Datasheet

ADSP-2184L/ADSP-2185L/ADSP-2186L/ADSP-2187L
Rev. C | Page 37 of 48 | January 2008
POWER DISSIPATION
To determine total power dissipation in a specific application,
the following equation should be applied for each output:
C ⴛ V
DD
2
ⴛ f
where:
C is load capacitance.
f is the output switching frequency.
Example: In an application where external data memory is used
and no other outputs are active, power dissipation is calculated
as follows:
Assumptions:
• External data memory is accessed every cycle with 50% of
the address pins switching.
• External data memory writes occur every other cycle with
50% of the data pins switching.
• Each address and data pin has a 10 pF total load at the pin.
• Application operates at V
DD
= 3.3 V and t
CK
= 30 ns.
Total Power Dissipation = P
INT
+ (C ⴛV
DD
2
ⴛ f)
where:
P
INT
is the internal power dissipation from Figure 28 through
Figure 31 on Page 39.
(C ⴛ V
DD
2
ⴛ f) is calculated for each output, as in the example in
Table 27.
Table 27. Example Power Dissipation Calculation
1
Parameters No. of Pins × C (pF) × V
DD
2
(V) × f (MHz) PD (mW)
Address, DMS
8103.3
2
33.3 29.0
Data Output, WR
9103.3
2
16.67 16.3
RD
1103.3
2
16.67 1.8
CLKOUT 1 10 3.3
2
33.3 3.6
= 50.7
1
Total power dissipation for this example is P
INT
+ 50.7 mW.