2 thermal design guidelines – Rainbow Electronics GE863-PY User Manual

Page 27

GE863 Hardware User Guide

1vv0300783 Rev.0 - 10/06/08

page 27 of 80

4.5.2 Thermal Design Guidelines

The thermal design for the power supply heat sink should be done with the following specifications:
• Average current consumption during transmission @PWR level max:

500mA

• Average current consumption during transmission @ PWR level min:

100mA

• Average current during Power Saving(AT+CFUN=5):

4mA

• Average current during idle (Power Saving disabled)

24mA

For GE863-GPS only:
• Average GPS section consumption during Power Saving:

1mA

• Average GPS section consumption during Tracking (Power Saving disabled)

60mA

NOTE: The average consumption during transmissions depends on the power level at which the device is requested
to transmit by the network. The average current consumption hence varies significantly.

TIP: The thermal design for the Power supply should be made keeping an average consumption at the max
transmitting level during calls of 500mA rms plus 60mA rms for GPS in tracking mode.

Considering the very low current during idle, especially if Power Saving function is enabled, it is
possible to consider from the thermal point of view that the device absorbs current significantly only
during calls.
If we assume that the device stays into transmission for short periods of time (let's say few minutes)
and then remains for a quite long time in idle (let's say one hour), then the power supply has always
the time to cool down between the calls and the heat sink could be smaller than the calculated one for
500mA maximum RMS current, or even could be the simple chip package (no heat sink).
Moreover in the average network conditions the device is requested to transmit at a lower power level
than the maximum and hence the current consumption will be less than the 500mA, being usually
around 150mA.
For these reasons the thermal design is rarely a concern and the simple ground plane where the
power supply chip is placed can be enough to ensure a good thermal condition and avoid overheating.
For the heat generated by the GE863, you can consider it to be during transmission 1W max during
CSD/VOICE calls and 2W max during class10 GPRS upload.
This generated heat will be mostly conducted to the ground plane under the GE863; you must ensure
that your application can dissipate it.