Datasheet

K =
TL
R
TSET
133kW
´ 4.0
ms
V
(5)
T =
MIN
R
TSET
133kW
´ 2.2ms;MinimumSwitchingPeriod
(6)
Natural Interleaving
Phase Management
UCC28061
www.ti.com .............................................................................................................................................................. SLUS837A – JUNE 2008 – REVISED JULY 2009
The on-time factors (K
TH
, K
THS
, K
TL
, K
TLS
) and the minimum switching period T
MIN
are proportional to the time
setting resistor R
TSET
, the resistor from the TSET pin to ground, and they can be calculated by Equation 5
through Equation 6 :
The proper value of R
TSET
results in the clamped maximum on-time, T
ON(max)
, required by the converter operating
at the minimum input line and maximum load.
Under normal operating conditions, the UCC28061 regulates the relative phasing of the channel A and channel B
inductor currents to be very close to 180 ° , minimizing the ripple currents seen at the line source and output
capacitor. The phase control function differentially modulates the on-times of the A and B channels based on the
phase and frequency relationship. This natural interleaving method allows the converter to achieve 180 ° phase
shift and transition mode operation for both phases without the requirements on boost inductor tolerance. As a
result, the current sharing of the A and B channels are proportional to the inductor tolerance. The best current
sharing is achieved when both inductors are exactly the same value.
At light load, it can improve efficiency to shut down one phase. Although conduction losses increase in
one-phase operation, switching losses decrease. At certain power levels, the reduction of switching losses is
greater than the increase in conduction losses. Turning off one phase at light load is especially valuable for
meeting light-load efficient standards.
To operate in two-phase (normal) mode, pull PHB high or connect PHB to VREF. To operate in one-phase
mode, connect PHB to ground.
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