LTC4259CGW Linear Technology, LTC4259CGW Datasheet - Page 13

• Manufacturer Part Number: LTC4259CGW
• Manufacturer: Linear Technology

Specifications of LTC4259CGW

• Linear Misc Type: Negative Voltage
• Operating Supply Voltage (typ): -48V
• Operating Supply Voltage (max): -57V
• Operating Temperature (min): 0C
• Operating Temperature (max): 70C
• Operating Temperature Classification: Commercial
• Mounting: Surface Mount
• Pin Count: 36
• Lead Free Status / Rohs Status: Not Compliant

APPLICATIO S I FOR ATIO
OVERVIEW
Over the years, twisted-pair Ethernet has become the most
commonly used method for local area networking. The
IEEE 802.3 group, the originator of the Ethernet standard,
has defined an extension to the standard, known as
802.3af, which allows DC power to be delivered simulta-
neously over the same cable used for data communica-
tion. This promises a whole new class of Ethernet devices,
including IP telephones, wireless access points, and PDA
charging stations, which do not require additional AC
wiring or external power transformers, a.k.a. “wall warts.”
With about 13W of power available, small data devices can
be powered by their Ethernet connection, free from AC wall
outlets. Sophisticated detection and power monitoring
techniques prevent damage to legacy data-only devices,
while still supplying power to newer, Ethernet-powered
devices over the twisted-pair cable.
A device that supplies power is called Power Sourcing
Equipment (PSE); a device that draws power from the
wire is called a Powered Device (PD). A PSE is typically
an Ethernet switch, router, hub, or other network switch-
ing equipment that is commonly found in the wiring
closets where cables converge. PDs can take many forms:
digital IP telephones, wireless network access points,
PDA or notebook computer docking stations, cell phone
chargers, and HVAC thermostats are examples of devices
that can draw power from the network.
INTERRUPT
I
2
C
–48V
GND
3.3V
V
INT
SCL
SDAIN
SDAOUT
V
DD
EE
DGND
0.5
SENSE GATE OUT
LTC4259
1/4
IRFM120A
AGND
DETECT
U
10k
S1B
BAV19WS
PSE
U
1k
0.1 F
4
0.22 F
100V
4
W
SMAJ58A
58V
(NETWORK
PHYSICAL
LAYER
CHIP)
PHY
U
Figure 11. System Diagram
RJ45
ROUNDTRIP
SIGNAL PAIR
SIGNAL PAIR
0.05 F MAX
20 MAX
SPARE PAIR
SPARE PAIR
CAT 5
A PSE is required to provide a nominal 48V DC between
either the signal pairs or the spare pairs (but not both) as
shown in Figure 11. The power is applied as a voltage
between two of the pairs, typically by powering the center-
taps of the isolation transformers used to couple the
differential data signals to the wire. Since Ethernet data is
transformer coupled at both ends and is sent differentially,
a voltage difference between the transmit pairs and the
receive pairs does not affect the data. A 10/100base-T
Ethernet connection only uses 2 of the 4 pairs in the cable.
The unused or spare pairs can be powered directly, as
shown in Figure 11, without affecting the data. However,
1000base-T uses all 4 pairs and power must be connected
to the transformer center taps if compatibility with
1000base-T is required.
The LTC4259 provides a complete solution for detection
and powering of PD devices in an IEEE 802.3af compliant
system. The LTC4259 consists of four independent ports,
each with the ability to detect, classify, and provide iso-
lated –48V power to a PD device connected to it. The
LTC4259 senses removal of a PD with IEEE 802.3af
compliant AC or DC methods and turns off –48V power
when the PD is removed. A global control circuit takes care
of system configuration and timing, and uses an I
interface to communicate with the host system.
RJ45
(NETWORK
PHYSICAL
LAYER
CHIP)
PHY
0.1 F
1N4002
SMAJ58A
58V
R
–48V
CLASS
PD
IN
LTC4257
GND
–48V
PWRGD
5 F C
300 F
OUT
LTC4259
IN
CONVERTER
DC/DC
13
4259i
V
4259 F11
2
OUT
+
–
C