AnsweredAssumed Answered

MC33771 Initialization Issue

Question asked by Engineering Department on Oct 10, 2019
Latest reply on Oct 15, 2019 by Engineering Department

We are working on MC33771 and facing following issues

 

  1. New Unit ID written in Initialization Register is valid only for 1Sec
  • After powering On the MC33771, We first write into Initialization register (CID = 0x01, BUS_SW=0)
  • With this new unit ID(0x01), We are able to read or Write any register only if we send the command within 1 Sec
  • If we send any command after 1Sec with unit ID=0x01, we don’t get response from MC33771
  • After 1 Sec we can read the register with unit ID=0x00 only

We want to know:-

  • Is it the valid behavior of MC33771
    • As there is t-sleep time 1024mSec mentioned in datasheet (Device goes in sleep mode without external communication for this period)
    • After device goes in sleep mode, should it get RESET and we have to Initialize by assigning the unit ID again (we observed, it responses to Unit ID=0x00 only after we send any read command after valid wakeup sequence)
  • Is System configuration register 2 (SYS_CFG2) has no control over Unit ID retention
    • As we written DIS_SLEEP bit = 1 (Disable Automatic switch in Sleep mode) and AUTO_SWITCH bit = 0
    • When we read this register after 1 Sec with unit ID = 0x00, we get DIS_SLEEP bit = 1 and AUTO_SWITCH bit = 0, means the written value in this register is intact but unit ID(0x01) get sets to 0x00. (Because it responses to Unit ID=0x00 only)

 

 

  1. Threshold value setting registers also sets to their default values if there is no communication for 1Sec

 

  • After powering On the MC33771, We first write into Initialization register (CID = 0x01, BUS_SW=0)
  • With this new unit ID(0x01), We write DIS_SLEEP bit = 1 and AUTO_SWITCH bit = 0 in SYS_CFG2($04) register and new value 0xD985 in TH_ALL_CT ($4B)
  • We get the same value DIS_SLEEP bit = 1, AUTO_SWITCH bit = 0, and 0xD985 if we read these register within 1 Sec with unit ID= 0x01
  • If we send the command after 1 sec period with unit ID=0x01, MC33771 doesn’t respond
  • After 1 Sec, ith unit ID=0x00, we can read these registers. We get the same data written in SYS_CFG2($04) back but get value 0xD780 instead of previously written value (0xD985) from TH_ALL_CT ($4B).

 

We want to know:-

  • Is it the valid behavior of MC33771
    • If threshold values are getting set to defaults then how safety functions (Over and under voltage detection) will be configured for the required values.

Outcomes