MAX5980 MAXIM [Maxim Integrated Products], MAX5980 Datasheet - Page 18

• Manufacturer Part Number: MAX5980
• Description: Quad, IEEE 802.3at/af PSE Controller
• Manufacturer: MAXIM [Maxim Integrated Products]

Quad, IEEE 802.3at/af PSE Controller
for Power-over-Ethernet
Figure 1. Detection, Classification, and Port Power-Up Sequence
If the result of the first classification event is Class 0 to 3,
then only a single classification event occurs as shown
in Figure 1. However, if the result is Class 4 (or Class
5), the device will perform a second classification event
as shown in Figure 2. Between the classification cycles,
the device performs a first and second mark event as
required by the IEEE 802.3at standard, forcing a -9.3V
probing voltage at OUT_.
When the device enters a powered state, the t
timer is reset and power is delivered to the PD. PGOOD_
(R10h[7:4], Table 16) is set to 1 when the device
enters the normal power condition. PGOOD_ immedi-
ately resets to 0 whenever the power to the port is turned
off. The power-good change bits, PG_CHG_ (R02h[3:0],
Table 8) are set both when the port powers up and when
it powers down.
18
V
-9.1V
-18V
-54V
OUT_
-4V
0V
- V
AGND
80ms
2-Event PD Classification
150ms
t
DET(1)
Powered State
FAULT
A sense resistor, R
and SVEE_ monitors the load current. Under normal oper-
ating conditions, the voltage across R
never exceeds the current-limit threshold, V
V
circuit regulates the GATE_ voltage, limiting the current
to I
if V
fast pulldown circuit activates to quickly recover from the
current overshoot. During startup, if the current-limit con-
dition persists, when the startup timer, t
the port shuts off, and the TSTART_ bit is set (R08h[3:0]
and R09h[3:0], Table 11).
In the normal powered state, the device checks for
overcurrent conditions as determined by V
t
overcurrent period. The t
FAULT
RSENSE_
150ms
t
DET(2)
LIM
RSENSE_
= V
counter sets the maximum allowed continuous
exceeds V
SU_LIM
exceeds V
/R
SENSE_
SENSE_
t
19ms
CLASS
SU_LIM
SU_LIM
FAULT
, connected between SENSE_
Overcurrent Protection
. During transient conditions,
, an internal current-limiting
by more than 500mV, a
counter increases when
SENSE_
START
(V
, times out,
SU_LIM
CUT
RSENSE_
. The
. If
t
)