Datasheet

UCC28063

www.ti.com

SLUSAO7 –SEPTEMBER 2011

Open-Loop Protection

If the feedback loop is disconnected from the device, a 100-nA current source internal to the UCC28063 pulls the

VSENSE pin voltage towards ground. When VSENSE falls below 1.20 V, the device becomes disabled. When

disabled, the bias supply current decreases, both gate-drive outputs and COMP are actively pulled low, and a

soft-start condition is initiated. The device is re-enabled when VSENSE rises above 1.25 V. At that time, the gate

drive outputs will begin switching under soft-start PWM control.

If the feedback loop is disconnected from ground, the VSENSE voltage will be pulled high. When VSENSE rises

above the 2nd-level over-voltage protection threshold, both gate drive outputs are shut off and COMP is actively

pulled low. The device is re-enabled when VSENSE falls below the OV-clear threshold. The VSENSE input can

tolerate a limited amount of current into the device under abnormally high input voltage conditions. Refer to the

Absolute Maximum Ratings table near the beginning of this datasheet for details.

VCC Under-Voltage Lock-Out (UVLO) Protection

VCC must rise above the turn-on threshold for the PWM to begin functioning. If VCC drops below the UVLO

threshold during operation, both gate-drive outputs are actively pulled low, COMP is actively pulled low, and a

soft-start condition is triggered. VCC must again rise above the turn-on threshold for the PWM function to restart

in soft-start mode.

Phase-Fail Protection

The UCC28063 detects failure of either of the phases by monitoring the sequence of ZCD pulses. During normal

two-phase operation, if one ZCD input remains idle for longer than approximately 12 ms while the other ZCD

input switches normally, the over-current threshold is reduced and PWMCNTL goes to a high-impedance state,

indicating that the PFC power stage is not operating correctly. During normal single-phase operation (PHB < 0.8

V), phase failure is not monitored. Also on the UCC28063, phase failure is not monitored when COMP is below

approximately 222 mV.

CS-Open, TSET-Open & -Short Protection

In the event that the CS input becomes open-circuited, the UCC28063 detects this condition and will shutdown

the outputs and trigger a full-soft-start condition. In the event that the TSET input becomes either open-circuited

or short-circuited to GND, the UCC28063 detects these conditions and will shutdown the outputs and trigger a

full-soft-start condition. Normal operation will resume (with a soft-start) when the fault clears.

Thermal Shutdown Protection

Overloading of the gate-drive outputs and/or VREF can dissipate excess power within the device which may

raise the internal temperature of the circuits beyond a safe level. Even normal power dissipation can generate

excess heat if the thermal impedance is too high or the ambient temperature is too high. When the UCC28063

detects an internal over-temperature condition it will shutdown the outputs and trigger a full soft-start condition.

When the internal device junction temperature has cooled below the thermal hysteresis temperature, operation

will resume under soft-start control.

AC-Line Brownout and Dropout Protections

See specific discussions for each topic in previous sections (above) of this datasheet.

Product Folder Link(s): UCC28063