Datasheet
MAX5943
FireWire Current Limiter and Low-Drop
ORing Switch Controller
18 ______________________________________________________________________________________
Chip Information
TRANSISTOR COUNT: 2324
PROCESS: BiCMOS
SENSE GATE1
OR_ADJ ONQ1GND
MAX5943 EQUIVALENT CIRCUIT
LATCHILIM
FAULT
ON
GATE2 OUT
Q1 Q2
LOAD DISCONNECT
SWITCH
VERY-LOW-DROP
ORing DIODE
CURRENT-LIMIT/CIRCUIT-BREAKER
AND INRUSH CONTROL
IN
TO
FireWire
PORT
FireWire
PORT
SUPPLY
MAX5943A
TIM
R3
+ V
IS
-
R
SENSE
R1
R2
Typical Operating Circuit
PART
CURRENT
LIMITER/
CIRCUIT
BREAKER
DEFAULT
TIMEOUT
(ms)
PROGRAMMABLE
TIMEOUT RANGE
MAX5943A
Current limit
2
1.04ms to 11.05ms
MAX5943B
Circuit breaker
0.5 32.5µs to 345µs
MAX5943C
Circuit breaker
1 65µs to 690µs
MAX5943D
Circuit breaker
2
130µs to 1.38ms
MAX5943E
Circuit breaker
4
260µs to 2.76ms
Selector Guide
30mΩ
SI7958DP SI7958DP
SENSE GATE1
OR_ADJ ONQ1GNDLATCHILIM
FAULT
ON
GATE2 OUT
Q1 Q2
IN
+
-
V
IN
= 12V
TO
FireWire
PORT
FireWire
PORT
SUPPLY
MAX5943A
TIM
4kΩ
10kΩ1kΩ
7.15kΩ
Typical Application Circuit
FireWire Power Management
The MAX5943 serves to regulate and protect FireWire
power over a system interface. The MAX5943 program-
mable features make it suitable for both power provider
and power receiver applications. Figure 14 shows a
high-end two-port FireWire power management system
using two MAX5943As and a dual-channel MAX5944
FireWire current-limiting IC.
Transient Protection
If IN or OUT experiences a fast voltage transient, the
drain-to-gate parasitic capacitance of Q1 and/or Q2
may be sufficient to briefly enhance one of the transis-
tors, allowing current glitch. If the circuit is subjected to
large transients, connect capacitors from the gate to
source across the appropriate MOSFET, preventing the
parasitic capacitance from turning on the device.
Caution: The additional gate-to-source capacitance
causes the turn-off time of the MOSFETs to increase
due to the additional charge of the capacitor. Use the
minimum capacitor value to prevent currents from flow-
ing in hot-plug situations.