MAX5943 Maxim Integrated Products, MAX5943 Datasheet - Page 14

• Manufacturer Part Number: MAX5943
• Description: FireWire Current Limiter and Low-Drop ORing Switch Controller
• Manufacturer: Maxim Integrated Products

FireWire Current Limiter and Low-Drop
ORing Switch Controller
Figure 6. MAX5943 Power Switch Over ORing Timing Diagram
The MAX5943 operates from 7.5V to 37V and has a
default 6.5V undervoltage lockout threshold. The external
MOSFETs remain off as long as V
V
connecting a resistor-divider at ON. When V
and V
to OUT and the MAX5943 goes into normal operation.
Program the MAX5943’s turn-on voltage using the fol-
lowing formula:
where V
MAX5943. Choose an R2 value in the 1kΩ range to
minimize error due to the ON bias current.
When operating the MAX5943, ON must remain above
its 1.24V threshold. If V
old, the power-supply MOSFETs (Q1 and Q2) turn off
immediately (less than 1µs). This allows the power sup-
ply to disconnect in the event of a fault condition
14
ON_REF
V
______________________________________________________________________________________
V
V
I
I
OUT
INA
INA
INB
INB
IN
> 7.5V, GATE2 is enhanced to 5.5V, with respect
TURN_ON
. The turn-on threshold is programmable by
R
1
=



is the desired turn-on voltage of the
V
TURN ON
1 24
V
INB
.
ON
> V
_
Undervoltage Lockout
INA
falls below its 1.24V thresh-
−
1
IN

 ×

> 6.5V and V
R
2
ON
> 1.24V
ON
<
detected by the system, such as shorting of the output
to a different power-supply voltage or a FireWire signal
pin. If possible transient conditions exist at the main
power-supply line (IN), place an RC filter at ON to
reject transient voltage dips and to prevent unneces-
sary power-supply interruptions.
Figure 7. MAX5943 Operating in Reverse-Current Mode
(Routing Power from Port 1 to Port 2)
Figure 8. Setting the MAX5943 Turn-On Voltage
ON
ON
ONQ1
TIM
TIM
ONQ1
ILIM
R1
R2
IN
IN
V
IN
LATCH
ILIM
IN
ON
GND
SENSE GATE1
SENSE GATE1
MAX5943
MAX5943
MAX5943
LATCH
GND
OR_ADJ
GND
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GATE2
GATE2
OR_ADJ
FAULT
FAULT
OUT
OUT
PORT1
PORT2