+48V Quad Hot-Swap Controllers For
Power-Over-LAN
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RLYD_ is opposite to that of the MAX5914A. For the
MAX5913A, upon the assertion of the RLYON_ input,
RLYD_ sinks 100mA to DGND. For the MAX5914A, when
RLYON_ is high, an internal 1mA current source pulls up
RLYD_ to V
DD
. A 100mA catch diode is internally con-
nected between RYLD_ and V
RLY
to protect the
MAX5913A/MAX5914A from inductive kicks from the
relay coil. V
RLY
must be connected to the high-side relay
supply voltage.
Programmable Timing, RTIM
An external resistor from RTIM to DGND sets the fre-
quency of the internal oscillator upon which t
O
and the
auto-retry times are based.
Use 2k& to 40k& resistors for R
RTIM
.
t
O
= (R
RTIM
/ 2k&) (6.4ms)
If RTIM is unconnected, an internal resistor sets t
O
to a
nominal 6.4ms.
Auto-Retry and Programmable Duty Cycle
The MAX5913A/MAX5914A feature auto-retry with
adjustable duty cycle. Driving RTRYEN high enables the
auto-retry function. When the switch encounters an over-
current for a period greater than t
O
, the switch is turned
off, and remains off for a t
OFF
programmed by DC, a
three-level input. After the t
OFF
period, the switch is
automatically turned on again. When the port encoun-
ters a continuous overload or short-circuit condition, the
switch turns on and off repeatedly with the on duty cycle
of 1%, 2%, or 4% depending on the DC input state
(Table 2). When RTRYEN is low, the auto-retry is dis-
abled, and a fault condition at the switch turns the
switch off and the switch remains latched off. Driving the
corresponding ON control input low resets the latch.
Pulling ON high to turn on the switch. However, the
MAX5913A/MAX5914A always wait a minimum time,
t
OFF,
before restarting the switch.
Logic Interface and Status Outputs
The MAX5913A/MAX5914A logic interface controls the
device functionality. All the basic control functions for
the four switches are separated. ON_ enables individual
on/off control of each MOSFET (the corresponding relay
must be on to turn on the switch). RLYON_ enables indi-
vidual on/off control of each relay. STAT_ indicates POK
or Port-OC (open circuit) status of each switch. The
other logic pins are common to all four switches. A sin-
gle FAULT output goes low when any of the four chan-
nels is latched off. Driving OCEN high enables the
open-circuit detectors. Driving RTRYEN high enables
the auto-retry function, RTRYEN low enables the switch
latch-off function. DC, a three-level logic input, pro-
grams the duty cycle. The STATOUT input selects the
signal multiplexed at STAT_ outputs (Table 1.). Driving
STATOUT high routes POK status to the STAT_ outputs.
Driving STATOUT low routes Port-OC status to the
STAT_ outputs.
Fault Management
UVLO and Power-OK
The MAX5913A/MAX5914A monitor the V
CC
input voltage
and each switchs current and voltage to determine POK,
overcurrent, or Port-OC status. When V
CC
falls below the
UVLO threshold, FAULT goes low and all four switches
and relays are turned off. When the volage across the
switch is less than 1.5V, the switch is fully on, and if the
switch is not in current limit or open circuit, POK status is
good (high).
Open-Circuit Faults
With the open-circuit detector enabled, when any
switch current falls below the open-circuit detector
threshold current, the open-circuit detector turns off the
switch after a 25.6ms delay, FAULT goes low, and the
Port-OC flag is set for that switch. To clear the switch
latched-off condition, FAULT and Port-OC flags drive
the corresponding ON input low.
PORT_ CONDITION
OCEN
STATOUT
STAT_
Enabled. Switch fully on and not in current limit.
x
H
H
(Power-OK_ is good)
Enabled. Switch in current limit, or V
DS
> 1.5V.
x
H
L
(Power-OK_ is not good)
Enabled. Switch current is less than OC threshold,
port is latched off.
H
L
H
(Port-OC_
, Port current is low or zero)
Enabled. Switch fully on and output current is greater
than OC threshold.
H
L
L
(Port-OC_
, Port current is good)
Disabled.
L
L
L
Table 1. Status Output