SI3461-E01-GM Silicon Laboratories Inc, SI3461-E01-GM Datasheet - Page 14

• Manufacturer Part Number: SI3461-E01-GM
• Description: IC POWER MANAGEMENT CTLR 11VQFN
• Manufacturer: Silicon Laboratories Inc

Specifications of SI3461-E01-GM

• Applications: Power Sourcing Equipment (PSE)
• Current - Supply: 500mA
• Voltage - Supply: 2.7 V ~ 3.6 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 11-VQFN
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

Si3461
5.4. Overload Protection
The Si3461 implements a two-level overload protection scheme. The output current is limited to ILIM, and the
output is shut down if the current exceeds ICUT for more than 60 ms. If current limitation persists for more than
15 ms in case of PoE+ Class 4 loads, the output is shut down to protect the pass FET. Current limit values are
dynamically set according to the power level granted during the classification process and the effective output
voltage (refer to Table 4 on page 7 for current limit values).
A special 425 mA current limit applies until the FET is fully turned on. If the FET does not fully turn on in the first
75 ms due to an overload condition, an error is declared. The maximum time that the 425 mA inrush current is
supplied is about 70 ms due to a 5 ms period to initially ramp the FET gate voltage.
The overload protection is implemented using a timer with a timeout set to 60 ms. If the output current exceeds the
I
threshold, the timer counts up; otherwise, if the output current drops below ICUT, the timer counts down
CUT
towards zero at 1/16th the rate. If the timer reaches the set timeout, an overcurrent fault is declared; the channel is
shut down (by turning off the external pass FET), and the status LED flashes rapidly at a rate of 10 Hz.
If the Si3461 was configured in the “automatic restart” mode during start-up, it will automatically resume the
detection process after 2.2 seconds. In the “restart after disconnect” mode of operation, the status LED will flash
rapidly, and the Si3461 will not resume detection until it senses a resistance higher than 150 k. This condition can
normally be achieved by removing the Ethernet cable from the Si3461-EVB's RJ-45 jack labeled “PoE”. Then, the
detection process begins; the status LED blinks at a rate of 1.5 Hz, and the Si3461 is allowed to go into
classification and power-up mode if a valid PD signature resistance is detected.
5.5. Disconnect
The Si3461 implements a robust disconnect algorithm. If the output current level drops below 7.5 mA typical for
more than 350 ms, the Si3461 declares a PD disconnect event, and the pass FET is turned off. The Si3461
automatically resumes the detection process after 500 ms.
5.6. UVLO and OVLO
The Si3461-EVB reference design is optimized for 50 V nominal input voltages (44 V minimum to 57 V maximum).
If the input voltage drops below 42 V, a UVLO condition is declared, which generates the error condition (LED
flashing rapidly). An undervoltage event is a fault condition reported through the status LED as a rapid blinking of
10 flashes per second. In the same way, if the input voltage exceeds 60 V, an OVLO condition is declared. In both
cases, the output is shut down.
The UVLO and OVLO conditions are continuously monitored in all operating states.
5.7. Status LED Function
During the normal detection sequence, the STATUS LED flashes at approximately 1.5 times per second as the
detection process continues. After successful power up, the LED glows continuously. If there is an error condition
(i.e., class level is beyond programmed value or a fault or over current condition has been detected), the LED
flashes rapidly at 10 times per second. This occurs for two seconds for normal error delay, and the detection
process will automatically start again after 2.2 s unless a “restart after disconnect condition” was set during the
initial configuration. Power will not be provided until an open circuit condition is detected. Once the Si3461-EVB
detects an open circuit condition, the LED blinks at 1.5 times per second.
If the Powered Device (PD) is disconnected so that a disconnect event occurs, the LED will start flashing at 1.5
times per second once the detect process resumes.
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