MAX5986A MAXIM [Maxim Integrated Products], MAX5986A Datasheet - Page 12

• Manufacturer Part Number: MAX5986A
• Description: IEEE 802.3af-Compliant, High-Efficiency, Class 1,Powered Devices with Integrated DC-DC Converter
• Manufacturer: MAXIM [Maxim Integrated Products]

The MAX5986A features a sleep mode and an ultra-low
power mode in which the internal p-channel isolation
MOSFET is kept on and the buck regulator is off. In sleep
mode, the LED driver output (LED) pulse width modu-
lates the LED current with a 25% duty cycle. The peak
LED current (I
enable sleep mode, apply a falling edge to SL with ULP
disconnected or high impedance. Sleep mode can only
be entered from wake mode.
Ultra-low power mode allows the MAX5986A to reduce
power consumption lower than sleep mode, while main-
taining the power signature of the IEEE standard. The
ultra-low power-mode enable input ULP is internally held
high with a 50kω pullup resistor to the internal 5V bias of
the device. To enable ultra-low power mode, apply a fall-
ing edge to SL with ULP = LOW. Ultra-low power mode
can only be entered from wake mode.
To exit from sleep mode or ultra-low power mode and
resume normal operation, apply a falling edge on the
wake-mode enable input (WK).
If the MAX5986A/MAX5987A die temperature reaches
143°C, an overtemperature fault is generated and the
device shuts down. The die temperature must cool down
below +127°C to remove the overtemperature fault con-
dition. After a thermal shutdown condition clears, the
device is reset.
For applications where an auxiliary power source such
as a wall power adapter is used to power the PD,
the MAX5986A/MAX5987A feature wall power adapter
detection.
The wall power adapter is connected from WAD to
PGND. The MAX5986A/MAX5987A detect the wall power
adapter when the voltage from WAD to PGND is greater
than 8.8V. When a wall power adapter is detected, the
internal isolation MOSFET is turned off, classification cur-
rent is disabled.
Connect the auxiliar power source to WAD, connect a
diode from WAD to V
to V
Powered Devices with Integrated DC-DC Converter
CC
IEEE 802.3af-Compliant, High-Efficiency, Class 1,
. See the typical application circuit in Figure 2.
Sleep and Ultra-Low Power Modes
LED
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) is set by an external resistor R
Thermal-Shutdown Protection
DD
, and connect a diode from WAD
WAD Description
(MAX5986A)
SL
. To
The application circuit must ensure that the auxiliary
power source can provide power to V
means of external diodes. The voltage on V
within the V
ate. To allow operation of the DC-DC converter, the V
and V
edge, while on the falling edge the V
down to 7.3V keeping the DC-DC converter on.
Note: When operating solely with a wall power adapter,
the WAD voltage must be able to meet the condition V
> 8.7V, that likely results in WAD > 9.4V.
An internal voltage regulator provides VDRV to internal
circuitry. The VDRV output is filtered by a 1µF capaci-
tor connected from VDRV to GND. The regulator is for
internal use only and cannot be used to provide power to
external circuits. VDRV can be powered by either V
V
for both PD and buck converter operations.
V
lator if V
increases device efficiency by drawing current from
V
connect AUX directly to V
V
converter’s output has reached its regulation voltage.
A 70V voltage clamp is integrated to protect the internal
circuits from a cable discharge event.
The DC-DC buck converter uses a PWM, peak current-
mode, fixed-frequency control scheme providing an
easy-to-implement architecture without sacrificing a fast
transient response. The buck converter operates in a
wide input voltage range from 8.7V to 60V and supports
up to 3.84W of output power at 1.15A load. The devices
provide a wide array of protection features including
UVLO, overtemperature shutdown, short-circuit protec-
tion with hiccup runaway current limit, cycle-by-cycle
peak current protection, and cycle-by-cycle output over-
voltage protection, for enhanced performance and reli-
ability. A frequency foldback scheme is implemented to
reduce the switching frequency to half at light loads to
increase the efficiency.
AUX
OUT
OUT
DRV
MAX5986A/MAX5987A
Internal Linear Regulator and Back Bias
, depending on V
Cable Discharge Event Protection (CDE)
CC
can be used to back bias the VDRV voltage regu-
source switches from V
instead of V
OUT
voltage must be greater than 8.7V, on the rising
DD
is greater than 4.75V. Back biasing VDRV
voltage range to allow the DC-DC to oper-
DD
. If V
AUX
. The internal regulator is used
OUT
DC-DC Buck Converter
OUT
DD
. In this configuration, the
is used as back bias,
to V
DD
AUX
and V
DD
after the buck
and V
DD
CC
must be
may fall
CC
DD
DD
DD
by
or