SI3400 Datasheet, PDF (15/20 Pages) Silicon Laboratories – FULLY-INTEGRATED 802.3-COMPLIANT PD INTERFACE AND SWITCHING REGULATOR

4. Pin Descriptions
Si3400/Si3401
20 19 18 17 16 15
EROUT 1
SSFT 2
VDD ³
ISOSSFT 4
VNEG
(PAD)
14 CT1
13 CT2
12 VPOSF
11 SP1
5 6 7 8 9 10
Pin#
1
2
3
4
5
6
7
8
9, Pad
10
11
12
13
14
15
16
17
18
19
20
Name
EROUT
SSFT
VDD
ISOSSFT
PLOSS
RDET
HSO
RCL
VNEG
SP2
SP1
VPOSF
CT2
CT1
VSSA
VPOSS
VSS1
SWO
VSS2
FB
Table 11. Si3400 and Si3401 Pin Descriptions (Top View)
Description
Error-amplifier output and PWM input; directly connected to opto-coupler in isolated application.
Soft-start output pin ramps voltage across external soft-start capacitor to allow switcher to ramp
output slowly.
5 V supply rail for switcher; provides drive for opto-coupler.
Isolated mode soft start enable input. Tie to VDD for non-isolated applications. Connect a
0.1 µF capacitor between this pin and VSSA for isolated applications.
Early power loss indicator; open drain output is pulled to VPOS when VPORT is applied.
Input pin for external precision detection resistor; also used for establishing absolute current ref-
erence.
Hotswap switch output; connects to VNEG through hotswap switch.
Input pin for external precision classification resistor; float if optional RCLASS is unused.
Rectified high-voltage supply, negative rail. Must be connected to thermal PAD node (VNEG)
on package bottom. This thermal pad must be connected to VNEG (pin #9) as well as a 2 in²
heat spreader plane using a minimum of nine thermal vias.
High-voltage supply input from spare pair; polarity-insensitive.
High-voltage supply input from spare pair; polarity-insensitive.
Rectified high-voltage supply, positive rail (force node)
High-voltage supply input from center tap of Ethernet transformer; polarity-insensitive.
High-voltage supply input from center tap of Ethernet transformer; polarity-insensitive.
Analog ground.
Rectified high-voltage supply, positive rail sense node.
Negative supply rail for switcher; externally tied to HSO.
Switching transistor output; drain of switching N-FET.
Negative supply rail for switcher; externally tied to HSO.
Regulated feedback input in non-isolated application.
Rev. 0.9
15