LTC3726 Datasheet, PDF (14/16 Pages) Linear Technology – Secondary-Side Synchronous Forward Controller

LTC3726
APPLICATIO S I FOR ATIO
PolyPhase Applications
V_IN+
Figure 4 shows the basic connections for using the
LTC3705/LTC3725 and LTC3726 in PolyPhase applica-
tions. One of the phases is always identified as the “mas-
ter,” while all other phases are “slaves.” For the LTC3705/
LTC3725 (primary side), the master monitors the V_IN
voltage for undervoltage, performs the open-loop start-up
and supplies the initial V_CC voltage for the master and all
slaves. The LTC3705/LTC3725 slaves simply stand by and VIN–
wait for PWM signals from their respective pulse trans-
formers. Since the SS/FLT pins of each master and slave
LTC3705/LTC3725s are interconnected, a FAULT
(overcurrent, etc.) on any one of the phases will perform
a shutdown/restart on all phases together. The LTC3705/
LTC3725 is put into slave mode by omitting the resistor on
FS/IN^–. For the LTC3726, the master performs soft-start
and voltage-loop regulation by driving all slaves to the
same current as the master using the ITH pins. Faults and
shutdowns are communicated via the interconnection of
the RUN/SS pins. The LTC3726 is put into slave mode by
tying the FB pin to V_CC.
V_BIAS
V_OUT+
NDRV
UVLO FB/IN⁺
V_CC
FS/IN^–
SS/FLT
LTC3705/25
(MASTER)
••
V_CC
FS/SYNC
PT⁺
FB/PHASE
PT^–
ITH
RUN/SS
LTC3726
(MASTER)
NDRV
SS/FLT FB/IN⁺
V_CC
UVLO FS/IN^–
LTC3705/25
(SLAVE)
••
V_CC
RUN/SS FS/SYNC
PT⁺
ITH
PT^– FB/PHASE
LTC3726
(SLAVE)
3726 F05
Figure 4. Connections for PolyPhase Operation
3726fb
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