MAX5971AETI+T Maxim Integrated Products, MAX5971AETI+T Datasheet - Page 17

• Manufacturer Part Number: MAX5971AETI+T
• Description: IC CTRLR PD IEEE 802.3AF 28WQFN
• Manufacturer: Maxim Integrated Products
• Type: Power Over Ethernet Controller (PoE)r

Specifications of MAX5971AETI+T

• Applications: Remote Peripherals (Industrial Controls, Cameras, Data Access)
• Internal Switch(s): Yes
• Current Limit: Adjustable
• Voltage - Supply: 32 V ~ 60 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 28-WFQFN Exposed Pad
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

The MAX5971A has an internal sense resistor, R
(see the Simplified Diagram), connected between the
source of the internal MOSFET and V
load current. Under normal operating conditions, the
current through R
threshold I
current-limiting circuit regulates the gate voltage of the
internal MOSFET, limiting the current. During transient
conditions, if I
fast pulldown circuit activates to quickly recover from the
current overshoot.
In the normal powered state, the MAX5971A checks for
overcurrent conditions, as determined by I
of I
continuous overcurrent period. This timer is incremented
both in startup and in normal powered state, but under
different conditions. During startup, the counter increas-
es when I
ered state the counter increases when I
I
drops below I
t
duration overcurrent events. When the counter reaches
Figure 3. Foldback Current Characteristics
CUT
FAULT
LIM
. It decreases at a slower pace when I
. The t
counter allows for detection of repeated short-
RSENSE
Single-Port, 40W, IEEE 802.3af/802.3at PSE
LIM
I
TH_FB
FAULT
I
LIM
RSENSE
LIM
I
. If I
RSENSE
______________________________________________________________________________________
exceeds I
SENSE
or I
RSENSE
counter sets the maximum allowed
CUT
exceeds I
(I
. A slower decrement for the
Overcurrent Protection
RSENSE
LIM
exceeds I
Controller with Integrated MOSFET
, while in the normal pow-
10V
LIM
) never exceeds the
by more than 2A, a
EE
RSENSE
LIM
to monitor the
, an internal
CUT
exceeds
= ~88%
RSENSE
SENSE
27V
the t
For a continuous overstress, a fault occurs exactly after
a period of t
After a power-off due to an overcurrent fault, the t
timer is not immediately reset but starts decrementing.
The MAX5971A allows the port to be powered on only
when the t
an automatic port power duty-cycle protection to the
internal MOSFET to avoid overheating.
In the normal powered state, the I
olds are set automatically according to the classification
result (see Table 2 for classification results based on
detection current, and the Electrical Characteristics table
for the corresponding thresholds). During startup, I
always set to 420mA regardless of the detected class.
During startup and normal operation, an internal circuit
senses the port voltage and reduces the current-limit
value and the overcurrent threshold when (V
V
power dissipation on the internal MOSFET. The current
limit eventually reduces down to I
V
OUT
OUT
FAULT
) < 27V. The foldback function helps to reduce the
) < 10V (see Figure 3).
FAULT
limit, the MAX5971A powers down the port.
FAULT
counter reaches zero. This feature sets
.
TH_FB
Foldback Current
LIM
V
AGND
and I
- V
when (V
OUT
CUT
AGND
AGND
thresh-
FAULT
LIM
17
is
-
-