Si3400/Si3401

Rev. 0.9

9

Figure 2. Schematic—Class 1 with Isolated 5.0 V Output*

*Note: This is a simplified schematic. See “AN296:

Using the Si3400/01 PoE PD Controller in Isolated and Non-Isolated

Table 8. Components—Class 1 with Isolated 5.0 V Output

Item

Type

Value

Toler.

Rating

Notes

C1

Capacitor

15 µF

20%

100 V

Switcher supply capacitor. Several paral-

lel capacitors are used for lower ESR.

C2

Capacitor

0.1 µF

20%

100 V

PD input supply capacitor.

C3

Capacitor

1100 µF

20%

10 V

Switcher load capacitor. 100 µF in parallel

1000 µF and optional 1 µH inductor for

additional filtering.

C4

Capacitor

15 nF

10%

16 V

Feedback compensation.

C5

Capacitor

220 nF

10%

16 V

Feedback compensation.

C7

Capacitor

0.1 µF

20%

16 V

VDD bypass capacitor.

C8

Capacitor

1 µF

20%

16 V

Isolated mode soft start (tie ISOSSFT to

VDD if this feature is not used).

R1

Resistor

25.5 k

Ω

1%

1/16 W

Detection resistor.

R2

Resistor

4.99 k

Ω

1%

1/16 W

Pull-up resistor.

R3

Resistor

100

Ω

1%

1/16 W

Feedback compensation resistor.

R4

Resistor

10 k

Ω

1%

1/16 W

Feedback compensation resistor.

R5

Resistor

2.05 k

Ω

1%

1/16 W

Pull-up resistor.

R6

Resistor

36.5 k

Ω

1%

1/16 W

Feedback resistor divider.

R7

Resistor

12.1 k

Ω

1%

1/16 W

Feedback resistor divider.

R8

Resistor

127

Ω

1%

1/16 W

Classification resistor.

D1

Diode

10 A

40 V

Schottky diode; part no. PN PDS1040.

D2

Diode

1 A

100 V

Snubber diode (1N4148)

D3

Diode

15 V

9 A

Snubber diode (DFLT15A)

T1

Transformer

40 µH

Coilcraft part number FA2672 (5 V).

PS2911

Optocoupler

TLV431

Voltage reference

C1

Si3400

Si3401

RJ-45

To Ethernet PHY

RCL

RDET

CT1

CT2

SP1

SP2

C2

SWO

C3

D1

R5

R7

R6

PS2911

T1

R2

VDD

EROUT

R1

ISOSSFT

R3

C5

C4

R4

C7

R8

D2

D3

C8