MAX5945 MAXIM [Maxim Integrated Products], MAX5945 Datasheet - Page 16

• Manufacturer Part Number: MAX5945
• Description: Quad Network Power Controller for Power-Over-LAN
• Manufacturer: MAXIM [Maxim Integrated Products]

Quad Network Power Controller
for Power-Over-LAN
Figure 3. PGOOD Timing
16
Figure 2. Detection, Classification, and Power-Up Port
Sequence
OUT_
PGOOD
-18V
-48V
-4V
-9V
______________________________________________________________________________________
POK
0V
0V
80ms
150ms
t
DETI
t
PGOOD
150ms
t
DETII
21.3ms
t
CLASS
t
A sense resistor (R
V
stances, the voltage across R
threshold V
internal current-limiting circuit regulates the GATE volt-
age, limiting the current to I
transient conditions, if the SENSE_ voltage exceeds
V
recover from the current overshoot. During startup, if
the current-limit condition persists, when the startup
timer, t
STRT_FLT_ bit is set. In normal powered state, the
MAX5945 checks for overcurrent conditions as deter-
mined by V
counter sets the maximum allowed continuous
overcurrent period. The t
V
pace when V
decrement for the t
repeated short-duration overcurrents. When the counter
reaches the t
port and asserts the IMAX_FLT_ bit. For a continuous
overstress, a fault latches exactly after a period of
t
t
After power-off due to an overcurrent fault, and if the
RSTR_EN bit is set, the t
reset but starts decrementing at the same slower pace.
The MAX5945 allows the port to be powered on only
when the t
automatic duty-cycle protection to the external MOSFET
to avoid overheating. The duty cycle is programmable
using R16h[6-7].
The MAX5945 continuously flags when the current
exceeds the maximum current allowed for the class as
indicated in the CLASS status register. When class
overcurrent occurs, the MAX5945 sets the IVC bit in
register R09h.
During startup and normal operation, an internal circuit
senses the voltage at OUT_ and reduces the current-
limit value when (V
function helps to reduce the power dissipation on the
FET. The current limit eventually reduces to 1/3 of I
when (V
FAULT
FAULT
SU_LIM
SENSE
EE
, monitors the load current. Under all circum-
. V
is programmable using R16h[2-3] and R28[4-7].
START
OUT
exceeds V
, a fast pulldown circuit activates to quickly
SU_LIM
FAULT
_ - V
SU_LIM
FLT_LIM
FAULT
, times out, the port shuts off and the
SENSE
EE
, is programmable using R27h[4-7].
counter is at zero. This feature sets an
S
FLT_LIM
. If SENSE_ exceeds V
) > 50V (see Figure 4).
FAULT
), connected between SENSE_ and
OUT
limit, the MAX5945 powers off the
= ~88% of V
drops below V
_ - V
FAULT
FAULT
Overcurrent Protection
counter allows for detecting
and decreases at a slower
LIM
EE
counter increases when
timer is not immediately
) > 30V. The foldback
= V
S
Foldback Current
never exceeds the
SU_LIM
SU_LIM
FLT_LIM
. The t
/ R
SU_LIM
. A slower
S
. During
FAULT
, an
LIM