SI3402-A-GM Silicon Laboratories Inc, SI3402-A-GM Datasheet - Page 14

• Manufacturer Part Number: SI3402-A-GM
• Description: IC POE PD LOW EMI SW REG 20VQFN
• Manufacturer: Silicon Laboratories Inc
• Type: Power over Ethernet Switch (PoE)r

Specifications of SI3402-A-GM

• Package / Case: 20-VQFN
• Applications: IP Phones, Power over LAN, Network Routers and Switches
• Internal Switch(s): Yes
• Current Limit: 470mA
• Voltage - Supply: 2.8 V ~ 57 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Product: PoE / LAN Solutions
• Supply Voltage (max): 57 V
• Supply Voltage (min): 2.8 V
• Power Dissipation: 1.2 W
• Operating Temperature Range: - 40 C to + 85 C
• Mounting Style: SMD/SMT
• Operating Temperature (min): -40C
• Operating Temperature Classification: Industrial
• Operating Temperature (max): 85C
• Rad Hardened: No
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant, Lead free / RoHS Compliant

Si3402
3.2.6. Power Loss Indicator
A situation can occur in which power is lost at the input
of the diode bridge and the hotswap controller does not
detect the fault due to the VPOS to VNEG capacitor
maintaining the voltage. In such a situation, the PD can
remain operational for hundreds of microseconds
despite the PSE having removed the line voltage. If it is
recognized early enough, the time from power loss to
power failure can provide valuable time to gracefully
shut down an application.
Due to integration of the diode bridges, the Si3402 is
able to instantaneously detect the removal of the line
voltage and provide that early warning signal to the PD
application. The PLOSS pin is an open drain output that
pulls up to VPOS when a line voltage greater than 27 V
is applied. When the line voltage falls below 27 V, the
output becomes high-impedance, allowing an external
pull-down resistor to change the logic state of PLOSS.
The benefit of this indicator is that the powered device
may include a microcontroller that can quickly save its
memory or operational state before draining the supply
capacitors and powering itself down. This feature can
help improve overall manageability in applications, such
as wireless access points.
3.3. Switching Regulator
Power over Ethernet (PoE) applications fall into two
broad categories, isolated and non-isolated. Non-
isolated systems can be used when the powered device
is self-contained and does not provide external
conductors to the user or another application. Non-
isolated applications include wireless access points and
14
SSFT
VREF
IABS
FB
ITC
ERROR
AMPLIFIER
OSCILLATOR
STARTUP & BIAS
SWITCHER
HSO
Figure 4. Switcher Block Diagram
EROUT
VDD
MODULATOR
Rev. 1.1
ISOSSFT
VPOSF
PULSE-
WIDTH
security cameras. In these applications, there is no
explicit need for dc isolation between the switching
regulator output and the hotswap interface. An isolated
system must be used when the powered device
interfaces with other self-powered equipment or has
external conductors accessible to the user or other
applications. For proper operation, the regulated output
supply of the switching regulator must not have a dc
electrical path to the hotswap interface or switching
regulator primary side. Isolated applications include
point-of-sale terminals where the user can touch the
grounded metal chassis.
The application determines the converter topology. An
isolated application will require a flyback transformer-
based
application can use an inductor-based buck converter
topology. In the isolated case, dc isolation is achieved
through a transformer in the forward path and a voltage
reference plus opto-isolator in the feedback path. The
application circuit shown in Figure 2 is an example of
such a topology. The non-isolated application in
Figure 1 makes use of a single inductor as the energy
conversion element, and the feedback signal is directly
supplied into the internal error amplifier. As can be seen
from the application circuits, the isolated topology has
an increased number of components, thus increasing
the bill of materials (BOM) and system footprint.
To optimize cost and ease implementation, each
application should be evaluated for its isolated or non-
isolated requirements.
VPOSS
VSSA
switching
SWITCH
DRIVE
topology
VSS1
VSS2
while
SWO
a
non-isolated