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Unstable Vcore after normal startup (EHS6) | Thales IoT Developer Community

June 30, 2014 - 7:04pm, 3107 views

Hi, Currently having issues, i hope someone can offer advice: Simple embedded application EHS6 ASC0 via level converter, Emerg_RST and On Pulled up to VDDLP (Pulled low as required.), GPIO5 switching LED via discrete BJT , Batt(x2)@4.1v, RFout, V180 used for ASC0 pullups on rts and txd. No Other connections... Module starts up ok with 60us high (vddlp) pulse to ON (ON signal remains low afterwards) V180 establishes to 1.8v and Vcore to 1.2v Within 3-4seconds sysloading and systart have been received and the module accepts and actions AT commands (eg ATI, AT+CFUN=4 etc) and appears to be functioning ok At approximately 10 seconds after ON, Vcore drops to somewhere between 1.14 and1.02v Unit still seems to function ok. At approximately 30 seconds after ON, Vcore drops to between 800 - 900 mV and becomes noisy with irregular pulses of 100 - 200mV (like it is trying to re-establish but failing) At this point the module becomes unresponsive to ASC0 input (no echo) and requires either a power cycle or Emerg_Rst to restore operation. The sequence then repeats. (EMERG_RST immediately returns Vcore to 1.2V and the cycle repeats exactly the same) There are no indications (URC etc) that the module is about to stop operation I would add that at each stage of this cycle (after initial power up) current consumption of the module drops (being only in the low mA range anyway) till it returns to almost pre ON current (so it doesn't seem like any sort of load/short) and V180 & VDDLP remain stable. Batt+, ON & Rst also all remain at same/correct values. Do we know what the module would be doing at the times when the Vcore drops occur? (as the timing repeats with same accuracy at 10sec and 30sec) I did wonder if it may be the RF stage starting, but the same behaviour occurs with the module in Airplane Mode Any ideas what could be causing this? Many thanks.