MAX5943DEEE+ Maxim Integrated Products, MAX5943DEEE+ Datasheet - Page 14

• Manufacturer Part Number: MAX5943DEEE+
• Description: IC FIREWIRE CURR LIMITER 16-QSOP
• Manufacturer: Maxim Integrated Products

Specifications of MAX5943DEEE+

• 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

FireWire Current Limiter and Low-Drop
ORing Switch Controller
Drive ONQ1 high to disable the power-supply ORing
function. Disabling the MAX5943 ORing function allows
reverse current flow through the power-supply system.
When ONQ1 is high, GATE1 remains fully enhanced as
long as V
V
rent-limit or circuit-breaker fault condition. The MAX5943
reverse-current flow feature permits a higher voltage
source connected to one port to route power to another
port, as long as the voltage at IN remains above the
minimum 7.5V operating range (see Figure 7).
Figure 7. MAX5943 Operating in Reverse-Current Mode
(Routing Power from Port 1 to Port 2)
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.
14
ON_REF
ON_REF
______________________________________________________________________________________
IN
> 7.5V, GATE2 is enhanced to 5.5V, with respect
TURN_ON
. The turn-on threshold is programmable by
threshold, and the MAX5943 is not in a cur-
IN
Reverse Current Override (ONQ1 = High)
is greater than V
R
ON
ON
ONQ1
TIM
TIM
1
=
ONQ1
ILIM
IN
IN
⎛
⎜
⎝
is the desired turn-on voltage of the
V
TURN ON
LATCH
ILIM
1 24
.
SENSE GATE1
SENSE GATE1
_
Undervoltage Lockout
MAX5943
MAX5943
LATCH
GND
UVLO
−
OR_ADJ
IN
1
GND
⎞
⎟ ×
⎠
, V
> 6.5V and V
ON
GATE2
GATE2
OR_ADJ
R
2
is above the
FAULT
FAULT
OUT
OUT
ON
> 1.24V
PORT1
PORT2
ON
<
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
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.
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.
Figure 8. Setting the MAX5943 Turn-On Voltage
Figure 9. Resetting MAX5943 After a Latched Fault Condition
ON
is below the 0.4V threshold. Low-current
R1
R2
Fault Status Output (FAULT)
R1
R2
V
IN
V
IN
IN
ON
GND
ON
IN
LATCH
ON
GND
MAX5943
falls below its 1.24V thresh-
MAX5943
SD
, allows Q1 and