EM7455 Getting real hot and not its not working

We purchased 200 EM7455 modules for our product. We are experiencing some of the EM745’s getting real hot and now these do not work. We replaced these heated up ones with new modules. The new ones work fine. We have 3 of the 10 that we tested and that do not work after heating up.

Has anyone experienced this? We are using the Spring firmware. The module is screwed in so I don’t think the connector is shorting. My voltage regulator is still working.

Could you issue the following AT commands and reply with the outputs please?

What do you mean that 3 out 10 don’t work after heating up? Will the 3 work when under normal temperature? What is your platform setup, and what is the ambient situation during normal operation?

We are working indoors in a lab. The EM7455 is driven by a debian processor over the USB bus.

One of the EM7455’s was connected over Sprint for about 5 days. The technician said the part was real hot and then the EM7455 would not acquire the correct IP address. Eventually the kernel drivers would not establish the virtual IP device called eth1. Another EM7455’s LED will not light up but the voltage regulator is 3.3VDC.

We used to think the wrong IP address was a Sprint problem but now we think the part is getting damaged when the temperature is getting too hot. The temperature will go down after a reboot. I am running a python thread that reads the temp using AT!PCTEMP. I send a message to the log if the temp > 65.0 degC.

I think I am going to have my EM7455.py thread pull down the EM7455’s Reset pin if the temp exceeds 60 degC. I will wait 10 minutes and then pull up the Reset pin to try it again.

I don’t see how a 3.3VDC device can get so hot. I am not using a EM7455 heat sync because the temp is not hot under normal conditions. We do not send that much data. I have had a controller running I my house for about a month and it never gets hot. It only happens to a few units.

I can send you my schematic if you want. I don’t have any input pins floating. I don’t know what else to try.

Hi @curry-te, is it possible for you to measure the current consumption of the board?

I don’t have a current sensor. I have a voltage regulator that only provides power to the EM7455. I could query the EM7455’s voltage reading (in millivolts). I am not sure how to query the XBeePro’s voltage. The new XBee3 Zigbee has an “AT %V?” command for voltage but I tried that and it does not work. I assume the voltage will drop a few millivolts below nominal when high current is drawn.

Do you know who sells the large EM7455 heat sink that comes with the eval kit?

Do you think the excessive heat is related to the establishing the wrong IP address for eth1?

One possible cause of overheating is the module kept on transmitting max power in a poor network coverage area with very weak signal strength thus stress the PA and causes the overheating. That’s why the asking of AT!GSTATUS? for confirmation.

Other items to look into are the physical antenna connection and the antenna efficiency or VSWR. Or you can try on different carriers’ network such as AT&T and Verizon to see if the same overheating issue would happen. Also have you confirmed if the appropriate Sprint firmware was used for the module?

Thanks tomato, I will monitor these things. Do you know where I can get a few hundred heat sinks for the EM7455?

You should be able to find a lot of heat sink vendors by searching the internet. A Google search for heatsink led me to the following one which populated on top.

By the way, I noticed that you have integrated Zigbee in the product as well. You may also want to make sure that the Zigbee is not the source of the overheating.

Is it possible that one of you Sierra guys can find out where the heat sink is purchased for the eval EM7455 kit? I want my heat sink to fit underneath the part. Not on top. The EM7455 has full copper underneath for the heat to transfer.

Hi @curry-te, poor signal can also affect to temperature of the module. You can check the signal level by AT+CSQ. For the heat sink, you may contact digikey.com to find a suitable pad for your kit.