MAX5943 Maxim Integrated Products, MAX5943 Datasheet - Page 15

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

The MAX5943 remains in low-current shutdown mode
when V
shutdown mode disables the MAX5943 resulting in less
than 10µA supply current. Shutdown places all logic
inputs in a high-impedance state allowing the inputs to
be connected to IN without drawing additional current
from the supply. An internal delay, t
Q2 to be turned off before the MAX5943 enters low-
current shutdown mode.
FAULT is a high-voltage open-drain output that pulls low
when a current-limit/circuit-breaker fault shutdown has
occurred. FAULT remains low until the next startup cycle.
The MAX5943 offers either latch or autoretry fault man-
agement configurable by the LATCH input. Connect
LATCH to IN for latch fault management or connect
LATCH to GND for autoretry fault management. In latch
fault management, FAULT latches low, GATE1 and
GATE2 latch off indefinitely. Cycle ON low and then
high to unlatch and restart the MAX5943. However, the
MAX5943 will not enter a startup cycle until t
expired. Figure 9 illustrates a way to reset the MAX5943
after a fault using a pushbutton switch.
In autoretry fault management, the MAX5943_ attempt
to restart after a t
ing the duty cycle of the MOSFETs to 1/129 under con-
tinuous fault conditions. FAULT deasserts every time a
restart attempt is made.
During startup, a large capacitor at OUT may result in a
charging current equivalent to the current limit. Choose a
current-limit timeout that will allow a successful startup.
The timeout can be approximated using the following
equation:
where I
the capacitor at OUT, V
I
C
MAX5943 commences by charging the output capacitor
with 1.5A for approximately 2.7ms. Therefore, the
MAX5943A current-limit timeout period (t
greater than 2.7ms for a successful startup. Otherwise,
the MAX5943A powers up in fault management mode
by exceeding the current-limit timeout period.
LOAD
OUT
is the load current during startup. With IN = 12V,
= 330µF, I
LIMIT
ON
is below the 0.4V threshold. Low-current
is the programmed current limit, C
Applications Information
t
ILIM
OFF
______________________________________________________________________________________
LIMIT
Fault Status Output (FAULT)
>
of 128 x t
FireWire Current Limiter and Low-Drop
I
LIMIT
C
= 1.5A, and I
IN
OUT
Startup Consideration
is the supply voltage, and
−
×
Fault Management
ILIM
I
LOAD
V
IN
(or 128 x t
SD
, allows Q1 and
LOAD
ILIM
MAX5943A
) should be
CB
= 0, the
OFF
OUT
) limit-
has
is
ORing Switch Controller
The MAX5943B–MAX5943E do not control the inrush
current during startup. Inrush current control can be
implemented by placing a resistor and capacitor at
GATE2 (Figure 10) to slowly ramp up the gate voltage,
thus limiting the inrush current. The inrush current can
be approximated using the following formula:
Where I
I
To prevent the MAX5943B–MAX5943E from starting up
in a fault condition set:
Figure 9. Resetting MAX5943 After a Latched Fault Condition
Figure 10. Controlling the MAX5943B–MAX5943E Inrush Current
LOAD
+
V
-
IN
is the load current at startup.
IN
G2U
I
R
INRUSH
SENSE
SENSE GATE1
is GATE2’s 45µA sourcing current and
=
MAX5943B–MAX5943E
Q1
I
INRUSH
R1
R2
C
C
GATE
V
OUT
IN
GND
GATE2
Q2
IN
LATCH
ON
GND
2
<
45µA
×
1kΩ
R
MAX5943
SENSE
MAX5943B–MAX5943E
V
I
G U
TH
C
2
GATE
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+
OUT
I
LOAD
I
C
C
OUT
I
LOAD
LOAD
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