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參數(shù)資料
| 型號： | 22495 |
| 英文描述： | Implementation of Write Allocate Application Note Mobile AMD-K6 Processor Power Supply Design Application Note |
| 中文描述： | 在寫分配執(zhí)行情況的說明移動應(yīng)用的AMD - K6處理器電源設(shè)計應(yīng)用指南 |
| 文件頁數(shù)： | 35/50頁 |
| 文件大?。?/td> | 1087K |
| 代理商： | 22495 |
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Decoupling and Layout Recommendations
25
22495C/0—May 1999
Mobile AMD-K6
Processor Power Supply Design
lines switch from low to high. A typical PC board trace
impedance appears as 50
during the switching time.
Therefore, the theoretically computed current demand is
I = 3.3 V/50
= 66 mA. If this is multiplied by 64 drivers, the
result is 4.22 A. However, the driver acts as a constant current
source/sink of about 20 mA for the first 200 psec then it
behaves as a 40 mA current source/sink until it is
approximately 1 volt from V
CC3
when driving high, or 1 volt
from ground when driving low. From this point the current
linearly decreases to zero. Thus instead of a maximum of
4.22 A, the current is limited to 64
40 mA = 2.56 A current
demand to charge the bus. Using the same techniques as the
previous core, the bulk decoupling for the I/O can be computed
as follows:
This example assumes a maximum processor I/O current
transient of 2.6A, the voltage tolerance of the processor is less
than 145mV, and the voltage regulator response time is 1
μ
s. A
linear regulator is assumed in this example to have a 1
μ
s
response time.
Using three tantalum capacitors with 100-m
ESR (the parallel
resistance is 33m
) as bulk capacitors, the minimum bulk
capacitance is calculated as:
C
O
≥
((2.6A/(0.145
V – [2.6A
33m
]
))
1
μ
s = 44
μ
F
Three 22
μ
F tantalum capacitors with 100-m
ESR meet this
requirement. However, if the regulator response time is 10
μ
s
then 440
μ
F would be required. It is difficult to find a 22
μ
F
tantalum capacitors with an ESR this low. Therefore, it is
necessary to use a much larger value of capacitance to get this
low of an ESR. Two 470
μ
F, 55 m
ESR parts would meet the
requirement. Three 100
μ
F capacitors with an ESR of 100 m
would also work.
High-Frequency
Decoupling
Inductance is also a concern for the high-frequency decoupling
capacitors. Case size can be a significant factor affecting
capacitor inductance. For example, a 0603 case has
significantly more inductance than a 0612 case. AMD
recommends the 0612, 1206, 0805, and 0603 case in order of
best to worst. Inductance can also be reduced by directly
connecting the capacitor to the power pin of the processor. In
order to minimize its inductance, this trace must be short and as
wide as possible. This technique effectively removes two via
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