ltc3717-1 Linear Technology Corporation, ltc3717-1 Datasheet - Page 6

• Manufacturer Part Number: ltc3717-1
• Description: Wide Operating Range, No Rsense Step-down Controller For Ddr/qdr Memory Termination
• Manufacturer: Linear Technology Corporation

PI FU CTIO S
LTC3717-1
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 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
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
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 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
to this pin to set the one-shot timer current and thereby set
the switching frequency.
V
connects to V
through precision internal resistors before it is applied to
the input of the error amplifier. Do not apply more than
1.5V on V
resistor R2 (1/2 • R1 at V
NC (Pins 8, 9, 11, 12, 13, 14, 22, 25, 26, 29, 30, 32): Do
Not Connect.
V
This pin connects to an external reference and divides its
voltage to 1/3 V
before it is applied to the positive input of the error
amplifier. Reference voltage for output voltage, power
6
TH
ON
ON
RNG
FB
REF
U
(Pin 4): Current Control Threshold and Error Amplifier
(Pin 6): On-Time Current Input. Tie a resistor from V
(Pin 1): On-Time Voltage Input. Voltage trip point for
(Pin 7): Error Amplifier Feedback Input. This pin
(Pin 10): Positive Input of Internal Error Amplifier.
(Pin 3): Sense Voltage Range Input. The voltage at
FB
U
. For higher output voltages, attach an external
OUT
REF
CC
and divides its voltage to 2/3 • V
U
.
through precision internal resisters
REF
CC
) from V
. The nominal sense voltage
CC
.
OUT
to V
FB
.
OUT
. The
FB
IN
good threshold, and short-circuit shutdown threshold. Do
not apply more than 3V on V
used, connect an external resistor (R1
voltage reference to V
EXTV
exceeds 4.7V, an internal switch connects this pin to
INTV
controller and gate drive power is drawn from EXTV
not exceed 7V at this pin and ensure that EXTV
V
PGND with an RC filter (1 , 0.1 F).
INTV
circuits are powered from this voltage when V
than 5V. Decouple this pin to power ground with a mini-
mum of 4.7 F low ESR tantalum or ceramic capacitor.
DRV
Normally connected to the INTV
ling RC filter (1 /0.1 F). Decouple this pin to power ground
with a minimum of 4.7 F 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
PGND (Pin 20): Power Ground. Connect these pins closely
to the source of the bottom N-channel MOSFET, the (–)
terminal of C
SENSE
Input. The (–) input to the current comparator is normally
connected to power ground unless using a resistive di-
vider from INTV
SENSE
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
diode voltage drop below ground up to V
TG (Pin 27): Top Gate Drive. Drives the top N-channel
MOSFET with a voltage swing equal to INTV
posed on the switch node voltage SW.
IN
(Pin 16): Main Input Supply. Decouple this pin to
CC
CC
CC
CC
–
+
(Pin 18): Voltage Supply to Bottom Gate Driver.
(Pin 17): Internal Regulator Output. The control
and shuts down the internal regulator so that
(Pin 15): External V
(Pin 21): Negative Current Sense Comparator
(Pin 23): Positive Current Sense Comparator
VCC
CC
and the (–) terminal of C
B
connects here. This pin swings from a
(see Applications Information).
REF
.
REF
CC
CC
. If higher voltages are
Input. When EXTV
pin through a decoup-
IN
IN
.
.
CC
160k) from
IN
sn37171 37171fs
CC
is greater
superim-
< V
CC
. Do
IN
CC
CC
.
.