8. Typical Applications
251
Tsi308 User Manual
80D4000_MA001_02
Tundra Semiconductor Corporation
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8.3.3
Decoupling
The use of decoupling capacitors on the board is recommended. They should be placed as close
to the package as possible without interfering with the signal routing. This can be implemented
with an array of 0603 or 0402-size capacitors. If the application permits, the capacitors should
be mounted on the back of the board directly under the package.
The best way to select the number of capacitors and their values is through SPICE simulations,
if the circuit model for the power delivery system is available. If the circuit model is not
available, the following guidelines should be used for component selection. There should be at
least eight ceramic capacitors to ground of 0.01 uF or 0.1 uF capacitance - one for each V
LDT
power pin. All capacitors should be of X7R dielectric or better.
8.3.4
Bulk Decoupling
Proper bulk decoupling is required for stable operation of the regulator and to ensure low-power
delivery system impedance at low frequencies. It is recommended that low-ESR ceramic (X5R
dielectric or better), OsCon, or aluminum polymer type capacitors be used for bulk decoupling.
8.3.5
Multiple HyperTransport Links
A single V
LDT
regulator can be used to supply power to two HyperTransport links. The
distance from the regulator to the AS90L10208 package should not exceed 1.5 to 2.0 inches.
This scheme is recommended only for applications where board space is constrained so much
that it is impossible to accommodate individual regulators for each port.
It is important to note that although a single voltage regulator can be used to feed two
independent HyperTransport links, the board routing must consist of two separate traces leading
from the regulator to the package. The traces should be 0.2 inches wide and should run
separately for a minimum length of at least 1.0 inch. The minimum spacing between them
should not be less than 0.1 inch. If these layout recommendations are not followed, significant
coupling can be expected between the V
LDT
links if they are connected to the same regulator.
Regardless of which feeding scheme is used to deliver the power to the AS90L10208, it is
recommended that decoupling capacitors be placed at the point where the traces connect to the
AS90L10208.
Please note that it is not recommended that a single voltage regulator be used to feed more than
two HyperTransport links in any application.
Содержание TSI308
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