Rainbow Electronics MAX5969B User Manual
Page 11
IEEE 802.3af/at-Compliant, Powered Device Interface
Controllers with
Integrated Power MOSFET
MAX5969A/MAX5969B
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When the MAX5969A/MAX5969B are powered by a Type 2
PSE, the 2-event identification output 2EC asserts low
after the internal isolation n-channel MOSFET is fully
turned on. 2EC current sink is turned off when V
DD
goes
below the UVLO threshold (V
OFF
) and turns on when
V
DD
goes above the UVLO threshold (V
ON
), unless V
DD
goes below V
THR
to reset the latched output of the Type 2
PSE detection flag.
Alternatively, the 2EC output also serves as a wall adapt-
er detection output when the MAX5969A/MAX5969B are
powered by an external wall power adapter. See the Wall
Power Adapter Detection and Operation section for more
information.
Power Mode (Wake Mode)
The MAX5969A/MAX5969B enter power mode when V
IN
rises above the undervoltage lockout threshold (V
ON
).
When V
IN
rises above V
ON
, the MAX5969A/MAX5969B
turn on the internal n-channel isolation MOSFET to con-
nect 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 cur-
rent is reduced below the inrush limit. Once the isolation
MOSFET is fully turned on, the MAX5969A/MAX5969B
change 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 MAX5969A/MAX5969B operate up to a 60V sup-
ply voltage with a turn-on UVLO threshold (V
ON
) at
35.4V/38.6V and a turn-off UVLO threshold (V
OFF
) at 31V.
When the input voltage is above V
ON
, the MAX5969A/
MAX5969B enter 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
when coming out of thermal shutdown.
Thermal-Shutdown Protection
The MAX5969A/MAX5969B include thermal protection
from excessive heating. If the junction temperature
exceeds the thermal-shutdown threshold of +140NC,
the MAX5969A/MAX5969B turn off the internal power
MOSFET and 2EC current sink. When the junction tem-
perature 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 MAX5969A/MAX5969B feature wall power adapter
detection. Once the input voltage (V
DD
- V
SS
) exceeds
the mark event threshold, the MAX5969A/MAX5969B
enable wall adapter detection. The wall power adapt-
er is connected from WAD to RTN. The MAX5969A/
MAX5969B detect 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 disabled if V
IN
is in the clas-
sification range.