LTC3711 Datasheet, PDF (7/24 Pages) Linear Technology – 5-Bit Adjustable, Wide Operating Range, No RSENSE

LTC3711
PI FU CTIO S
VID0-VID4 (Pins 23, 24, 1, 12, 13): VID Digital Inputs.
The voltage identification (VID) code sets the internal
feedback resistor divider ratio for different output voltages
as shown in Table 1. If unconnected, the pins are pulled
high by internal 2.5µA current sources.
RUN/SS (Pin 2): Run Control and Soft-Start Input. A
capacitor to ground at this pin sets the ramp time to full
output current (approximately 3s/µF) and the time delay
for overcurrent latchoff (see Applications Information).
Forcing this pin below 0.8V shuts down the device.
V_ON (Pin 3): On-Time Voltage Input. Voltage trip point for
the on-time comparator. Tying this pin to the output
voltage makes the on-time proportional to V_OUT. The
comparator input defaults to 0.7V when the pin is grounded,
2.4V when the pin is tied to INTV_CC.
PGOOD (Pin 4): Power Good Output. Open drain logic
output that is pulled to ground when the output voltage is
not within ±7.5% of the regulation point.
V_RNG (Pin 5): Sense Voltage Range Input. The voltage at
this pin is ten times the nominal sense voltage at maxi-
mum output current and can be set from 0.5V to 2V by a
resistive divider from INTV_CC. The nominal sense voltage
defaults to 70mV when this pin is tied to ground, 140mV
when tied to INTV_CC.
FCB (Pin 6): Forced Continuous Input. Tie this pin to
ground to force continuous synchronous operation at low
load, to INTV_CC to enable discontinuous mode operation
at low load or to a resistive divider from a secondary output
when using a secondary winding.
I_TH (Pin 7): Current Control Threshold and Error Amplifier
Compensation Point. The current comparator threshold
increases with this control voltage. The voltage ranges
from 0V to 2.4V with 0.8V corresponding to zero sense
voltage (zero current).
SGND (Pin 8): Signal Ground. All small-signal compo-
nents and compensation components should connect to
this ground, which in turn connects to PGND at one point.
I_ON (Pin 9): 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_FB (Pin 10): Error Amplifier Feedback Input. This pin
connects to both the error amplifier input and to the output
of the internal resistive divider. It can be used to attach
additional compensation components if desired.
V_OSENSE (Pin 11): Output Voltage Sense. The output
voltage connects here to the input of the internal resistive
feedback divider.
EXTV_CC (Pin 14): External V_CC Input. When EXTV_CC ex-
ceeds 4.7V, an internal switch connects this pin to INTV_CC
and shuts down the internal regulator so that controller
and gate drive power is drawn from EXTV_CC. Do not exceed
7V at this pin and ensure that EXTV_CC < V_IN.
V_IN (Pin 15): Main Input Supply. Decouple this pin to
PGND with an RC filter (1Ω, 0.1µF).
INTV_CC (Pin 16): Internal 5V Regulator Output. The driver
and control circuits are powered from this voltage. De-
couple this pin to power ground with a minimum of 4.7µF
low ESR tantalum capacitor.
BG (Pin 17): Bottom Gate Drive. Drives the gate of the
bottom N-channel MOSFET between ground and INTV_CC.
PGND (Pin 18): Power Ground. Connect this pin closely to
the source of the bottom N-channel MOSFET, the (–)
terminal of C_VCC and the (–) terminal of C_IN.
SENSE ⁺ (Pin 19): Current Sense Comparator Input. The
(+) input to the current comparator is normally connected
to the SW node unless using a sense resistor (see Appli-
cations Information).
SW (Pin 20): Switch Node. The (–) terminal of the boot-
strap capacitor C_B connects here. This pin swings from a
diode voltage drop below ground up to V_IN.
TG (Pin 21): Top Gate Drive. Drives the top N-channel
MOSFET with a voltage swing equal to INTV_CC superim-
posed on the switch node voltage SW.
BOOST (Pin 22): Boosted Floating Driver Supply. The (+)
terminal of the bootstrap capacitor C_B connects here. This
pin swings from a diode voltage drop below INTV_CC up to
V_IN + INTV_CC.
3711f
7