LT3755-1 LINER [Linear Technology], LT3755-1 Datasheet - Page 13

• Manufacturer Part Number: LT3755-1
• Description: 60V 4-Switch Synchronous
• Manufacturer: LINER [Linear Technology]

OPERATION
Buck Region (V
Switch M4 is always on and switch M3 is always off during
this mode. At the start of every cycle, synchronous switch
M2 is turned on first. Inductor current is sensed when
synchronous switch M2 is turned on. After the sensed
inductor current falls below the reference voltage, which
is proportional to VC, synchronous switch M2 is turned off
and switch M1 is turned on for the remainder of the cycle.
Switches M1 and M2 will alternate, behaving like a typical
synchronous buck regulator. The duty cycle of switch M1
increases until the maximum duty cycle of the converter
in buck operation reaches D
D
MAX(BUCK,TG1)
IN
> V
= 100% – D
OUT
)
MAX(BUCK, TG1)
(BUCK-BOOST)
M2 + M4
M1+ M3
M1 + M4
M1 + M4
M2 + M4
Figure 5. Buck-Boost Operation (V
Figure 4. Buck-Boost Operation (V
M1 + M3
M1 + M4
, given by:
M2 + M4
Figure 3. Buck Operation (V
M1 + M4
M1 + M4
M2 + M4
M1+ M3
M1 + M4
M1 + M4
M2 + M4
M1 + M3
M1 + M4
M2 + M4
M1 + M4
where D
switch range:
Figure 3 shows typical buck operation waveforms. If V
approaches V
Buck-Boost (V
When V
operation. Figure 4 and Figure 5 show typical waveforms
in this mode. Every cycle the controller turns on switches
M2 and M4, then M1 and M4 are turned on until 180° later
when switches M1 and M3 turn on, and then switches
M1 and M4 are turned on for the remainder of the cycle.
D
M1 + M4
(BUCK-BOOST)
IN
M2 + M4
IN
M1+ M3
(BUCK-BOOST)
> V
IN
IN
M1 + M4
is close to V
M1 + M4
≥ V
OUT
≤ V
M2 + M4
OUT
OUT
OUT
)
IN
M1 + M4
M1 + M3
M2 + M4
M1 + M4
)
)
~ V
= 8%
, the buck-boost region is reached.
OUT
M1 + M4
3791 F03
is the duty cycle of the buck-boost
OUT
3791 F05
3791 F04
)
, the controller is in buck-boost
LT3791
13
3791f
IN