User guide

UC864-E/G/WD/WDU Hardware User Guide

1vv0300766a Rev.4

- 03/02/09

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 in transmission for short periods of time (let us

say few minutes) and then remains for quite a long time in idle (let us 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 for 790mA maximum RMS current.

There could even be a simple chip package (no heat sink).

Moreover in 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 790mA (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 UC864-E/G/WD/WDU, you can consider it to be during

transmission 1W max during CSD/VOICE calls and 2W max during class12 GPRS

upload. This generated heat will be mostly conducted to the ground plane under the

UC864-E/G/WD/WDU; you must ensure that your application can dissipate heat

In the WCDMA/HSDPA mode(HSDPA for UC864-E/G only), since UC864-

E/G/WD/WDU emits RF signals continuously during transmission, you must pay

special attention how to dissipate the heat generated.

The current consumption will be up to about 730mA in HSDPA (680mA in

WCDMA/WEDGE) continuously at the maximum TX output power (23dBm). Thus,

you must arrange the PCB area as large as possible under UC864-E/G/WD/WDU

which you will mount. You must mount UC864-E/G/WD /WDU on the large ground

area of your application board and make many ground vias to dissipate the heat.

The peak current consumption in the GSM mode is higher than that in WCDMA.

However, considering the heat sink is more important in case of WCDMA.

As mentioned before, a GSM signal is bursty, thus, the temperature drift is more

insensible than WCDMA. Consequently, if you prescribe the heat dissipation in the

WCDMA mode, you don’t need to think more about the GSM mode.

NOTE:

The average consumption during transmissions depends on the power level at which

the device is requested to transmit via the network. The average current consumption

hence varies significantly.

NOTE:

The thermal design for the Power supply must be made keeping an average

consumption at the max transmitting level during calls of 790mA rms plus 90mA rms

for GPS in tracking mode in UC864-G.