MAX5943EEEE+ Maxim Integrated Products, MAX5943EEEE+ Datasheet - Page 15

• Manufacturer Part Number: MAX5943EEEE+
• Description: IC FIREWIRE CURR LIMITER 16-QSOP
• Manufacturer: Maxim Integrated Products

Specifications of MAX5943EEEE+

• Applications: FireWire® Apps
• Fet Type: N-Channel
• Number Of Outputs: 2
• Internal Switch(s): No
• Delay Time - Off: 100ns
• Voltage - Supply: 7.5 V ~ 37 V
• Current - Supply: 1.3mA
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 16-QSOP
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Delay Time - On: -
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant

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.
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
LOAD
LOAD
OUT
is the load current during startup. With IN = 12V,
is the load current at startup.
= 330µF, I
LIMIT
G2U
I
INRUSH
is GATE2’s 45µA sourcing current and
is the programmed current limit, C
Applications Information
t
ILIM
=
OFF
______________________________________________________________________________________
LIMIT
C
C
GATE
>
of 128 x t
OUT
FireWire Current Limiter and Low-Drop
I
LIMIT
C
= 1.5A, and I
IN
OUT
2
Startup Consideration
is the supply voltage, and
×
−
MAX5943B–MAX5943E
×
Fault Management
I
ILIM
G U
I
LOAD
2
V
IN
(or 128 x t
+
I
LOAD
ILIM
LOAD
MAX5943A
) should be
CB
= 0, the
OFF
OUT
) limit-
has
is
ORing Switch Controller
To prevent the MAX5943B–MAX5943E from starting up
in a fault condition set:
Select a sense resistor that causes the circuit-breaker
voltage drop at a current-limit/circuit-breaker level
above the maximum normal operating current.
Typically, set the overload current at 1.2 to 1.5 times
the full load current.
Choose the sense-resistor power rating to accommodate
an overcurrent condition:
where P
during a current-limit/circuit-breaker fault.
Under short-circuit conditions, it is imperative that the
appropriate sense resistor is utilized. Operating the
MAX5943B–MAX5943E at high input voltages can
cause very large currents during the circuit-breaker
timeout period. The peak current will be limited by the
saturation current of Q2 or the series resistance in the
power path (R
Using a 30mΩ on-resistance MOSFET at GATE1 and
GATE2 and a 30mΩ sense resistor results in a short-cir-
cuit current approximately equal to:
where:
For example, an input voltage of 20V produces a current
at approximately 222A (or I
in the power path for the circuit-breaker timeout period.
Choose an R
dissipation during a short-circuit event.
Figure 10. Controlling the MAX5943B–MAX5943E Inrush Current
+
V
-
IN
Optimizing for Short-Circuit Conditions
IN
RSENSE
R
SENSE
R
SENSE
SENSE GATE1
P
TOTAL
TOTAL
RSENSE
is the power dissipated across R
I
MAX5943B–MAX5943E
Q1
INRUSH
I
SC
capable of handling the high power
).
= R
= 30mΩ + 2 x (30mΩ) = 90mΩ
= V
= I
GND
SENSE
GATE2
Q2
2
IN
LIMIT
SAT
<
45μA
/R
R
1kΩ
TOTAL
SENSE
V
of Q2, whichever is less)
+ 2 x (R
TH
x R
C
GATE
SENSE
Choosing R
OUT
ON
I
)
C
C
OUT
I
LOAD
SENSE
SENSE
LOAD
15