SI3402-A-GM Silicon Laboratories Inc, SI3402-A-GM Datasheet - Page 11

• 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

3. Functional Description
The Si3402 consists of two major functions: a hotswap
controller/interface
modulated switching regulator (controller and power
FET).
3.1. Overview
The hotswap interface of the Si3402 provides the
complete front end of an 802.3-compliant PD. The
Si3402 also includes two full diode bridges, a transient
voltage
classification current source, and dual-level hotswap
current limiting switch. This high level of integration
enables direct connection to the RJ-45 connector,
simplifies system design, and provides significant
advantages for reliability and protection. The Si3402
requires only four standard external components
(detection resistor, optional classification resistor, load
capacitor, and input capacitor) to create a fully 802.3-
compliant interface. For more information about
supporting higher-power applications, see “AN313:
Using the Si3401/2 in High Power Applications” and
“AN314: Power Combining Circuit for PoE for up to
18.5 W Output”.
The
modulated switching regulator
controller and power FET. The switching regulator
utilizes a constant frequency pulse-width modulated
controller optimized for all possible load conditions in
PoE applications. The regulator integrates a low on-
resistance (Ron) switching power MOSFET that
minimizes power dissipation, increases overall regulator
efficiency, and simplifies system design. An integrated
error amplifier, precision reference, and programmable
soft-start current source provide the flexibility of using a
non-isolated buck regulator topology or an isolated
flyback regulator topology.
CT2/SP2
CT1/SP1
Si3402
surge
integrates
VNEG
POWER LOSS
AND PROTECTION
DIODE BRIDGES
DETECTOR
suppressor,
and
PLOSS
a
a
complete
complete
VPOSF
that includes
detection
Figure 3. Hotswap Block Diagram
VPOSS
12 V
22 V
0 V
12 V
pulse-width-
pulse-width
OFF
ON
CLASSIFICATION
OFF
ON
DETECTION
CONTROL
CONTROL
circuit,
the
Rev. 1.1
RDET
RCL
The Si3402 is designed to operate with both 802.3-
compliant Power Sourcing Equipment (PSE) and pre-
standard (legacy) PSEs that do not adhere to the 802.3
specified inrush current limits. The Si3402 is compatible
with compliant and legacy PSEs because it uses two
levels for the hotswap current limits. By setting the initial
inrush current limit to a low level, a PD based on the
Si3402 minimizes the current drawn from either a
compliant or legacy PSE during startup. After powering
up, the Si3402 automatically switches to a higher-level
current limit, thereby allowing the PD to consume up to
12.95 W (the max power allowed by the 802.3
specification).
The inrush current limit specified by the 802.3 standard
can generate high transient power dissipation in the PD.
By properly sizing the devices and implementing on-
chip thermal protection, the Si3402 can go through
multiple turn-on sequences without overheating the
package or damaging the device. The switching
regulator power MOSFET has been conservatively
designed and sized to withstand the high peak currents
created when converting a high-voltage, low-current
supply
Excessive power cycling or short circuit faults will
engage the thermal overload protection to prevent the
onboard power MOSFETs from exceeding their safe
and reliable operating ranges.
3.2. PD Hotswap Controller
The Si3402 hotswap controller changes its mode of
operation based on the input voltage applied to the CT1
and CT2 pins or the SP1 and SP2 pins, the 802.3-
defined modes of operation, and internal controller
requirements. Table 10 defines the modes of operation
for the hotswap interface.
CURRENT
LIMIT
CENTRAL BIAS
HI/LO
BANDGAP REF
into
HOTSWAP
CONTROL
a
low-voltage,
OFF
ON
10 V
1.23 V
5 V
32 V
39 V
ISOSSFT
STARTUP & BIAS
SWITCHER
high-current
SSFT
Si3402
VREF
IABS
ITC
HSO
supply.
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