LTC1644IGN Просмотр технического описания (PDF) - Linear Technology
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LTC1644IGN Datasheet PDF : 24 Pages
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LTC1644
APPLICATIO S I FOR ATIO
sinusoidal response whose duration and period is depen-
dent on the resonant circuit parameters. Since the abso-
lute maximum supply voltage of the LTC1644 is 13.2V,
transient protection against 12VIN and VEEIN supply volt-
age spikes and ringing is highly recommended.
In these applications, there are two methods for eliminat-
ing these supply voltage transients: using Zener diodes to
clip the transient to a safe level and snubber networks.
Snubber networks are series RC networks whose time
constants are experimentally determined based on the
board’s parasitic resonant circuits. As a starting point, the
capacitors in these networks are chosen to be 10× to 100×
the power MOSFET’s COSS under bias. The series resistor
is a value determined experimentally and ranges from 1Ω
to 50Ω, depending on the parasitic resonant circuit. Note
5VIN
5V
R1
Q1
3VIN
0.005Ω
IRF7413
3.3V
R3
10Ω
that in all LTC1644 circuit schematics, zener diodes and
snubber networks have been added to the 12VIN and VEEIN
(–12V) supply rail and should be used always. Since the
absolute maximum supply voltage of the LTC1644 is
13.2V, snubber networks are not necessary on the 3VIN or
the 5VIN supply lines. Zener diodes, however, are recom-
mended as these devices provide large-scale transient
protection for the LTC1644 against PCI backplane fault
occurrences. All protection networks should be mounted
very close to the LTC1644’s supply voltage using short
lead lengths to minimize lead inductance. This is shown
schematically in Figures 15 and 16 and a recommended
layout of the transient protection devices around the
LTC1644 is shown in Figure 17.
R2
0.007Ω
Q2
IRF7413
5VOUT
5V
3VOUT
3.3V
R4
10Ω
C1
R5 0.047µF
1k
17
16
15
18
13
14
3
3VIN
3VSENSE GATE 3VOUT 5VIN
5VSENSE
5VOUT
Z3
Z4
LTC1644*
GND
Z3, Z4: 1PMT5.0AT3
8
*ADDITIONAL DETAILS OMITTED FOR CLARITY
1644 F15
Figure 15. Place Transient Protection Devices Close to LTC1644’s 5VIN and 3VIN Pins
12VIN –12VIN
R15
Z1
1Ω
C4
0.01µF
1
2
12VIN VEEIN
LTC1644*
GND
R16
1Ω
Z2
C5
0.01µF
8
Z1, Z2: SMAJ12CA
*ADDITIONAL DETAILS OMITTED FOR CLARITY
1644 F16
Figure 16. Place Transient Protection Devices
Close to LTC1644’s 12VIN and VEEIN Pins
3VIN
5VIN
Z3
Z4
VIAS TO
GND PLANE C5
R14
Z2
LTC1644*
C4
Z1
R13
1644 F17
12VIN
VEEIN
GND
*ADDITIONAL DETAILS OMITTED FOR CLARITY
DRAWING IS NOT TO SCALE!
Figure 17. Recommended Layout for Transient Protection Components
1644f
21
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