PC7447AMGH1000LB datasheet(17/44 Pages) ATMEL

17 / 44 page

5387B–HIREL–07/05

PC7447A [Preliminary]

Where:

fw = Forward current

s = Saturation current

d = Voltage at diode

f = Voltage forward biased

H = Diode voltage while IH is flowing

L = Diode voltage while IL is flowing

H = Larger diode bias current

L = Smaller diode bias current

q = Charge of electron (1.6 × 10

-19 C)

n = Ideality factor (normally 1.0)

K = Boltzman’s constant (1.38 × 10-23 Joules/K)

T = Temperature (Kelvins)

The ratio of I

H to IL is usually selected to be 10:1. The above simplifies to the following:

H - VL = 1.986 × 10

-4 × nT

Solving for T, the equation becomes:

6.4.4.3

Dynamic Frequency Switching (DFS)

The new DFS feature in the PC7447A adds the ability to divide the processor-to-system bus

ratio by two during normal functional operation by setting the HID1[DFS1] bit. The frequency

change occurs in 1 clock cycle, and no idle waiting period is required to switch between modes.

Additional information regarding DFS can be found in the MPC7450 RISC Microprocessor Fam-

ily User’s Manual.

6.4.4.4

Power Consumption with DFS Enabled

Power consumption with DFS enabled can be approximated using the following formula:

Where:

DFS = Power consumption with DFS enabled

DFS = Core frequency with DFS enabled

f = Core frequency prior to enabling DFS

P = Power consumption prior to enabling DFS (see Table 6-6 on page 19)

DS = Deep sleep mode power consumption (see Table 6-6 on page 19)

The above is an approximation only. Power consumption with DFS enabled is not tested or

guaranteed.

VH V

– L

1 986

–

---------------------------------

PDFS

fDFS

-----------

PPDS

–

()

PDS

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