ATR2406_06 Datasheet, PDF (20/25 Pages) ATMEL Corporation – Low-IF 2.4-GHz ISM Transceiver

10. Appendix: Current Calculations for a Remote Control
Assumptions:
Protocol
Channel
Loop filter
Handheld device
Base station device
A data packet consists of 24 bytes.
24 bytes = 240 bits (USART connection)
T_{packet_length} = 210 µs at 1.152 Mbits/s
The system will use five predefined channels for frequency hopping spread
spectrum (FHSS) which gives improved immunity against interferers
Loop filter settling time will be 110 µs
If not in use, the handheld device will be in power-down mode with the AVR’s
watchdog timer disabled. The AVR power-down current is typically 1.25 µA.
If an external voltage regulator is used, additional power-down current has to
be taken into account
The base station will periodically scan all the channels of the used subset.
The base station will stay on one channel for 2 seconds. If the base station
receives a correct packet, an acknowledge will be returned to the handheld
device. The power consumption of the base station device is not
power-sensitive, as this part of the application is normally mains powered
Basic Numbers:
Peak current ATR2406 in TX at 1.152 Kbits/s
Peak current ATR2406 in RX at 1.152 Kbits/s
Peak current ATR2406 with synthesizer running
Current ATmega88 active
Current ATmega88 power down (no WDT)
Current ATmega88 power down (+ WDT)
Loop settling time of ATR2406
Configuration of ATR2406
Time needed for exchanging a packet at 1.152 Kbits/s
42 mA
57 mA
26 mA
5 mA
1.25 µA
5 µA
110 µs
30 µs
210 µs
Amount of Current Needed to Transmit One Packet:
Q1 = (0.005A + 0.026A) × 5030 µs = 155 µAs (charge up time ATR2406 + AVR internal calculations)
Q2 = (0.005A + 0.026A) × 30 µs = 0.93 µAs (charge for configuring the ATR2406)
Q3 = (0.005A + 0.026A) × 110 µs = 3.41 µAs (charge for settling the loop filter)
Q4 = (0.005A + 0.042A) × 210 µs = 9.87 µAs (charge for transmitting the packet)
Q5 = (0.005A) × 250 µs = 1.25 µAs (charge for turn around (TX to RX, RX to TX, etc.))
Q6 = (0.005A + 0.026A) × 30 µs = 0.93 µAs (charge for configuring the ATR2406)
Q7 = (0.005A + 0.026A) × 60 µs = 1.86 µAs (charge for settling the loop filter)
Q8 = (0.005A + 0.057A) × 50 µs = 3.10 µAs (charge until valid data can be received)
Q9 = (0.005A + 0.057A) × 210 µs = 13.02 µAs (charge for receiving the packet)
Q10 = (0.005A + 0.057A) × 50 µs = 3.1 µAs (charge for latency before receiving)
20 ATR2406
4779L–ISM–09/06