LTC3813 Datasheet, PDF (12/32 Pages) Linear Technology – 100V Current Mode Synchronous Step-Up Controller

LTC3813
OPERATION
from DRV_CC when the top MOSFET turns off. In an output
overvoltage condition, where it is possible that the bot-
tom MOSFET will be off for an extended period of time,
an internal timeout guarantees that the bottom MOSFET
is turned on at least once every 25μs for one top MOSFET
on-time period to refresh the bootstrap capacitor.
The bottom driver has an additional feature that helps
minimize the possibility of external MOSFET shoot-thru.
When the top MOSFET turns on, the switch node dV/dt
pulls up the bottom MOSFET’s internal gate through the
Miller capacitance, even when the bottom driver is hold-
ing the gate terminal at ground. If the gate is pulled up
high enough, shoot-thru between the top side and bottom
side MOSFETs can occur. To prevent this from occurring,
the bottom driver return is brought out as a separate pin
(BGRTN) so that a negative supply can be used to reduce
the effect of the Miller pull-up. For example, if a –2V
supply is used on BGRTN, the switch node dV/dt could
pull the gate up 2V before the V_GS of the bottom MOSFET
has more than 0V across it.
IC/Driver Supply Power and Linear Regulators
The LTC3813’s internal control circuitry and top and bottom
MOSFET drivers operate from a supply voltage (INTV_CC,
DRV_CC pins) in the range of 6.2V to 14V. If the input supply
voltage or another available supply is within this voltage
range it can be used to supply IC/driver power. If a supply
in this range is not available, two internal regulators are
available to generate a 10V supply from the input or output.
An internal low dropout regulator is good for voltages up to
15V, and the second, a linear regulator controller, controls
the gate of an external NMOS to generate the 10V supply.
Since the NMOS is external, the user has the flexibility to
choose a BV_DSS as high as necessary.
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