6
LTC3717-1
sn37171 37171fs
UU
U
PI FU CTIO S
V
ON
(Pin 1): 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 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)/Exposed Pad (Pin 33): Signal Ground. All
small-signal components and compensation components
should connect to this ground, which in turn connects to
PGND at one point. Pin 5 is electrically connected to the
exposed pad. Exposed pad must be soldered to PCB.
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
.
NC (Pins 8, 9, 11, 12, 13, 14, 22, 25, 26, 29, 30, 32): Do
Not Connect.
V
REF
(Pin 10): 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 15): External V
CC
Input. When EXTV
CC
exceeds 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 16): Main Input Supply. Decouple this pin to
PGND with an RC filter (1Ω, 0.1µF).
INTV
CC
(Pin 17): Internal Regulator Output. The control
circuits are powered from this voltage when V
IN
is greater
than 5V. Decouple this pin to power ground with a mini-
mum of 4.7µF low ESR tantalum or ceramic capacitor.
DRV
CC
(Pin 18): Voltage Supply to Bottom Gate Driver.
Normally connected to the INTV
CC
pin through a decoup-
ling RC filter (1Ω/0.1µF). Decouple this pin to power ground
with a minimum of 4.7µF low ESR tantalum or ceramic
capacitor. Do not exceed 7V at this pin.
BG (Pin 19): Bottom Gate Drive. Drives the gate of the
bottom N-channel MOSFET between ground and DRV
CC
.
PGND (Pin 20): Power Ground. Connect these pins closely
to the source of the bottom N-channel MOSFET, the (–)
terminal of C
VCC
and the (–) terminal of C
IN
.
SENSE
–
(Pin 21): Negative Current Sense Comparator
Input. The (–) input to the current comparator is normally
connected to power ground unless using a resistive di-
vider from INTV
CC
(see Applications Information).
SENSE
+
(Pin 23): Positive Current Sense Comparator
Input. The (+) input to the current comparator is normally
connected to the SW node unless using a sense resistor
(see Applications Information).
SW (Pin 24): 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 27): 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.
