LTC1646
W U U
U
APPLICATIO S I FOR ATIO
COMPACT PCI COMPACT PCI
BACKPLANE CIRCUIT CARD
CONNECTOR CONNECTOR
(MALE)
(FEMALE)
Z1
0.007Ω
5V
IN
IRF7413
2
1
5V
OUT
5V
3
4
LONG
5V
2.7Ω
10Ω
BAV16W
1k
0.1µF
0.01µF
8
9
SENSE
12
11
10
GATE 5V
5
7
3V 3V
IN
5V
5V
3V
IN
SENSE
OUT OUT
6
GND
GND
LTC1646
Z1: BZX84C6V2
1646 F11
Figure 11. 5V Supply Only Typical Application
If no 3.3V supply is present, Figure 11 illustrates how the
LTC1646 should be configured. First, 3VSENSE (Pin 9) is
connected to 3VIN (Pin 8), 3VOUT (Pin 7) is connected to
5VOUT (Pin 5) and the LTC1646’s 3VIN pin is connected
through a diode (BAV16W) to 5VIN.
Overvoltage Transient Protection
Good engineering practice calls for bypassing the supply
rail of any analog circuit. Bypass capacitors are often
placed at the supply connection of every active device, in
additiontooneormorelarge-valuebulkbypasscapacitors
per supply rail. If power is connected abruptly, the large
bypass capacitors slow the rate of rise of the supply
voltage and heavily damp any parasitic resonance of lead
or PC trace inductance working against the supply bypass
capacitors.
For applications where the BD_SEL# connector pin is
typically grounded on the backplane, the circuit in
Figure 12 allows the LTC1646 to be reset simply by
pressing a pushbutton switch on the CPCI plug-in board.
This arrangement eliminates the requirement to extract
andreinserttheCPCIboardinordertoresettheLTC1646’s
circuit breakers.
The opposite is true for LTC1646 Hot Swap circuits
mounted on plug-in cards. In most cases, there is no
supply bypass capacitor present on the powered 3.3V or
5V side of the MOSFET switch. An abrupt connection,
produced by inserting the board into a backplane connec-
tor, results in a fast rising edge applied on the 3.3V and the
5V line of the LTC1646.
PUSH-
BUTTON
SWITCH
V(I/0)
COMPACT PCI
BACKPLANE
CONNECTOR
(MALE)
COMPACT PCI
CIRCUIT CARD
CONNECTOR
(FEMALE)
1.2k
BD_SEL#
15
6
OFF/ON
1k
100Ω
LTC1646
LONG GND
GND
1646 F12
Figure 12. BD_SEL# Pushbutton Toggle Switch
1646fa
16
Linear [ Linear ]
