Rainbow-electronics MAX5965B Instrukcja Użytkownika Pobierz pdf (Strona 21)

MAX5965A/MAX5965B

High-Power, Quad, Monolithic, PSE Controllers

for Power over Ethernet

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Table 3. Automatic ICUT Programming

CL_DISC

PORT

CLASSIFICATION

RESULT

ENx_CL6 EN_HP_ALL EN_HP_CL6 EN_HP_CL5 EN_HP_CL4

RESULTING ICUT

0 Any X X X X X User programmed

1 1 X X X X X ICUT = 110

1 2 X X X X X ICUT = 111

1 0, 3 X X X X X ICUT = 000

1 4, 5 X 0 X X X ICUT = 000

1 5 X 1 X 1 X ICUT = R24h[6:4]

1 5 X 1 X 0 X ICUT = 000

1 4 X 1 X x 1 ICUT = R24h[6:4]

1 4 X 1 X X 0 ICUT = 000

1 6 or Illegal 0 X X X X —

1 6 or Illegal 1 1 1 X X (See Table 35a)

1 6 or Illegal 1 1 0 X X ICUT = 000

1 6 or Illegal 1 0 X X X ICUT = 000

MOSFET Gate Driver

Connect the gate of the external n-channel MOSFET to

GATE_. An internal 50µA current source pulls GATE_ to

+ 10V) to turn on the MOSFET. An internal 40µA

current source pulls down GATE_ to V

to turn off the

MOSFET.

The pullup and pulldown current controls the maximum

slew rate at the output during turn-on or turn-off. Use

the following equation to set the maximum slew rate:

where C

is the total capacitance between GATE and

DRAIN of the external MOSFET. Current limit and the

capacitive load at the drain control the slew rate during

startup. During current-limit regulation, the

MAX5965A/MAX5965B manipulate the GATE_ voltage

to control the voltage at SENSE_ (V

). A fast pulldown

activates if V

overshoots the limit threshold

SU_LIM

). The fast pulldown current increases with the

amount of overshoot. The maximum fast pulldown cur-

rent is 100mA.

During turn-off, when the GATE voltage reaches a value

lower than 1.2V, a strong pulldown switch is activated

to keep the MOSFET securely off.

OUT GATE

Figure 3a. Foldback Current Characteristics

48V28V

SU_LIM

/ 3

- V

)

OUT_

- V

)

Figure 3b. Foldback Current Characteristics for High-Power Mode

48V10V

SU_LIM

TH_FB

- V

)

OUT_

- V

)

1 2 ... 16 17 18 19 20 21 22 23 24 25 26 ... 51 52

MAX5965A/MAX5965B 1

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