MAX5944 MAXIM [Maxim Integrated Products], MAX5944 Datasheet - Page 12

• Manufacturer Part Number: MAX5944
• Description: Dual FireWire Current Limiter and Low-Drop ORing
• Manufacturer: MAXIM [Maxim Integrated Products]

The MAX5944 dual-channel, independent current-limit
switches have independent ON/OFF control. Both
channels operate from 7.5V to 37V and have default
6.5V undervoltage lockout thresholds. The external
MOSFETs remain off as long as V
V
mable by connecting a resistor-divider at ON_. When
V
5.5V, with respect to OUT_ and the MAX5944 switch
goes into normal operation.
Program the switches’ individual turn-on threshold volt-
ages using the following formula:
where V
channel A and/or B. Choose an R2 value in the 1kΩ
range to minimize error due to ON input bias current.
When operating the MAX5944, ON_ must remain above
its 1.24V threshold. If V
Dual FireWire Current Limiter and Low-Drop
ORing Switch Controller
Figure 5. MAX5944 Power Switch Over ORing Timing Diagram
12
ON_
ON_
______________________________________________________________________________________
< V
> 1.24V and V
V
V
V
I
I
OUT
INA
INA
INB
INB
TURN-ON
ON_REF
R
1
=
. The UVLO thresholds are program-



is the desired turn-on voltage of
V
IN_
TURN ON
ON_
V
1 24
INB
.
> 7.5V, GATE2_ enhances to
> V
Undervoltage Lockout
−
INA
falls below its 1.24V thresh-
−
1



x R
IN_
2
< 6.5V and/or
old, the power-supply MOSFETs turn off immediately
(less than 1µs). This allows the power supply to discon-
nect in the event of a fault condition detected by the
system, such as shorting of the output to a different
power-supply voltage or a FireWire signal pin. If possi-
ble transient conditions exist at the main power-supply
line (IN_), place an RC filter at ON_ to reject transient
voltage dips to prevent unnecessary power-supply
interruptions.
The MAX5944 remain in low-current shutdown mode
when V
shutdown mode disables the channel resulting in less
than 10µA supply current.
FAULT_ are high-voltage, open-drain outputs that pull
low when a current-limit fault shutdown has occurred.
FAULT_ remain low until the next startup cycle.
The MAX5944 autoretry feature attempts to restart after
a t
Figure 6. MAX5944 Operating in Reverse-Current Mode
(Routing Power from Port 1 to Port 2)
OFF
Current-Fault Status Outputs (FAULT_)
of 259ms, limiting the duty cycle of the MOSFETs
ON_
PORT 2
is below the 0.4V threshold. Low-current
30mΩ
ONB
INB
GATE1B
GATE2B
OUTB
SENSEB
MAX5944
Autoretry Fault Management
ONQ1
GND
SENSEA
GATE1A
GATE2A
OUTA
ONA
INA
30mΩ
PORT 1
Q1
Q2