ADSP21MOD980N datasheet(21/42 Pages) AD

21 / 42 page

REV. PrB

6/2001

For current information contact Analog Devices at (800) ANALOGD

ADSP-21mod980N

PRELIMINARY TECHNICAL DATA

POWER DISSIPATION

To determine total power dissipation in a specific applica-

tion, the following equation should be applied for each

output:

C = load capacitance

f = output switching frequency

Example:

In an application where an external host is accessing inter-

nal memory and no other outputs are active, power

dissipation is calculated as follows:

Assumptions:

•

External data memory is accessed every fourth cycle

with 50% of the address pins switching.

•

External data memory writes occur every fourth cycle

with 50% of the data pins switching.

•

Each address and data pin has a 64 pF total load at the

pin.

•

Application operates at V

DDEXT = 3.3 V and tCK = 30 ns.

Total Power Dissipation = P

INT + (C

DDEXT

INT= internal power dissipation from Figure 15

DDEXT

f) is calculated for each output, as in the

example in Table 7.

Total power dissipation for this example is:

PD = P

INT + 222.7 mW

Table 7. Example Power Dissipation Calculation

Parameters

# of Pins

× C (pF)

× V

DDEXT

2 (V)

× f (MHz)

PD (mW)

Address

3.32

18.8

104.8

Data Output, WR

964

3.32

18.8

117.9

222.7

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