ATR2406_14 Datasheet, PDF (21/26 Pages) ATMEL Corporation – Low-IF 2.4-GHz ISM Transceiver

11. 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 = 240bits (USART connection)
T_{packet_length} = 210µs at 1.152Mbits/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 110µs
If not in use, the handheld device will be in power-down mode with the AVR^® watchdog
timer disabled. The AVR power-down current is typically 1.25µA. 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 1.152Kbits/s
Peak current ATR2406 in RX at 1.152Kbits/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 1.152Kbits/s
42mA
57mA
26mA
5mA
1.25µA
5µA
110µs
30µs
210µs
Amount of Current Needed to Transmit One Packet:
Q1 = (0.005A + 0.026A) × 5030µs = 155µAs (charge up time ATR2406 + AVR internal calculations)
Q2 = (0.005A + 0.026A) × 30µs = 0.93µAs (charge for configuring the ATR2406)
Q3 = (0.005A + 0.026A) × 110µs = 3.41µAs (charge for settling the loop filter)
Q4 = (0.005A + 0.042A) × 210µs = 9.87µAs (charge for transmitting the packet)
Q5 = (0.005A) ´ 250 µs = 1.25µAs (charge for turn around (TX to RX, RX to TX, etc.))
Q6 = (0.005A + 0.026A) × 30µs = 0.93µAs (charge for configuring the ATR2406)
Q7 = (0.005A + 0.026A) × 60µs = 1.86µAs (charge for settling the loop filter)
Q8 = (0.005A + 0.057A) × 50µs = 3.10 µAs (charge until valid data can be received)
Q9 = (0.005A + 0.057A) × 210µs = 13.02µAs (charge for receiving the packet)
Q10 = (0.005A + 0.057A) × 50µs = 3.1µAs (charge for latency before receiving)
ATR2406 [DATASHEET]
21
4779Q–ISM–09/14