ltc3711 Linear Technology Corporation, ltc3711 Datasheet - Page 7

• Manufacturer Part Number: ltc3711
• Description: 5-bit Adjustable, Wide Operating Range, No Rsense? Step-down Controller
• Manufacturer: Linear Technology Corporation

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 2.5 A 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/ F) and the time delay
for overcurrent latchoff (see Applications Information).
Forcing this pin below 0.8V shuts down the device.
V
the on-time comparator. Tying this pin to the output
voltage makes the on-time proportional to V
comparator input defaults to 0.7V when the pin is grounded,
2.4V when the pin is tied to INTV
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
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
defaults to 70mV when this pin is tied to ground, 140mV
when tied to INTV
FCB (Pin 6): Forced Continuous Input. Tie this pin to
ground to force continuous synchronous operation at low
load, to INTV
at low load or to a resistive divider from a secondary output
when using a secondary winding.
I
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
to this pin to set the one-shot timer current and thereby set
the switching frequency.
TH
ON
ON
RNG
U
(Pin 7): Current Control Threshold and Error Amplifier
(Pin 9): On-Time Current Input. Tie a resistor from V
(Pin 3): On-Time Voltage Input. Voltage trip point for
(Pin 5): Sense Voltage Range Input. The voltage at
U
CC
to enable discontinuous mode operation
CC
U
.
CC
. The nominal sense voltage
CC
.
OUT
. The
IN
V
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
voltage connects here to the input of the internal resistive
feedback divider.
EXTV
ceeds 4.7V, an internal switch connects this pin to INTV
and shuts down the internal regulator so that controller
and gate drive power is drawn from EXTV
7V at this pin and ensure that EXTV
V
PGND with an RC filter (1 , 0.1 F).
INTV
and control circuits are powered from this voltage. De-
couple this pin to power ground with a minimum of 4.7 F
low ESR tantalum capacitor.
BG (Pin 17): Bottom Gate Drive. Drives the gate of the
bottom N-channel MOSFET between ground and INTV
PGND (Pin 18): Power Ground. Connect this pin closely to
the source of the bottom N-channel MOSFET, the (–)
terminal of C
SENSE
(+) 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
diode voltage drop below ground up to V
TG (Pin 21): Top Gate Drive. Drives the top N-channel
MOSFET with a voltage swing equal to INTV
posed on the switch node voltage SW.
BOOST (Pin 22): Boosted Floating Driver Supply. The (+)
terminal of the bootstrap capacitor C
pin swings from a diode voltage drop below INTV
V
FB
OSENSE
IN
IN
+ INTV
(Pin 15): Main Input Supply. Decouple this pin to
(Pin 10): Error Amplifier Feedback Input. This pin
CC
CC
+
(Pin 16): Internal 5V Regulator Output. The driver
(Pin 14): External V
(Pin 19): Current Sense Comparator Input. The
(Pin 11): Output Voltage Sense. The output
CC
VCC
.
and the (–) terminal of C
B
connects here. This pin swings from a
CC
Input. When EXTV
CC
B
connects here. This
< V
CC
LTC3711
IN
IN
IN
. Do not exceed
.
.
.
CC
superim-
CC
CC
up to
7
3711f
ex-
CC
CC
.