Table 3. automatic icut programming – Rainbow Electronics MAX5965B User Manual
Page 21
MAX5965A/MAX5965B
High-Power, Quad, Monolithic, PSE Controllers
for Power over Ethernet
______________________________________________________________________________________
21
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
REGISTER BITS
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
(V
EE
+ 10V) to turn on the MOSFET. An internal 40µA
current source pulls down GATE_ to V
EE
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
GD
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
RS
). A fast pulldown
activates if V
RS
overshoots the limit threshold
(V
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.
Δ
Δ
V
t
I
C
OUT
GATE
GD
=
Figure 3a. Foldback Current Characteristics
48V
28V
V
SU_LIM
V
SU_LIM
/ 3
(V
RS
- V
EE
)
(V
OUT_
- V
EE
)
Figure 3b. Foldback Current Characteristics for High-Power Mode
48V
10V
V
SU_LIM
V
TH_FB
(V
RS
- V
EE
)
(V
OUT_
- V
EE
)