LTC4241IGN#PBF Linear Technology, LTC4241IGN#PBF Datasheet - Page 14

• Manufacturer Part Number: LTC4241IGN#PBF
• Description: IC CTRLR HOTSWAP 3.3V AUX 20SSOP
• Manufacturer: Linear Technology
• Type: Hot-Swap Controllerr

Specifications of LTC4241IGN#PBF

• Applications: PCI, PCI-X
• Internal Switch(s): No
• Voltage - Supply: 3.3V, 5V, ±12V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 20-SSOP (0.154", 3.91mm Width)
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

APPLICATIO S I FOR ATIO
LTC4241
Electronic Circuit Breaker for 3.3V Auxiliary Supply
An electronic circuit breaker is used to protect against
excessive load current and short-circuits on the 3.3V
auxiliary supply. The load current is monitored by placing
a sense resistor R3 between AUXIN and AUXSENSE as
shown in Figure 1. The circuit breaker trip threshold is
50mV and exhibits a response time of 8 s. Unlike the PCI
supplies which use the current foldback limit with circuit
breaker during short-circuits, here the circuit breaker will
trip and immediately pull AUXGATE to ground if the
voltage between AUXIN and AUXSENSE exceeds 50mV for
more than 8 s. The external N-channel transistor is turned
off and FAULT is pulled low. The circuit breaker is reset
when AUXON is cycled low then high, or the AUXIN supply
is cycled. If the circuit breaker feature is not required, the
AUXSENSE pin can be shorted to AUXIN.
The trip current of the circuit breaker is set by:
As a design aid, the trip current for commonly used values
for R3 is given in Table 3.
Table 3. I
If more than 8 s of response time is needed to reject
supply current ripple noise, an external resistor, R
20 and capacitor, C
the AUXSENSE circuit. This will give a delay of 15 s.
14
Table 4. N-Channel Power MOSFET Selection Guide
I
CURRENT
TRIP
RATING
8.0A
3.5A
2.7A
10A
13A
TRIP
= 50mV/R3
R3 ( )
vs R3
0.05
0.06
0.07
0.08
0.09
0.1
PART NUMBER
U
FDN 359AN
Si4412ADY
Si2306DS
Si4410DY
IRF7413
F
, of 1 F (Figure 6) can be added to
U
W
PACKAGE
SOT-23
SOT-23
SO-8
SO-8
SO-8
833mA
714mA
625mA
556mA
500mA
I
TRIP
1A
U
F
, of
V
DS
30V
30V
30V
30V
30V
MAX
Supply Bypass Capacitors
In motherboard applications, large bypass capacitors are
recommended at each of the system power supplies to
minimize supply glitches as a result of board insertion. A
supply bypass capacitor of 100 F at 12V
recommended.
PCB Layout Considerations for the Sense Resistor
For proper circuit breaker operation, 4-wire Kelvin-sense
connections between the sense resistor and the LTC4241’s
5V
and AUXSENSE pins are strongly recommended. The
drawing in Figure 8 illustrates the correct way of making
connections between the LTC4241 and the sense resistor.
PCB layout should be balanced and symmetrical to mini-
mize wiring errors. In addition, the PCB layout for the
sense resistors and the power MOSFETs should include
good thermal management techniques for optimal sense
resistor power dissipation.
Power MOSFET and Sense Resistor Selection
Table 4 lists some available N-channel power MOSFETs .
Table 5 lists some current sense resistors that can be used
with the LTC4241’s circuit breakers. Table 6 lists the
supplier web site addresses for discrete components
mentioned throughout this datasheet.
IN
and 5V
TRACK WIDTH W:
0.03" PER AMPERE
ON 1 OZ COPPER FOIL
V
GS
SENSE
20V
20V
20V
20V
20V
MAX
Figure 8. Making PCB Connections to
the Sense Resistor for the 5V Rail
CURRENT FLOW
FROM SUPPLY
pins, 3V
W
5V
IN
IN
0.024
0.057
0.013
0.011
0.046
R
DS(on)
SENSE RESISTOR
and 3V
SENSE
5V
Fairchild Semiconductor
International Rectifier
SENSE
MANUFACTURER
Vishay-Siliconix
Vishay-Siliconix
Vishay-Siliconix
pins and AUXIN
IN
CURRENT FLOW
TO LOAD
connection is
sn4241 4241f
4241 F08