Datasheet

LTC1646
16
1646fa
Figure 11. 5V Supply Only Typical Application
Figure 12. BD_SEL# Pushbutton Toggle Switch
APPLICATIO S I FOR ATIO
WUUU
If no 3.3V supply is present, Figure 11 illustrates how the
LTC1646 should be configured. First, 3V
SENSE
(Pin 9) is
connected to 3V
IN
(Pin 8), 3V
OUT
(Pin 7) is connected to
5V
OUT
(Pin 5) and the LTC1646’s 3V
IN
pin is connected
through a diode (BAV16W) to 5V
IN
.
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
and reinsert the CPCI board in order to reset the LTC1646’s
circuit breakers.
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
addition to one or more large-value bulk bypass capacitors
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.
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.
2.7Ω
10Ω
0.007Ω
1k
3V
IN
3V
SENSE
5V
SENSE
GATE 5V
OUT
3V
OUT
5V
IN
5V
IN
0.1µF
0.01µF
IRF7413
5V
OUT
LTC1646
8 9 12 11 10 5 7
6
BAV16W
1646 F11
GND
COMPACT PCI
BACKPLANE
CONNECTOR
(MALE)
COMPACT PCI
CIRCUIT CARD
CONNECTOR
(FEMALE)
GND
5V
LONG
5V
4
3
21
Z1: BZX84C6V2
Z1
BD_SEL#
1k
100Ω
LONG GND
15
6
OFF/ON
LTC1646
GND
V(I/0)
PUSH-
BUTTON
SWITCH
1646 F12
1.2k
COMPACT PCI
BACKPLANE
CONNECTOR
(MALE)
COMPACT PCI
CIRCUIT CARD
CONNECTOR
(FEMALE)