LTC4267-1
4
42671fa
For more information www.linear.com/4267-1
elecTrical characTerisTics
The l denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. (Note 3)
SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS
I
LIM_HI
Input Current Limit, High Level V
PORTN
= –48V, P
OUT
= –43V (Note 13, 14)
l
350 450 mA
I
LIM_LO
Input Current Limit, Low Level V
PORTN
= –48V, P
OUT
= –43V (Note 13, 14)
l
90 205 mA
f
OSC
Oscillator Frequency V
ITH
/RUN – PGND = 1.3V, P
VCC
– PGND = 8V 180 200 240 kHz
DC
ON(MIN
) Minimum Switch On Duty Cycle V
ITH
/RUN – PGND = 1.3V, V
FB
– PGND = 0.8V,
P
VCC
– PGND = 8V
6 8 %
DC
ON(MAX)
Maximum Switch On Duty Cycle V
ITH
/RUN – PGND = 1.3V, V
FB
– PGND = 0.8V,
P
VCC
– PGND = 8V
70 80 90 %
t
RISE
NGATE Drive Rise Time C
LOAD
= 3000pF, P
VCC
– PGND = 8V 40 ns
t
FALL
NGATE Drive Fall Time C
LOAD
= 3000pF, P
VCC
– PGND = 8V 40 ns
V
IMAX
Peak Current Sense Voltage R
SL
= 0, P
VCC
– PGND = 8V (Note 15)
l
90 100 115 mV
I
SLMAX
Peak Slope Compensation Output Current P
VCC
– PGND = 8V (Note 16) 5 µA
t
SFST
Soft-Start Time P
VCC
– PGND = 8V 1.4 ms
T
SHUTDOWN
Thermal Shutdown Trip Temperature (Notes 13, 17) 140 °C
Note 1: Stresses beyond those listed under Absolute Maximum Ratings
may cause permanent damage to the device. Exposure to any Absolute
Maximum Rating condition for extended periods may affect device
reliability and lifetime.
Note 2: P
VCC
internal clamp circuit self regulates to 9.4V with respect to
PGND.
Note 3: The LTC4267-1 operates with a
negative supply voltage in the
range of –
1.5V to – 57V. To avoid confusion, voltages for the PD interface
are always referred to in terms of absolute magnitude. Terms such as
“maximum negative voltage” refer to the largest negative voltage and
a “rising negative voltage” refers to a voltage that is becoming more
negative.
Note 4: The LTC4267-1 is designed to work with two polarity protection
diode drops between the PSE and PD. Parameter ranges specified in the
Electrical Characteristics section are with respect to this product pins and
are designed to meet IEEE 802.3af specifications when these diode drops
are included. See the Application Information section.
Note 5: Signature resistance is measured via the two-point ∆V/∆I method
as defined by IEEE 802.3af. The PD signature resistance is offset from
the 25k to account for diode resistance. With two series diodes, the total
PD resistance will be between 23.75k and 26.25k and meet IEEE 802.3af
specifications. The minimum probe voltages measured at the LTC4267-1
pins are –1.5V and –2.5V. The maximum probe voltages are –8.5V and
–9.5V.
Note 6: The PD interface includes hysteresis in the UVLO voltages to
preclude any start
-up oscillation. Per IEEE 802.3af requirements, the PD
will power up from a voltage sour
ce with 20Ω series resistance on the first
trial.
Note 7: Dynamic Supply current is higher due to the gate charge being
delivered at the switching frequency.
Note 8: I
VPORTN_CLASS
does not include classification current
programmed at the R
CLASS
pin. Total current in classification mode will be
I
VPORTN_CLASS
+ I
CLASS
(See Note 9).
Note 9: I
CLASS
is the measured current flowing through R
CLASS
. ∆I
CLASS
accuracy is with respect to the ideal current defined as I
CLASS
= 1.237/
R
CLASS
. The current accuracy does not include variations in R
CLASS
resistance. The total classification current for a PD also includes the IC
quiescent current (I
VPORTN_CLASS
). See Applications Information.
Note 10: To disable the 25k signature, tie SIGDISA to V
PORTP
or hold
SIGDISA high with respect to V
PORTN
. See Applications Information.
Note 11: The switching regulator is tested in a feedback loop that servos
V
FB
to the output of the error amplifier while maintaining I
TH
/RUN at the
midpoint of the current limit range.
Note 12: I
POUT_LEAK
includes current drawn through P
OUT
by the power
good status circuit. This current is compensated for in the 25k signature
resistance and does not affect PD operation.
Note 13:
The LTC4267-1 PD Interface includes thermal protection. In
the event of an overtemperature condition, the PD interface will turn off
the switching regulator until the part cools below the overtemperature
limit. The LTC4267-1 is also protected against thermal damage from
incorrect classification probing by the PSE. If the LTC4267-1 exceeds the
overtemperature threshold, the classification load current is disabled.
Note 14: The PD interface includes dual level input current limit. At turn-
on, before the P
OUT
load capacitor is charged, the PD current level is set
to a low level. After the load capacitor is charged and the P
OUT
– V
PORTN
voltage difference is below the power good threshold, the PD switches to
high level current limit. The PD stays in high level current limit until the
input voltage drops below the UVLO turn-off threshold.
Note 15: Peak current sense voltage is reduced dependent on duty cycle
and an optional external resistor in series with the SENSE pin (R
SL
). For
details, refer to the programmable slope compensation feature in the
Applications Information section.
Note 16: Guaranteed by design.
Note 17: The PD interface includes overtemperature protection that
is
intended to protect the device from momentar
y overload conditions.
Junction temperature will exceed 125°C when overtemperature protection
is active. Continuous operation above the specified maximum operating
junction temperature may impair device reliability.
