LTC3415 Datasheet, PDF (9/28 Pages) Linear Technology – 7A, PolyPhase Synchronous Step-Down Regulator

LTC3415
OPERATION
Short-Circuit Protection
When the output is shorted to ground, the LTC3415
will drop cycles to allow the inductor time to decay and
prevent the current from running away. Under this fault
condition, the top P-channel power MOSFET turns on for
a minimum on-time and is held off for as long as it takes
for the inductor current to decay to a safe level.
Output Overvoltage
If the LTC3415’s output voltage exceeds the regulation
point by 10%, which is reflected as a V_FB voltage of 0.66V
or above, the LTC3415 will attempt to bring back to regu-
lation by shutting off the top P-channel power MOSFET
and turning on the bottom N-Channel power MOSFET for
as long as needed to lower V_OUT. However, if the reverse
current flowing from V_OUT back through the bottom
N-Channel power MOSFET to PGND is greater than 7A,
the INEGLIM comparator trips and shuts off the bottom
N-Channel power MOSFET to protect it from being de-
stroyed. This scenario can happen when the LTC3415 tries
to start into a pre-charged load, which could trigger the
overvoltage comparator during the time the LTC3415’s
internal reference is powering up. As a result, the bottom
switch turns on until the amount of reverse current trips
the INEGLIM comparator threshold.
Multiphase Operation
For output loads that demand more than 7A of current,
multiple LTC3415s can be cascaded to run out of phase to
provide more output current without increasing input and
output voltage ripple. The CLKIN pin allows the LTC3415
to synchronize to an external clock (between 0.75MHz and
2.25MHz) and the internal phase-locked-loop allows the
LTC3415 to lock onto CLKIN’s phase as well. The CLKOUT
signal can be connected to the CLKIN pin of the following
LTC3415 stage to line up both the frequency and the phase
of the entire system. Tying the PHMODE pin to SV_IN, SGND,
or SV_IN/2 generates a phase difference (between CLKIN
and CLKOUT) of 180 degrees, 120 degrees, or 90 degrees
respectively, which corresponds to 2-phase, 3-phase, or
4-phase operation. A total of 12 phases can be cascaded
to run simultaneously out of phase with respect to each
+120
0
+120
CLKIN CLKOUT
180
CLKIN CLKOUT
S_VIN PHMODE
S_VIN PHMODE
PHASE 1
PHASE 2
3415 F02a
Figure 2a. 2-Phase Operation
0
+120
CLKIN CLKOUT
120
+120
CLKIN CLKOUT
240
CLKIN CLKOUT
PHMODE
PHASE 1
PHMODE
PHMODE
PHASE 2
Figure 2b. 3-Phase Operation
PHASE 3
3415 F02b
0
+90
CLKIN CLKOUT
90
+90
CLKIN CLKOUT
180
+90
CLKIN CLKOUT
270
CLKIN CLKOUT
SV_IN
PHMODE
2
PHASE 1
SV_IN
PHMODE
2
PHASE 2
SV_{IN PHMODE}
2
PHASE 3
Figure 2c. 4-Phase Operation
SV_IN
2
PHMODE
PHASE 4
3415 F02c
3415fa
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