[F A Q] Power supply issue

4 thoughts on “[F A Q] Power supply issue

  1. A:

    After the power on,
    the module responds to AT commands only for few seconds. The status led
    blinks but after about 10 seconds it seems the module switches off
    itself. Why?

     

    Q:

    About 10 seconds after the power-on or the insertion of the PIN code the
    module starts the location update procedure, transmitting its data to
    the network at the highest power level. During this phase the relative
    current peaks can be up to 2A. Therefore the power supply circuit has to
    be designed in order to withstand with these current peaks without big
    voltage drops; this means that both the electrical design and the board
    layout must be designed taking care about this information.
    Refer to the Hardware User Guide for different examples of power supply circuit design.

    1. I’m using a GL865 module. The applied 3,8V regulator is designed for 500 mA max. Bulk caps with total size approx. 500 uF makes that the drop during pulses is limited to 1 V. It is beyond spec, but it works.

      I’d suggest that  having a separate supply for VBATT without voltage drop (assumed that more than approx. 30 mA will not occur),  would make things more tolerant regarding the voltage drop. But it is not specified which voltage difference may be present between VBATT and VBATT_AP.

       

      Note: one possible circuiting would be: a schottky diode from VBATT_PA to VBATT would help keeping VBATT to approx. 3,5V without that large drop when VBATT is decoupled with e.g. 47uF. 

  2. We are using the CE910-Aeris, and have a Vreg supplying 3.6v, capable of about 2A.  This works fine most of the time, however, when in a low RSSI environment, we see spikes at startup at nearly 3A (measured from the CE-910 Supply). This is significantly more than the 2A I’ve seen published elsewhere. Is this related to us using a slightly lower voltage? Are there any FW updates to reduce this?  The 3A is enough to droop the supply until it resets, please let us know your thoughts or options.

           Thank you,

                  Travis Smith

    1. Hi Travis,

      CDMA only designs can have a supply that is capable of just 1A. Telit’s xE910 family requires 2A capable supplies in case you select a module that supports GSM/GPRS. The average current consumption from a CE910-DUAL in max power mode is 750mA. Since, you are seeing 3A when the module is powered on in low RSSI areas, this does not seem correct. Have you been able to ensure that your supply is stable to transient high current pulses? Have you done any comparison testing using a CE910-DUAL Interface Board on our EVK2 setup?

      The FAE team would be willing to do a Schematic and/or Gerber review for you, to see if we notice anything that might contribute to a 3A pull. If you are interested please contact us at TS-Americas@telit.com