ADSP-21065LCSZ-240 Datasheet, PDF(38/44 Page) Analog Devices

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ADSP-21065LCSZ-240 Datasheet, PDF (38/44 Pages) Analog Devices – DSP Microcomputer

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ADSP-21065L

POWER DISSIPATION

Total power dissipation has two components: one due to inter-

nal circuitry and one due to the switching of external output

drivers. Internal power dissipation depends on the sequence in

which instructions execute and the data operands involved. See

IDDIN calculation in Electrical Characteristics section. Internal

power dissipation is calculated this way:

PINT = IDDIN Â¥ VDD

The external component of total power dissipation is caused by

the switching of output pins. Its magnitude depends on:

â the number of output pins that switch during each cycle (O)

â the maximum frequency at which the pins can switch (f)

â the load capacitance of the pins (C)

â the voltage swing of the pins (VDD).

The external component is calculated using:

PEXT = O Â¥ C Â¥ VDD2 Â¥ f

The load capacitance should include the processorâs package

capacitance (CIN). The frequency f includes driving the load

high and then back low. Address and data pins can drive high

and low at a maximum rate of 1/tCK while in SDRAM burst

mode.

Example:

Estimate PEXT with the following assumptions:

â a system with one bank of external memory (32-bit)

â two 1M Â¥ 16 SDRAM chips, each with a control signal load

of 3 pF and a data signal load of 4 pF

â external data writes occur in burst mode, two every 1/tCK

cycles, a potential frequency of 1/tCK cycles/s. Assume 50%

pin switching

â the external SDRAM clock rate is 60 MHz (2/tCK).

The PEXT equation is calculated for each class of pins that can

drive:

Table V. External Power Calculations

Type

# of %

Pins Switching Ø C Ø f

Ø VDD2 = PEXT

Address

MS0

SDWE

11 50

Data

32 50

SDRAM CLK 1 â

Â¥ 10.7

Â¥ 7.7

Â¥ 10.7

Â¥ 30 MHz

Â¥ 10.9 V

= 0.019 W

= 0.000 W

= 0.042 W

= 0.007 W

PEXT = 0.068 W

A typical power consumption can now be calculated for these

conditions by adding a typical internal power dissipation. (IDDIN

see calculation in Electrical Characteristics section):

PTOTAL = PEXT + (IDDIN Â¥ VDD)

Note that the conditions causing a worst-case PEXT differ from

those causing a worst-case PINT. Maximum PINT cannot occur

while 100% of the output pins are switching from all ones (1s)

to all zeros (0s). Note also that it is not common for an appli-

cation to have 100% or even 50% of the outputs switching

simultaneously.

ENVIRONMENTAL CONDITIONS

Thermal Characteristics

The ADSP-21065L is offered in a 208-lead MQFP and a 196-

ball Mini-BGA package.

The ADSP-21065L is specified for a case temperature (TCASE).

To ensure that TCASE is not exceeded, an air flow source may be

used.

TCASE = TAMB + (PD Â¥ qCA)

TCASE = Case temperature (measured on top surface of package)

PD = Power Dissipation in W (this value depends upon the

specific application; a method for calculating PD is

shown under Power Dissipation)

qJC = 7.1âC/W for 208-lead MQFP

qJC = 5.1âC/W for 196-ball Mini-BGA

Airflow

Table VI. Thermal Characteristics (208-Lead MQFP)

(Linear Ft./Min.) 0

qCA (âC/W)

100 200 400 600

17 13

Table VII. 196-Ball Mini-BGA

(Linear Ft./Min.) 0

qCA (âC/W)

200

400

â38â

REV. C

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