MAX5943EEEE+T Maxim Integrated Products, MAX5943EEEE+T Datasheet - Page 13

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

Specifications of MAX5943EEEE+T

• 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

Timing accuracy is guaranteed for R
4kΩ to 50kΩ. Large R
reduces timing accuracy. A maximum timeout period is
enforced to prevent arbitrarily long operation in current-
limit/circuit-breaker conditions.
Long durations in current-limit/circuit-breaker mode
may produce excessive heating and electrical stresses
in R
power path. Use component values rated to handle
electrical stresses during the timeout period.
GATE1 controls the MAX5943 ORing function. The
MAX5943 accomplishes a very-low-voltage-drop diode
ORing function using an n-channel power MOSFET, Q1.
Initially, GATE1 is off (ONQ1 = low) and the load current
conducts through the body diode of Q1 (Figure 4).
GATE1 rises to 5.5V above SENSE when V
V
low-voltage drop across its source to drain, reducing volt-
age drop, power dissipation, and heat generation in the
power-supply path created by a traditional diode.
The MAX5943 continuously monitors the load current
by the voltage drop, V
resistor. Q1 turns off rapidly when V
V
Set the MAX5943 ORing threshold (V
OR_ADJ to GND for a 5mV threshold, or to IN for a
10mV threshold, or leave it open for a 7.5mV threshold.
Connect ONQ1 to GND for normal ORing function.
Drive ONQ1 high to force Q1 on, regardless of the load
current condition, as long as the voltages at IN and ON
exceed V
device is not in a current fault shutdown.
When a higher voltage supply is connected at OUT
(Figure 5), the sense voltage drops below the program-
mable ORing threshold. The MAX5943 immediately
turns off Q1, blocking reverse current flow from OUT to
IN. The power is then routed from the higher supply
input to the load (Figure 6).
Figure 4. Q1 Current Path During Inital Startup
OR
OR
V
IN
SENSE
, enhancing Q1. Q1’s low R
minus its hysteresis.
ON
UVLO
, Q1, Q2, and any other components in the
Power-Supply ORing (ONQ1 = Low)
IN
+
R
SENSE
V
and V
IS
______________________________________________________________________________________
GND
-
SENSE
FireWire Current Limiter and Low-Drop
TIM
ON_REF
IS
MAX5943
OR_ADJ
, across the current-sensing
values can be used, which
GATE1
, respectively, and the
DS(ON)
ONQ1
Q1
IS
OR
TIM
GATE2
decreases below
provides a very-
) by connecting
ranging from
Q2
IS
OUT
TO FireWire
exceeds
PORT
ORing Switch Controller
Figure 5. MAX5943 ORing Controller Rerouting Load Current
Figure 6. MAX5943 Power Switch Over ORing Timing Diagram
V
V
INA
INB
FROM
BATTERY
SOURCE
FROM
POWER
SOURCE
V
V
V
I
I
OUT
I
I
INA
INA
INB
INB
INA
INB
= 0
ON
ON
IN
IN
R
R
SENSE
SENSE
GND
GND
SENSE GATE1
SENSE GATE1
V
MAX5943
MAX5943
INB
OR_ADJ
OR_ADJ
> V
INA
ONQ1
ONQ1
GATE2
GATE2
OUT
OUT
V
TO FireWire
PORT
INB
I
LOAD
> V
INA
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