The UCC2895x-Q1 controllers offer
many operational modes. These modes are described in detail in Section 6.3.
- Current mode1. The UCC2895x-Q1 controller operates in current mode control
when the RSUM pin is connected to GND through a resistor (RSUM) . The
resistor sets the amount of slope compensation.
- Voltage mode1. The controller operates in voltage mode control when the RSUM pin is
connected to VREF through a resistor (RSUM). The chosen resistor
value gives the correct amount of slope compensation for operation in current
limit mode (cycle-by-cycle current limit).
- DCM mode. The controller enters DCM mode when the
signal at the CS pin falls below the level set by the resistor at the DCM pin.
The SR drives (OUTE and OUTF) turn off and secondary rectification occurs
through the body diodes of the SRs.
- Burst mode. The controllers enter burst mode when
the pulse width demanded by the feedback signal falls below the width set by the
resistor at the TMIN pin.
- Leader mode. This is the default operation mode
of the controller and is used when there is only one UCC2895x-Q1
controller in the system. Connect the timing resistor (RT) from the
RT pin to VREF. In a system with more than one UCC2895x-Q1
controller, configure one as the leader and the others as followers1.
- Follower mode. The follower controller operates
with a 90° phase shift relative to the leader (providing their SYNC pins are
tied together). Connect the timing resistor (RT) from the RT pin to
GND and connect an 825kΩ ±5% resistor from the SS/EN pin to GND1.
- Synchronized mode. When a UCC2895x-Q1 controller is configured as a follower, its SYNC pin is used as an input. The
follower synchronizes its internal oscillator at 90° to the signal at its SYNC
pin. The application note, Synchronizing Three or More
UCC28950 Phase-Shifted, Full-Bridge Controllers, discusses
how multiple follower controllers may be synchronized to a single leader
oscillator.
- Hiccup mode. This mode provides overload
protection to the power circuit. The UCC2895x-Q1 controller stops
switching after a certain time in current limit. It starts again (soft-start)
after a delay time. The user can control the time spent in current limit before
switching is stopped and the delay time before the soft start happens.
- Current-limit mode. The UCC2895x-Q1c
ontroller provides cycle-by-cycle current limiting when the signal at the CS pin
reaches 2V.
- Latch-off mode. Connect a resistor between the SS
pin and VREF. The UCC2895x-Q1 controller then latches off when
the controller enterscurrent-limit mode. (1)