LTC3810EG LINER [Linear Technology], LTC3810EG Datasheet - Page 13

• Manufacturer Part Number: LTC3810EG
• Description: 100V Current Mode Synchronous Switching Regulator Controller
• Manufacturer: LINER [Linear Technology]

OPERATION
Fault Monitoring/Protection
Constant on-time current mode architecture provides ac-
curate cycle-by-cycle current limit protection—a feature
that is very important for protecting the high voltage power
supply from output short circuits. The cycle-by-cycle cur-
rent monitor guarantees that the inductor current will never
exceed the value programmed on the V
Foldback current limiting provides further protection if the
output is shorted to ground. As V
current threshold voltage I
to 1V. This reduces the inductor valley current level to
one-sixth of its maximum value as V
Foldback current limiting is disabled at start-up.
Overvoltage and undervoltage comparators OV and UV
pull the PGOOD output low if the output feedback voltage
exits a ±10% window around the regulation point after the
internal 120μs power bad mask timer expires. Furthermore,
in an overvoltage condition, M1 is turned off and M2 is
turned on immediately and held on until the overvoltage
condition clears.
The LTC3810 provides two undervoltage lockout com-
parators—one for the INTV
the input supply V
guarantee that the MOSFETs have suffi cient gate drive volt-
age before turning on. The V
0.8V with 10% hysteresis which allows programming the
V
nected to V
UV threshold, the LTC3810 is shut down and the drivers
are turned off.
Strong Gate Drivers
The LTC3810 contains very low impedance drivers capable
of supplying amps of current to slew large MOSFET gates
quickly. This minimizes transition losses and allows paral-
leling MOSFETs for higher current applications. A 100V
fl oating high side driver drives the top side MOSFET and
a low side driver drives the bottom side MOSFET (see
Figure 3). The bottom side driver is supplied directly
from the DRV
from fl oating bootstrap capacitor, C
recharged during each off cycle through an external diode
from DRV
IN
threshold with the appropriate resistor divider con-
CC
IN
. If either comparator inputs are under the
when the top MOSFET turns off. In pulse
CC
pin. The top MOSFET drivers are biased
IN
. The INTV
THB
CC
IN
is pulled down and clamped
/DRV
UV threshold (UVIN pin) is
CC
UV threshold is 6.2V to
FB
CC
B
drops, the buffered
, which normally is
supply and one for
FB
RNG
approaches 0V.
pin.
skip mode operation, where it is possible that the bottom
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 on-time period
to refresh the bootstrap capacitor.
The bottom driver has an additional feature that helps
minimize the possibility of external MOSFET shoot-through.
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 holding
the gate terminal at ground. If the gate is pulled up high
enough, shoot-through 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 sup-
ply is used on BGRTN, the switch node dV/dt could pull
the gate up 2V before the V
more than 0V across it.
IC/Driver Supply Power
The LTC3810’s internal control circuitry and top and bottom
MOSFET drivers operate from a supply voltage (INTV
DRV
has two integrated linear regulator controllers to easily
generate this IC/driver supply from either the high voltage
input or from the output voltage. For best effi ciency the
supply is derived from the input voltage during start-up
and then derived from the lower voltage output as soon
as the output is higher than 6.7V. Alternatively, the supply
can be derived from the input continuously if the output
Figure 3. Floating TG Driver Supply and Negative BG Return
LTC3810
CC
pins) in the range of 6.2V to 14V. The LTC3810
0V TO –5V
DRV
BGRTN
DRV
CC
CC
BOOST
SW
BG
TG
GS
D
C
B
of the bottom MOSFET has
B
V
IN
M1
M2
LTC3810
L
3810 F03
+
+
13
C
C
V
IN
OUT
OUT
3810fb
CC
,