MAX5922AEUI MAXIM [Maxim Integrated Products], MAX5922AEUI Datasheet - Page 16

• Manufacturer Part Number: MAX5922AEUI
• Description: +48V, Single-Port Network Power Switch For Power-Over-LAN
• Manufacturer: MAXIM [Maxim Integrated Products]

+48V, Single-Port Network Power Switch
For Power-Over-LAN
Figure 6. Startup Sequence
output voltage slew rate at the OUT pin to dV
100V/ms (max) and the output-current slew rate out of
the OUT pin to dI
The MAX5922 has an integrated 0.45Ω N-channel
power MOSFET. The MOSFET’s drain is connected to
the DRAIN pin and its source is connected to the OUT
pin. The MAX5922 monitors and provides current-limit
protection to the load at all times. The current limit is
programmable using an external current-sensing resis-
tor connected from IN to DRAIN. To be compatible with
the IEE802.3af standard, use a 0.5Ω ±1%, 50ppm/°C
resistor. The MAX5922 features current-limit foldback
and duty-cycle limit to ensure robust operation during
load-fault and short-circuit conditions (see the
Overcurrent Protection section).
When V
t
typical startup sequence.
After POK is asserted, the MAX5922 activates the zero-
current detection function. This function monitors the
output for an undercurrent condition and eventually
turns off the power to the output if the PD is disconnect-
ed (see the Zero-Current Detection section).
16
POK_HIGH
______________________________________________________________________________________
OUT
, POK goes open drain. Figure 6 shows a
is within 750mV of V
OUT
V
IN
CROSSES UVLO
/dt = 35A/ms (max).
+17.5V
+48V
+4V
+8V
0V
0V
IN
0
for more than
t
DET1
, 88ms
OUT
/dt =
t
100V/ms (max)
DET2
, 88ms
The MAX5922 operates from a +32V to +60V supply
voltage range and has a default UVLO set at +38V
(MAX5922A) or +28V (MAX5922B/MAX5922C). The
UVLO threshold is adjustable using a resistive-divider
connected to the UVLO pin (see Figure 7). When the
input voltage is below the UVLO threshold, all operation
stops and the MOSFET is held off. When the input volt-
age is above the UVLO threshold and EN is high, the
MAX5922 goes into operation. See Figures 2 and 4 for
the operational flow charts.
To adjust the UVLO threshold, connect an external
resistive-divider from IN to UVLO and then from UVLO
to AGND. Use the following equation to calculate the
new UVLO threshold:
V
MAX5922C). The UVLO pin input resistance is 50kΩ
(min), keep the R1 and R2 parallel combination value at
least 20 times smaller than 50kΩ to minimize the new
UVLO threshold error.
REF
is typically 1.38V (MAX5922A) or 1.33V (MAX5922B/
21.3ms
t
CLASS
,
V
t
UVLO TH
POK_HIGH
Undervoltage Lockout (UVLO)
, 88ms
_
=
V
POK (OPEN-DRAIN)
REF



1
t
+
R
R
1
2


