Datasheet

6
LTC3717
sn3717 3717fs
UU
U
PI FU CTIO S
RUN/SS (Pin 1): 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.
PGOOD (Pin 2): Power Good Output. Open drain logic
output that is pulled to ground when the output voltage is
not within ±10% of the regulation point.
V
RNG
(Pin 3): 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
.
I
TH
(Pin 4): 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 5): 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 6): 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 7): Error Amplifier Feedback Input. This pin
connects to V
OUT
and divides its voltage to 2/3 • V
FB
through precision internal resistors before it is applied to
the input of the error amplifier. Do not apply more than
1.5V on V
FB
. For higher output voltages, attach an external
resistor R2 (1/2 • R1 at V
REF
) from V
OUT
to V
FB
.
V
REF
(Pin 8): Positive Input of Internal Error Amplifier.
This pin connects to an external reference and divides its
voltage to 1/3 V
REF
through precision internal resisters
before it is applied to the positive input of the error
amplifier. Reference voltage for output voltage, power
good threshold, and short-circuit shutdown threshold. Do
not apply more than 3V on V
REF
. If higher voltages are
used, connect an external resistor (R1 ≥ 160k) from
voltage reference to V
REF
.
EXTV
CC
(Pin 9): 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
CC
.
V
CC
(Pin 10): Bias Input Supply. 4V to 36V operating
range. Decouple this pin to PGND with an RC filter (1Ω,
0.1µF).
INTV
CC
(Pin 11): 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 or ceramic capacitor.
BG (Pin 12): Bottom Gate Drive. Drives the gate of the
bottom N-channel MOSFET between ground and INTV
CC
.
PGND (Pin 13): 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
.
SW (Pin 14): 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 a diode voltage
drop above V
IN
.
TG (Pin 15): 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 16): 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
.