MAX5944 MAXIM [Maxim Integrated Products], MAX5944 Datasheet - Page 11

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

When a higher voltage supply is connected at OUTA
(Figure 4), V
MAX5944 immediately turns off Q1A, blocking reverse-
current flow from OUTA to INA. Power is then routed
Figure 2. MAX5944 Current-Limit Timing Diagram
V
V
V
V
V
V
FAULT
GATE1
GATE2
FAULT
GATE1
GATE2
V
V
I
I
OUT
OUT
OUT
OUT
Dual FireWire Current Limiter and Low-Drop
IS
I
LIMIT
drops below the ORing threshold. The
x R
______________________________________________________________________________________
LOAD
I
LIMIT
< t
(a)
ILIM
(b)
x R
LOAD
t
ILIM
I
LIMIT
I
LIMIT
V
IN
ORing Switch Controller
from the higher supply input (INB) to OUTB, and then to
the load (Figure 5).
Drive ONQ1 high to disable the MAX5944 power-sup-
ply ORing. Disabling the MAX5944 ORing function
allows reverse-current flow through the power-supply
system. When ONQ1 is high, GATE1A and GATE1B
remain fully enhanced as long as their respective V
is greater than 7.5V, V
and the channels are not in a current-limit fault condi-
tion. The MAX5944 reverse-current flow feature permits
a higher voltage source connected at Port 1 to be rout-
ed to Port 2, as long as the voltage at both inputs (IN_)
is initially above the minimum 7.5V operating range,
see Figure 6.
Figure 3. Q1 Current Path During Inital Startup
Figure 4. MAX5944 ORing Controller Rerouting Load Current
FROM BATTERY
V
V
SOURCE
INA
INB
V
IN
ON_
ONA
ONQ1
GND
ONB
Reverse-Current Override (ONQ1 = HIGH)
IN_
INB
INA
+
R
30mΩ
30mΩ
SENSE
V
IS
SENSEB GATE1B
SENSEA GATE1A
-
SENSE_
MAX5944
ON_
MAX5944
Q1A
Q1B
GND
is above the 1.24V threshold,
GATE1_
GATE2B OUTB
GATE2A OUTA
Q2A
Q2B
ONQ1
Q1A
GATE2_
V
INB
I
LOAD
> V
Q2A
INA
OUT_
TO
FireWire
PORT
TO FireWire
PORT
IN_
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