LTC4244 Datasheet, PDF (21/28 Pages) Linear Technology – Rugged, CompactPCI Bus Hot Swap Controllers

LTC4244/LTC4244-1
APPLICATIO S I FOR ATIO
are experimentally determined based on the board’s para-
sitic resonance circuits. As a starting point, the capacitors
in these networks are chosen to be 10× to 100× the power
MOSFET’s C_OSS under bias. The series resistor is a value
determined experimentally that ranges from 1Ω to 50Ω,
depending on the parasitic resonance circuit. Note that in
all LTC4244 circuit schematics, both transient voltage
limiters and snubber networks have been added to the
12V_IN and V_EEIN supply rails and should always be used.
Snubber networks are not necessary on the 3.3V_IN or the
5V_IN supply lines since their absolute maximum voltage
ratings are 13.5V. Transient voltage limiters, however, are
recommended as these devices provide large-scale tran-
sient protection for the LTC4244 in the event of abrupt
changes in supply current. All protection networks should
be mounted very close to the LTC4244’s supply pins using
short lead lengths to minimize trace resistance and induc-
tance. This is shown schematically in Figures 12 and 13
and a recommended layout of the transient protection
devices around the LTC4244 is shown in Figure 14.
R2
Q2
5V_IN
0.007Ω IRF7457
5V_OUT
5V
5V
R1
Q1
3V_IN
0.005Ω
IRF7457
3.3V
3V_OUT
3.3V
R3
10Ω
R4
10Ω
C1
R5 _0.047µF
1k
17
16
15
18
13
14
3.3V_IN 3.3V_SENSE GATE 3.3V_OUT 5V_IN
5V_SENSE
Z3
LTC4244*
GND
Z3, Z4: SMAJ5.0A
8
*ADDITIONAL DETAILS OMITTED FOR CLARITY
3
5V_OUT
Z4
4244 F12
Figure 12. Place Transient Protection Devices Close to LTC4244’s 5V_IN and 3.3V_IN Pins
R13
Z1
10Ω
C4
0.1µF
12V_IN –12V_IN
1
2
12V_IN V_EEIN
LTC4244*
GND
R14
10Ω
Z2
C5
0.1µF
8
Z1, Z2: SMAJ12CA
*ADDITIONAL DETAILS OMITTED FOR CLARITY
4244 F16
Figure 13. Place Transient Protection Devices
Close to LTC4244’s 12V_IN and V_EEIN Pins
3.3V_IN
5V_IN
Z3
VIAS TO
GND PLANE Z1 C5
R14
Z4
LTC4244*
C4
R13
Z1
4244 F14
12V_IN
V_EEIN
GND
*ADDITIONAL DETAILS OMITTED FOR CLARITY
DRAWING IS NOT TO SCALE!
Figure 14. Recommended Layout for Transient Protection
Components
42441f
21