MAX5986A MAXIM [Maxim Integrated Products], MAX5986A Datasheet - Page 11

• 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/MAX5987A include complete interface
functions for a PD to comply with the IEEE 802.3af stan-
dard as a Class 1 PD. The devices provide the detection
and classification signatures using a single external sig-
nature resistor. An integrated MOSFET provides isolation
from the buck converter when the PSE has not applied
power. The MAX5986A/MAX5987A guarantee a leakage
current offset of less than 10µA during the detection
phase. The devices feature power-mode undervoltage-
lockout (UVLO) with wide hysteresis and long deglitch
time to compensate for twisted-pair-cable resistive drop
and to ensure glitch-free transitions between detection,
classification, and power-on/-off modes.
The MAX5986A/MAX5987A operate in three different
modes depending on V
tion mode, classification mode, and power mode. The
device is in detection mode when V
and 10.1V, classification mode when V
12.6V and 20V, and power mode when the input voltage
exceeds V
In detection mode, the MAX5986A/MAX5987A provide
a signature differential resistance to V
tion, the power-sourcing equipment (PSE) applies two
voltages to V
minimum 1V increment. The PSE computes the differ-
ential resistance to ensure the presence of the 24.9kω
signature resistor. Connect the 24.9kω signature resistor
(R
tion. The device applies V
mode, and the V
less than 10µA. The DC offset due to protection diodes
does not significantly affect the signature resistance
measurement.
In classification mode, the MAX5986A/MAX5987A sink
a Class 1 classification current. The PSE applies a clas-
sification voltage between 12.6V and 20V, and measures
the classification current. The MAX5986A/MAX5987A use
the external 24.9kω resistor (R
Powered Devices with Integrated DC-DC Converter
SIG
IEEE 802.3af-Compliant, High-Efficiency, Class 1,
) from RREF to GND for proper signature detec-
ON
.
DD
Classification Mode (12.6V < V
, both between 1.4V and 10.1V with a
DD
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Detection Mode (1.4V < V
offset current due to the device is
Detailed Description
DD
DD
. The three modes are detec-
to RREF when in detection
SIG
) to set the classifica-
Operating Modes
DD
DD
is between 1.4V
PD Interface
DD
. During detec-
DD
is between
DD
< 10.1V)
< 20V)
tion current at 10.5mA. The PSE uses this to determine
the maximum power to deliver. The classification cur-
rent includes current drawn by the supply current of
the device so the total current drawn by the PD is within
the IEEE 802.3af standard. The classification current is
turned off when the device leaves classification mode.
In power mode, the MAX5986A/MAX5987A have the
isolation MOSFET between V
MAX5987A has the buck regulator enabled and the LDO
enabled. The MAX5986A can be in either wake mode,
sleep mode, or ultra-low power mode. The buck regulator
is enabled when the MAX5986A is in wake mode.
The devices enter power mode when V
the undervoltage lockout threshold (V
rises above V
nel isolation MOSFET to connect V
current limit internally set to 49mA (typ). The isolation
MOSFET is fully turned on when V
inrush current is below the inrush limit. Once the isola-
tion MOSFET is fully turned on, the device changes the
current limit to 201mA (typ). The buck converter turns on
100ms after the isolation MOSFET turns on fully.
supply voltage with a turn-on UVLO threshold (V
35.4V/38.7V (typ), and a turn-off UVLO threshold (V
at 31.4V (typ). When the input voltage is above V
the device enters power mode and the internal isolation
MOSFET is turned on. When the input voltage is below
V
converter are off.
The MAX5986A drives an LED, or multiple LEDs in series,
with a maximum LED voltage of 6.5V. In sleep mode and
ultra-low power mode, the LED current is pulse width
modulated with a duty cycle of 25% and the amplitude
is set by R
grammable from 10mA to 20mA using R
the formula:
where R
The MAX5986A/MAX5987A operate with up to a 60V
OFF
MAX5986A/MAX5987A
for more than t
SL
SL
is in kω.
ON
. The LED driver current amplitude is pro-
, the device turns on the internal p-chan-
I
LED
OFF_DLY
= 646/R
LED Driver (MAX5986A)
Undervoltage Lockout
, the MOSFET and the buck
DD
Power Mode (V
SL
CC
and V
(mA)
CC
is near V
to V
ON
CC
SL
DD
DD
). When V
fully on. The
according to
rises above
DD
with inrush
DD
and the
> V
ON
OFF
ON
ON
) at
DD
)
)
,