+54 V
Unused
7 6 5 4 3 2
1
JP2 AUTO MODE SEL
7 6 5 4 3
2
1
7 6 5 4
3
2 1
JP1
EXT
+5VDC SEL
USB
+5 V
4pp Class 8 90W
4pp Class 7 75W
4pp Class 6 60W
7 6 5
4
3 2 1
7 6
5
4 3 2 1
4pp Class 5 45W
4pp Class 4 30W
B
O
T
T
O
P
VOUT8
VOUT7
VOUT6
VOUT5
VOUT4
VOUT3
VOUT2
VOUT1
VOUT2
VOUT1
VOUT3
VOUT4
VOUT5
VOUT6
VOUT7
VOUT8
Figure 1.5. No I
2
C Host, Four 802.3bt 4-Pair Ports
The following figure shows the use case where the Si3474 is with an I
2
C Host. In this case, all JP2 AUTO MODE SEL jumpers are
removed to indicate a Hosted I
2
C operation mode. The selection jumpers on the POE_BT_CB will need to be set up, depending on the
expected programming of bits 4 and 7 of Register 0x29 on both quads. One power supply is needed for this configuration. The +54 V
provides power to PDs as well as to the Si3474 VPWR. The JP1 jumper is placed so that the +5 V supply is derived from USB. The 5 V
USB rail supplies power to the Si3474 VDD (albeit indirectly through isolation).
USB Type
A
USB Micro
Type B
+54V
JP2 AUTO MODE SEL
JP1
EXT
+5VDC SEL
USB
7 6 5 4 3 2 1
Hosted
B
O
T
T
O
P
VOUT8
VOUT7
VOUT6
VOUT5
VOUT4
VOUT3
VOUT2
VOUT1
VOUT1
VOUT3
VOUT5
VOUT7
VOUT2
VOUT4
VOUT6
VOUT8
I
2
C Addr[0] = 0
Reg 0x29[4] = 0
I
2
C Addr[0] = 0
Reg 0x29[7] = 0
I
2
C Addr[0] = 1
Reg 0x29[4] = 0
I
2
C Addr[0] = 1
Reg 0x29[7] = 0
I
2
C Addr[0] = 0
Reg 0x29[4] = 1
I
2
C Addr[0] = 0
Reg 0x29[7] = 1
I
2
C Addr[0] = 1
Reg 0x29[4] = 1
I
2
C Addr[0] = 1
Reg 0x29[7] = 1
Eight 802.3at
B
O
T
T
O
P
VOUT2
VOUT1
VOUT3
VOUT4
VOUT5
VOUT6
VOUT7
VOUT8
Four 802.3bt
I
2
C Addr[0] = 0
Reg 0x29[4] = 1
I
2
C Addr[0] = 0
Reg 0x29[7] = 0
I
2
C Addr[0] = 1
Reg 0x29[4] = 0
I
2
C Addr[0] = 1
Reg 0x29[7] = 1
B
O
T
T
O
P
VOUT2
VOUT1
VOUT7
VOUT8
Example Mixed
802.3at, 802.3bt
VOUT3
VOUT5
VOUT4
VOUT6
Figure 1.6. I
2
C Hosted
UG425: Si3474 EVB User's Guide
Kit Description and Powering Up the Si3474 EVB
silabs.com
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