LTC4269-1
9
42691fc
TEMPERATURE (°C)
–50
t
ON(MIN)
(ns)
330
25
42691 G28
300
280
–25 0 50
270
260
340
320
310
290
75 100 125
R
tON(MIN)
= 158k
TEMPERATURE (°C)
–50
0
t
PGDLY
(ns)
50
150
200
250
0
50
75
42691 G29
100
–25 25
100 125
300
R
PGDLY
= 16.9k
R
PGDLY
= 27.4k
TEMPERATURE (°C)
–50
t
ENDLY
(ns)
285
305
325
25 75
42691 G30
265
245
–25 0
50 100 125
225
205
R
ENDLY
= 90k
TYPICAL PERFORMANCE CHARACTERISTICS
Minimum PG On-Time
vs Temperature
PG Delay Time vs Temperature
Enable Delay Time
vs Temperature
PIN FUNCTIONS
SHDN (Pin 1): Shutdown Input. Use this pin for auxiliary
power application. Drive SHDN high to disable the PD
interface operation and corrupt the signature resistance.
If unused, tie SHDN to V
PORTN
.
T2P (Pin 2): Type 2 PSE Indicator, Open-Drain. Low imped-
ance indicates the presence of a Type 2 PSE.
R
CLASS
(Pin 3): Class Select Input. Connect a resistor
between R
CLASS
and V
PORTN
to set the classifi cation load
current (see Table 2).
NC (Pins 4, 7, 8, 25, 28, 31): No Connect.
V
PORTN
(Pins 5, 6): Input Voltage, Negative Rail. Pin 5 and
Pin 6 must be electrically tied together at the package.
SG (Pin 9): Synchronous Gate Drive Output. This pin
provides an output signal for a secondary-side synchro-
nous rectifi er. Large dynamic currents may fl ow during
voltage transitions. See the Applications Information
section for details.
V
CC
(Pin 10): Supply Voltage Pin. Bypass this pin to
GND with a 4.7µF, or more, capacitor. This pin has a 19.5V
clamp to ground. V
CC
has an undervoltage lockout func-
tion that turns the part on when V
CC
is approximately
15.3V and off at 9.7V. In a conventional trickle-charge
bootstrapped confi guration, the V
CC
supply current
increases signifi cantly during turn-on causing a benign
relaxation oscillation action on the V
CC
pin if the part does
not start normally.
t
ON
(Pin 11): Pin for external programming resistor to
set the minimum time that the primary switch is on for
each cycle. Minimum turn-on facilitates the isolated feed-
back method. See the Applications Information section
for details.
ENDLY (Pin 12): Pin for external programming resistor to
set enable delay time. The enable delay time disables the
feedback amplifi er for a fi xed time after the turn-off of the
primary-side MOSFET. This allows the leakage inductance
voltage spike to be ignored for fl yback voltage sensing.
See the Applications Information section for details.
SYNC (Pin 13): External Sync Input. This pin is used to
synchronize the internal oscillator with an external clock.
The positive edge of the clock causes the oscillator to
discharge causing PG to go low (off) and SG high (on). The
sync threshold is typically 1.5V. Tie to ground if unused.
See the Applications Information section for details.
SFST (Pin 14): Soft-Start. This pin, in conjunction with a
capacitor (C
SFST
) to GND, controls the ramp-up of peak
primary current through the sense resistor. It is also used
to control converter inrush at start-up. The SFST clamps
