IEEE 802.3af/at-Compliant, Powered Device Interface
Controller with Integrated Power MOSFET
12 _____________________________________________________________________________________
Alternatively, the 2EC output also serves as a wall
adapter detection output when the MAX5969D is pow-
ered by an external wall power adapter. See the Wall
Power Adapter Detection and Operation section for more
information.
Power Mode
The MAX5969D enters power mode when V
IN
rises
above the undervoltage lockout threshold (V
ON
). When
V
IN
rises above V
ON
, the MAX5969D turns on the inter-
nal n-channel isolation MOSFET to connect V
SS
to RTN
with inrush current limit internally set to 135mA (typ). The
isolation MOSFET is fully turned on when the voltage at
RTN is near V
SS
and the inrush current is reduced below
the inrush limit. Once the isolation MOSFET is fully turned
on, the MAX5969D changes the current limit to 800mA.
The open-drain power-good output (PG) remains low for
a minimum of t
DELAY
until the power MOSFET fully turns
on to keep the downstream DC-DC converter disabled
during inrush.
Undervoltage Lockout
The MAX5969D operates up to a 60V supply voltage with
a turn-on UVLO threshold (V
ON
) at 35.4V and a turn-off
UVLO threshold (V
OFF
) at 31V. When the input voltage is
above V
ON
, the MAX5969D enters power mode and the
internal MOSFET is turned on. When the input voltage
goes below V
OFF
for more than t
OFF_DLY
, the MOSFET
turns off.
Power-Good Output
An open-drain output (PG) is used to allow disabling
downstream DC-DC converter until the n-channel isola-
tion MOSFET is fully turned on. PG is pulled low to V
SS
for a period of t
DELAY
and until the internal isolation
MOSFET is fully turned on. The PG is also pulled low
during sleep mode and coming out of thermal shutdown.
Thermal-Shutdown Protection
The MAX5969D includes thermal protection from exces-
sive heating. If the junction temperature exceeds the
thermal-shutdown threshold of +140NC, the MAX5969D
turns off the internal power MOSFET, LED driver, and 2EC
current sink. When the junction temperature falls below
+112NC, the devices enter inrush mode and then return
to power mode. Inrush mode ensures the downstream
DC-DC converter is turned off as the internal power
MOSFET is turned on.
Wall Power Adapter Detection
and Operation
For applications where an auxiliary power source such
as a wall power adapter is used to power the PD,
the MAX5969D features wall power adapter detection.
The MAX5969D gives highest priority to the WAD and
smoothly switch the power supply to WAD when it is
detected. Once the input voltage (V
DD
- V
SS
) exceeds
the mark event threshold, the MAX5969D enables wall
adapter detection. The wall power adapter is connected
from WAD to RTN. The MAX5969D detects the wall
power adapter when the voltage from WAD to RTN is
greater than 9V. When a wall power adapter is detected,
the internal n-channel isolation MOSFET turns off, 2EC
current sink turns on, and classification current is dis-
abled if V
IN
is in the classification range.
Applications Information
Operation with 12V Adapter
Layout Procedure
Careful PCB layout is critical to achieve high efficiency
and low EMI. Follow these layout guidelines for optimum
performance:
1) Place the input capacitor, classification resistor, and
transient voltage suppressor as close as possible to
the MAX5969D.
2) Use large SMT component pads for power dissipat-
ing devices such as the MAX5969D and the external
diodes.
3) Use short and wide traces for high-power paths.
4) Use the MAX5969 evaluation kit layout as a reference.
5) Place enough vias in the pad for the EP of the
MAX5969D so that heat generated inside can be
effectively dissipated by the PCB copper. The rec-
ommended spacing for the vias is 1mm to 1.2mm
pitch. The thermal vias should be plated (1oz cop-
per) and have a small barrel diameter (0.3mm to
0.33mm).
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