si3400 Silicon Laboratories, si3400 Datasheet - Page 16

• Manufacturer Part Number: si3400
• Description: Fully-integrated 802.3-compliant Pd Interface And Switching Regulator
• Manufacturer: Silicon Laboratories

Si3400/Si3401
4. Pin Descriptions
16
9, Pad
Pin#
10
12
13
14
15
16
17
18
19
20
11
1
2
3
4
5
6
7
8
ISOSSFT
EROUT
VPOSF
VPOSS
PLOSS
VNEG
Name
RDET
SSFT
VSSA
VSS1
VSS2
SWO
HSO
VDD
RCL
SP2
SP1
CT2
CT1
FB
Table 12. Si3400 and Si3401 Pin Descriptions (Top View)
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.
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 in
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.
Isolated mode soft start enable input. Tie to VDD for non-isolated applications. Connect a
ISOSSFT
EROUT
SSFT
VDD
1
2
3
4
20
5
Preliminary Rev. 0.91
19
6
18
VNEG
(PAD)
7
17
8
16
9
Description
15
10
14
13
12
11
CT2
CT1
VPOSF
SP1
2