sequence applies for all fault protection events.
The output over-voltage function is determined by the voltage feedback on the VS pin. If the voltage sample on
VS exceeds 115% of the nominal V
OUT
, the device stops switching and keeps the internal circuitry enabled to
discharge the VDD capacitor to the UVLO turn-off threshold. After that, the device returns to the start state and a
start-up sequence ensues.
The UCC28700 always operates with cycle-by-cycle primary peak current control. The normal operating range of
the CS pin is 0.75 V to 0.25 V. There is additional protection if the CS pin reaches 1.5 V. This results in a UVLO
reset and restart sequence. There is no leading-edge blanking on the 1.5-V threshold on CS.
The line input run and stop thresholds are determined by current information at the VS pin during the MOSFET
on-time. While the VS pin is clamped close to GND during the MOSFET on-time, the current through R
S1
is
monitored to determine a sample of the bulk capacitor voltage. A wide separation of run and stop thresholds
allows clean start-up and shut-down of the power supply with the line voltage. The run current threshold is 220
µA and the stop current threshold is 80 µA.
The internal over-temperature protection threshold is 165°C. If the junction temperature reaches this threshold
the device initiates a UVLO reset cycle. If the temperature is still high at the end of the UVLO cycle, the
protection cycle repeats.
Protection is included in the event of component failures on the VS pin. If complete loss of feedback information
on the VS pin occurs, the controller stops switching and restarts.
Copyright © 2012, Texas Instruments Incorporated Submit Documentation Feedback 17
Product Folder Link(s): UCC28700, UCC28701 UCC28702, UCC28703