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# 5.3 Design considerations

61

Part Blackfin BF533

288 (Vddint = 1.2V, f

# Power Estimate (mW)

CCLK= 500MHz from Blackfin BF53X family data sheet.)

MT9V023 3.3V Linear

320 573 (Power calculated using current drawn by Blackfin and CMOS

# Regulator

sensor.)

Table 5.2 An estimate of the power required by the major components of the system is given in this table and equates to 1181mW.

5.3.4

# Thermal considerations

Using the estimated power required in the previous section, the heat produced by the three main components can be calculated. This calculation will illustrate whether the specified operating temperature of the module given in Chapter 2, i.e. an ambient temperature of between 5 and 35â—¦C will result in the three components exceeding their maximum operat- ing temperatures as given in their datasheets. To determine this the following assumptions are made. The module is assumed to be in a steady state with regard to temperature. This assumption is based on a scenario of constant power input and constant ambient temper- ature. The calculations assume passive cooling. Only the Blackfin DSP, image sensor and linear voltage regulator are considered. It is assumed all other components will dissipate negligible amounts of power and can be ignored.

# First the Blackfin BF533 is considered. The Blackfin BF53x family datasheet [80] gives a

maximum junction temperature of 125â—¦C .

formula for calculating a first order approxi-

m a t i o n o f t h e j u n c t i o n t e m p e r a t u r e b a s e d o n a m b i e n t t e m p e r a t u r e ( T A

), power dissipation

( P D

), a thermal coefficient that varies depending on the chip package type, and air flow

(θJA

) is given in the data sheet. This is

T J = T A + ( θ J A × P D ) .

(5.5)

# The chip package is a 169 BG

package and the assumption is zero air flow leading to

a thermal coefficient from the data sheet of θJA = 22.8â—¦C/W. For the maximum ambient temperature of 35â—¦C (given in the specification in Chapter 2) the junction temperature from

the formula is

TJDSP

= 35 + 22.8 × 228 × 10

3

40â—¦C.

(5.6)

This is well below 125â—¦C .

The

ptina MT9V023 data sheet [78] gives an operating temperature of at most 85â—¦C.

maximum junction temperature is not given in the data sheet and there are not any thermal coefficients given so it can only be assumed that the figure given represents the maximum

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