UPSD3422EB40U6 datasheet(254/300 Pages) STMICROELECTRONICS

254 / 300 page

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PSD module

UPSD3422, UPSD3433, UPSD3434, UPSD3454

254/300

The default state of the Turbo Bit is logic '0,' meaning Turbo mode is on by default (after

power-up and reset conditions) until it is turned off by the 8032 writing to PMMR0.

28.5.57

PLD current consumption

Figure 95 on page 265 and Figure 96 on page 266 (5 V and 3.3 V devices respectively)

show the relationship between PLD current consumption and the composite frequency of all

the transitions on PLD inputs, indicating that a higher input frequency results in higher

current consumption.

Current consumption of the PLDs have a DC component and an AC component. Both need

to be considered when calculating current consumption for a specific PLD design. When

Turbo mode is on, there is a linear relationship between current and frequency, and there is

a substantial DC current component consumed by the PSD module when there are no

transitions on PLD inputs (composite frequency is zero). The magnitude of this DC current

component is directly proportional to how many product terms are used in the equations of

both PLDs. PSDsoft Express generates a “fitter” report that specifies how many product

terms were used in a design out of a total of 186 available product terms. Figure 95 on

page 265 and Figure 96 on page 266 both give two examples, one with 100% of the 186

product terms used, and another with 25% of the 186 product terms used.

28.5.58

Turbo mode current consumption

To determine the AC current component of the specific PLD design with Turbo mode on, the

user will have to interpolate from the graph, given the number of product terms specified in

the fitter report, and the estimated composite frequency of PLD input signal transitions. For

the DC component (y-axis crossing), the user can calculate the number by multiplying the

number of product terms used (from fitter report) times the DC current per product term

specified in the DC specifications for the PSD module. The total PLD current usage is the

sum of its AC and DC components.

28.5.59

Non-turbo mode current consumption

Notice in Figure 95 on page 265 and Figure 96 on page 266 that when Turbo mode is off,

the DC current consumption is “zero” (just standby current) when the composite frequency

of PLD input transitions is zero (no input transitions). Now moving up the frequency axis to

consider the AC current component, current consumption remains considerably less than

Turbo mode until PLD input transitions happen so rapidly that the PLDs do not have time to

latch their outputs and go to standby between the transitions anymore. This is where the

lines converge on the graphs, and current consumption becomes the same for PLD input

transitions at this frequency and higher regardless if Turbo mode is on or off. To determine

the current consumption of the PLDs with Turbo mode off, extrapolate the AC component

from the graph based on number of product terms and input frequency. The only DC

component in non-Turbo mode is the PSD module standby current.

The key to reducing PLD current consumption is to reduce the composite frequency of

transitions on the PLD input bus, moving down the frequency scale on the graphs. One way

to do this is to carefully select which signals are entering PLD inputs, not selecting high

frequency signals if they are not used in PLD equations. Another way is to use PLD

“Blocking Bits” to block certain signals from entering the PLD input bus.

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