Overview of low duty cycle mode

AN4193

6/10

Doc ID 023837 Rev 1

Since in this mode the RX active time can be very short, it may be worthwhile to also take

into account the time to move from the SLEEP state to the RX state, which is in the order of

120 μs.

An equation that approximates the average current consumption in this mode is as follows:

Equation 3

The equation assumes that there is an average current consumption of 9 mA during the

transition from SLEEP to RX.

It is important to understand that this mode also requires some cooperation from the

microcontroller driving the SPIRIT1. In particular, since the RX timeout is stopped upon

detection of an RSSI value above a certain threshold, two cases can occur:

1.

A valid packet is detected and the reception is completed and signaled to the micro

2.

No packet is detected and the SPIRIT1 can stay indefinitely in the RX state

In order to avoid case 2, it is suggested that upon detection of the RSSI signal, the

microcontroller starts a timer and then aborts reception if a valid packet is not received

within a user-defined timeout.

1.1.3

Current consumption figures

A set of measurements have been taken using an LDC cycle of 100 ms and a variable duty

cycle. The values have been taken using an Agilent N6705B DC power analyzer and are

plotted in

Figure 3. The actual values with comparison to predicted values are shown in

Table 4.

Table 3.

RSSI detection time

RX filter min (kHz)

RX filter max (kHz)

RSSI detection time

(µS)

Comment

4.2

7.0

1800

7

7.014.0950

6

14.0

28.0

550

5

28.0

56.1

346

4

56.1

112.3

280

3

112.3

224.7

175

2

224.7

450.9

90

1

450.9

800.1

34

0

RX

consumption_average

120

6

–

t

RX

+

t

LDC_cycle

------------------------------ 9

t

LDC_cycle

t

RX

–

120

6

–

–

t

LDC_cycle

------------------------------------------------------------ 0.00085 mA

⋅

+

⋅

=