LTC3812-5_15 Datasheet, PDF (8/34 Pages) Linear Technology – 60V Current Mode Synchronous Switching Regulator Controller

LTC3812-5
TYPICAL PERFORMANCE CHARACTERISTICS
RUN/SS Pull-Up Current
vs Temperature
3
RUN/SS = 0V
2
1
0
–50 –25
0 25 50 75
TEMPERATURE (°C)
100 125
38125 G27
Shutdown Threshold
vs Temperature
2.2
2.0
1.8
1.6
1.4
1.2
1.0
0.8
0.6
–50 –25
0 25 50 75
TEMPERATURE (°C)
100 125
38125 G28
PIN FUNCTIONS
I_ON (Pin 1): On-Time Current Input. Tie a resistor from V_IN
to this pin to set the one-shot timer current and thereby
set the switching frequency.
V_RNG (Pin 2): Sense Voltage Limit Set. The voltage at this
pin sets the nominal sense voltage at maximum output
current and can be set from 0.5V to 2V by a resistive
divider from INTV_CC. The nominal sense voltage defaults
to 95mV when this pin is tied to ground, and 215mV when
tied to INTV_CC.
PGOOD (Pin 3): Power Good Output. Open-drain logic
output that is pulled to ground when the output voltage
is not between ±10% of the regulation point. The output
voltage must be out of regulation for at least 120μs before
the power good output is pulled to ground.
FCB (Pin 4): Pulse-Skipping Mode Enable Pin. This pin
provides pulse-skipping mode enable/disable control.
Pulling this pin below 0.8V disables pulse-skipping mode
operation and forces continuous operation. Pulling this pin
above 0.8V enables pulse-skipping mode operation. This
pin can also be connected to a feedback resistor divider
from a secondary winding on the inductor to regulate a
second output voltage.
I_TH (Pin 5): Error Amplifier Compensation Point and Cur-
rent Control Threshold. The current comparator threshold
increases with control voltage. The voltage ranges from
0V to 2.6V with 1.2V corresponding to zero sense voltage
(zero current).
V_FB (Pin 6): Feedback Input. Connect V_FB through a resistor
divider network to V_OUT to set the output voltage.
RUN/SS (Pin 7): RUN/Soft-Start Input. For soft-start, a
capacitor to ground at this pin sets the ramp rate of the
output voltage (approximately 0.6s/μF). Pulling this pin
below 1.5V will shut down the LTC3812-5, turn off both of
the external MOSFET switches and reduce the quiescent
supply current to 224μA.
SGND (Pin 8): Signal Ground. All small-signal components
should connect to this ground and eventually connect to
PGND at one point.
NDRV (Pin 9): Drive Output for External Pass Device of
the Linear Regulator for INTV_CC. Connect to the gate of
an external NMOS pass device and a pull-up resistor to
the input voltage V_IN.
38125fc
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