Kingbor Technology Co.,Ltd
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kB3440
OPERATION
Theinputvoltage,VIN,wherethefourswitchregionbegins
is given by:
75%
MAX
BOOST
D
V4 (52.05V)
A ON, B OFF
PWM CD SWITCHES
BOOST REGION
VOUT
1– (150ns• f)
D
MIN
V =
IN
V
V3 (51.65V)
V2 (51.55V)
BOOST
BUCK/BOOST REGION
FOUR SWITCH PWM
D
MAX
BUCK
The point at which the four switch region ends is given by:
VIN = VOUT(1 – D) = VOUT(1 – 150ns • f) V
D ON, C OFF
PWM AB SWITCHES
BUCK REGION
V1 (50.9V)
0%
DUTY
CYCLE
INTERNAL
CONTROL
VOLTAGE, V
Boost Region (VIN < VOUT
)
3440 F02
CI
Switch A is always on and switch B is always off during
thismode.Whentheinternalcontrolvoltage,VCI,isabove
voltage V3, switch pair CD will alternately switch to
provideaboostedoutputvoltage.Thisoperationistypical
to a synchronous boost regulator. The maximum duty
cycle of the converter is limited to 75% typical and is
reached when VCI is above V4.
Figure 2. Switch Control vs Internal Control Voltage, VCI
Buck Region (VIN > VOUT
)
SwitchDisalwaysonandswitchCisalwaysoffduringthis
mode. When the internal control voltage, VCI, is above
voltage V1, output A begins to switch. During the off time
of switch A, synchronous switch B turns on for the
remainder of the time. Switches A and B will alternate
similar to a typical synchronous buck regulator. As the
control voltage increases, the duty cycle of switch A
increasesuntilthemaximumdutycycleoftheconverterin
Burst Mode Operation
Burst Mode operation is when the IC delivers energy to the
output until it is regulated and then goes into a sleep mode
where the outputs are off and the IC is consuming only
40µA. In this mode the output ripple has a variable
frequency component that depends upon load current.
Buck mode reaches DMAX BUCK
_
, given by:
DMAX BUCK = 100 – D4SW
_
%
During the period where the device is delivering energy to
the output, the peak current will be equal to 400mA typical
and the inductor current will terminate at zero current for
each cycle. In this mode the maximum average output
current is given by:
where D4SW = duty cycle % of the four switch range.
D4SW = (150ns • f) • 100 %
where f = operating frequency, Hz.
Beyond this point the “four switch,” or Buck/Boost region
is reached.
0.1• V
VOUT + V
IN
IOUT(MAX)BURST 5
A
IN
Buck/Boost or Four Switch (VIN ~ VOUT
)
Burst Mode operation is user controlled, by driving the
MODE/SYNC pin high to enable and low to disable.
Whentheinternalcontrolvoltage,VCI,isabovevoltageV2,
switch pair AD remain on for duty cycle DMAX_BUCK, and
the switch pair AC begins to phase in. As switch pair AC
phases in, switch pair BD phases out accordingly. When
the VCI voltage reaches the edge of the Buck/Boost range,
at voltage V3, the AC switch pair completely phase out the
The peak efficiency during Burst Mode operation is less
than the peak efficiency during fixed frequency because
the part enters full-time 4-switch mode (when servicing
the output) with discontinuous inductor current as illus-
tratedinFigures3and4.DuringBurstModeoperation,the
control loop is nonlinear and cannot utilize the control
BD pair, and the boost phase begins at duty cycle D4SW
.
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KINGBOR [ KINGBOR TECHNOLOGY CO ]
