MSC7119 datasheet(45/56 Pages) FREESCALE

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Hardware Design Considerations

MSC7119 10/100 Mbps Ethernet MAC Data Sheet, Rev. 6

Freescale Semiconductor

3.3.2

Peripheral Power

Peripherals include the DDR memory controller, Ethernet controller, DMA controller, HDI16, TDM, UART, timers, GPIOs,

and the I

2C module. Basic power consumption by each module is assumed to be the same and is computed by using the

following equation which assumes an effective load of 20 pF, core voltage swing of 1.2 V, and a switching frequency of 100

MHz. This yields:

PPERIPHERAL = 20 pF × (1.2 V)

2 × 150 MHz × 10–3 = 4.32 mW per peripheral

Eqn. 6

Multiply this value by the number of peripherals used in the application to compute the total peripheral power consumption.

3.3.3

External Memory Power

Estimation of power consumption by the DDR memory system is complex. It varies based on overall system signal line usage,

termination and load levels, and switching rates. Because the DDR memory includes terminations external to the MSC7119

device, the 2.5 V power source provides the power for the termination, which is a static value of 16 mA per signal driven high.

The dynamic power is computed, however, using a differential voltage swing of ±0.200 V, yielding a peak-to-peak swing of 0.4

V. The equations for computing the DDR power are:

PDDRIO = PSTATIC + PDYNAMIC

Eqn. 7

PSTATIC = (unused pins × % driven high) × 16 mA × 2.5 V

Eqn. 8

PDYNAMIC = (pin activity value) × 20 pF × (0.4 V)

2 × 300 MHz × 10–3 mW

Eqn. 9

pin activity value = (active data lines

× % activity × % data switching) + (active address lines × % activity)

Eqn. 10

As an example, assume the following:

unused pins = 16 (DDR uses 16-pin mode)

% driven high = 50%

active data lines = 16

% activity = 60%

% data switching = 50%

active address lines = 3

In this example, the DDR memory power consumption is:

PDDRIO = ((16 × 0.5) × 16 × 2.5) + (((16 × 0.6 × 0.5) + (3 × 0.6)) × 20 × (0.4)

× 300 × 10–3) = 326.3 mW

Eqn. 11

3.3.4

External I/O Power

The estimation of the I/O power is similar to the computation of the peripheral power estimates. The power consumption per

signal line is computed assuming a maximum load of 20 pF, a voltage swing of 3.3 V, and a switching frequency of 25 MHz,

which yields:

PIO = 20 pF × (3.3 V)

× 25 MHz × 10–3 = 5.44 mW per I/O line

Eqn. 12

Multiply this number by the number of I/O signal lines used in the application design to compute the total I/O power.

Note:

The signal loading depends on the board routing. For systems using a single DDR device, the load could be as low as

7 pF.

3.3.5

Leakage Power

The leakage power is for all power supplies combined at a specific temperature. The value is temperature dependent. The

observed leakage value at room temperature is 64 mW.

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