SI3461-KIT Silicon Laboratories Inc, SI3461-KIT Datasheet - Page 8

• Manufacturer Part Number: SI3461-KIT
• Description: BOARD EVAL FOR SI3461
• Manufacturer: Silicon Laboratories Inc
• Type: Controllers & Processorsr

Specifications of SI3461-KIT

• Main Purpose: Special Purpose DC/DC, Power Over Ethernet
• Board Type: Fully Populated
• Utilized Ic / Part: Si3461
• Ethernet Connection Type: 10/100 Base-T, IEEE 802.3
• Interface Type: Ethernet
• Operating Voltage: 12 V to 15 V
• Operating Current: 10 mA
• Product: Modules
• For Use With/related Products: Si3460
• Lead Free Status / RoHS Status: Lead free / RoHS non-compliant
• Current - Output: -
• Voltage - Output: -
• Voltage - Input: -
• Power - Output: -
• Frequency - Switching: -
• Outputs And Type: -
• Regulator Topology: -
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant
• Other names: 336-1843

Si3461-EVB
After power-up, the STATUS pin of the Si3461 is in a high-impedance state and is used for measuring the voltage
set by the DIP switch and the associated resistor network. Then, during normal operation, this pin drives the status
LED via transistor Q3.
The mode setting voltage steps are provided by a simple 4-bit DAC. Each mode setting resistor should be
connected either to GND or +3.3 V for proper operation. Take care not to short the +3.3 V supply to GND, and
remember to activate the reset button for the new configuration to take effect.
The voltage thresholds found in Table 2 take into account the slight loading effect of Q3's base current; therefore, it
is recommended to use the same source resistance (around 2.0 k) as that of the Si3461-EVB network when
providing the status pin voltage from a different voltage source, such as a simple voltage divider or a DAC. Different
resistor values may be used in the mode setting network, but the trade-off between voltage step accuracy and the
additional worst-case supply current should be considered. For high value resistors, the base current will alter the
voltage steps, while low value resistors may place higher loads on the STATUS pin when driving the LED.
6.2. Detection
The detection process consists of sensing a nominal 25 k signature resistance in parallel with up to 0.15 µF of
capacitance. The signature resistance measurement has to be carried out in the 2.8 to 10 V output voltage range
with a 5 mA current limit.
To eliminate the possibility of false detection events, the Si3461-EVB reference design performs a robust 3-point
detection sequence by varying the voltage across the load and sensing the load current changes. This minimizes
effects, such as those caused by the diode bridges present in powered devices (PDs).
At the beginning of the detection sequence, V
20+20+50 ms at each respective level. If the PD's signature resistance is in the RGOOD range of 17 to 29 k, the
Si3461 proceeds to classification and powerup. If the PD resistance is not in this range, the detection sequence
repeats continuously.
Detection is sequenced approximately every 360 ms until RGOOD is sensed, indicating a valid PD has been
detected. The STATUS LED (D2) is flashed at an approximate rate of 1.5 Hz to indicate that the PSE is searching
for a valid PD.
6.3. Classification
During classification, the PSE interrogates the PD to determine its power requirement. This procedure has to be
carried out in the 15.5 to 20.5 V output voltage range with a 75 mA current limit. The current measured during the
classification process determines the class level of the PD.
The Si3461 implements both the one-event and two-event physical layer classification methods. For one-event
classification, the pass FET Q4 is turned on and programmed for an output voltage of 18 V with a current limit of
75 mA for 30 ms. For the two-event classification, the 18 V pulse is output twice with an 8.5 V amplitude mark
pulse for 10 ms between the two classification pulses.
If the available power set by the initial voltage on the Si3461's STATUS pin during startup is 30 W, the Si3461-EVB
first attempts to classify a Type 2 PD using the two-event method. If, at the end of the first event, something other
than a Class 4 PD was detected, the second event is not generated, and the device is classified based on the
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DIP Switch
Configuration
2.618 to 2.838
2.838 to 3.044
Voltage (V)
Status Pin
> 3.044
Table 2. Operating Modes (Continued)
PSE Type
1
1
2
OUT
is at zero; then, it is varied from 4 to 8 V and back to 4 V for
Rev. 0.5
Midspan/
Endpoint
Endpoint
Endpoint
Endpoint
Operating Mode
Restart Action on Fault or
Overload Event Condition
Auto restart after 2 s
Auto restart after 2 s
Auto restart after 2 s
Power (W)
Available
15.4
30
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