LT4276
6
4276fa
For more information www.linear.com/LT4276
pin FuncTions
GND(Pins 1, 19, Exposed Pad Pin 29): Device Ground.
Exposed Pad must be electrically and thermally connected
to PCB GND and Pin 19.
RCLASS
++
(Pin 3, LT4276A Only): LTPoE
++
Class Select
Input. Connect a resistor between RCLASS
++
to GND per
Table 1.
AUX (Pin 2): Auxiliary Sense. Assert AUX via a resistive
divider from the auxiliary power input to set the voltage
at which the auxiliary supply takes over. Asserting AUX
pulls down HSGATE, disconnects the signature resistor
and disables classification. The AUX pin sinks I
AUXH
when
below its threshold voltage of V
AUXT
to provide hysteresis.
Connect to GND if not used.
RCLASS (Pin 4): Class Select Input. Connect a resistor
between RCLASS to GND per Table 1.
T2P (Pin 5, LT4276A and LT4276B only): PSE Type Indica
-
tor. Low impedance to V
CC
indicates 2-event classification.
Alternating low/high impedance indicates LTPoE
++
clas-
sification (LT4276A only, see Applications Information).
High impedance indicates
1-
event classification. This pin
is not connected on the LT4276C. See the Applications
Information Section for pin behavior when using the AUX
pin.
DNC (Pin 22): Do Not Connect. Leave pin open.
ROSC (Pin 10): Programmable Frequency Adjustment.
Resistor to GND programs operating frequency. Leave
open for default frequency of 214kHz.
SFST (Pin 11): Soft-Start. Capacitor to GND sets soft-
start timing.
FFSDLY (Pin 12): Forward/Flyback Select and Primary
Gate Delay Adjustment. Resistor to GND adjusts gate drive
delay for a flyback topology. Resistor to V
CC
adjusts gate
drive delay for a forward topology.
ITHB (Pin 13): Current Threshold Control. The voltage on
this pin corresponds to the peak current of the external
FET. Note that the voltage gain from ITHB to the input of
the current sense comparator (V
SENSE
) is negative.
FB31 (Pin 14): Feedback Input. In flyback mode, connect
external resistive divider from the third winding feedback.
Reference voltage is 3.17V. Connect to GND in forward
mode.
RLDCMP (Pin 15): Load Compensation Adjustment. Op
-
tional resistor to GND controls output voltage set point
as a function of peak switching current. Leave RLDCMP
open if load compensation is not needed.
ISEN
–
(Pin 16): Current Sense, Negative Input. Route as
a dedicated trace to the current sense resistor.
ISEN
+
(Pin 17): Current Sense, Positive Input. Route as
a dedicated trace to the current sense resistor.
SG (Pin 18): Secondary (Synchronous) Gate Drive, Output.
PG (Pin 20): Primary Gate Drive, Output.
V
CC
(Pins 6, 7, 8, 9, 21): Switching Regulator Controller
Supply Voltage. Connect a local 1µF ceramic capacitor
from V
CC
pin 21 to GND pin 19 as close as possible to
LT4276 as shown in Table 2.
SWVCC(Pin 23): Switch Driver for V
CC
’s Buck Regulator.
This pin drives the base of a PNP in a buck regulator to
generate V
CC
.
V
IN
(Pin 24): Buck Regulator Supply Voltage. Usually
separated from HSSRC by a pi filter.
HSSRC (Pin 25): External Hot Swap MOSFET Source.
Connect to source of the external MOSFET.
HSGATE (Pin 26): External Hot Swap MOSFET Gate Con
-
trol, Output. Capacitance to GND determines inrush time.
NC (Pin 27)
:
No Connection. Not internally connected.
VPORT (Pin 28): PD Interface Supply Voltage and External
Hot Swap MOSFET Drain Connection.
