MC33771 drains battery pack when not in use!

[stevekahle]

Hi,  If I turn off the FRDM and MC33664 boards controlling the (2) MC33771 in my system when I shut down a vehicle, the MC33771 goes to an Idle Mode which consumes too much power and drains the pack.  Only solution I have found is to add an elaborate power circuit which sees the shutdown and keeps power on the FRDM until it can send a sleep command and then disconnects power.  Isn't there a better way to keep from destroying packs?  Why does the MC33771 go to Idle on loss of communications and not to Sleep?

[alexis]

Hi Steve,

Thanks for sharing the device date code. P3.0 is not shipping yet on evb. Please contact your sale representative or distributor regarding the ordering of P3.0 and documentation.

Best regards,

Alexis

[alexis]

Hi,

The MC33771 is a product under development at August 17th.

On the latest revision of the silicon (so starting from rev 3.0), when there is communication loss (TPL) the device will enter automatically into sleep mode.

Ohter way is to detect the shutdown and turn off  when system is going to by sending a sleep mode command. Any communication between MCU of the battery and  the sytem?

Other way is through  monitoring of the current the battery  using the current sensing of MC33771 allowing  shutdown of the  MC33771 when current is flowing low. Is the MCU  supplied by the battery?

[stevekahle]

Hi Alexis,

I see the 9 character build information code for the MC33771 on the EVB I received in November and the one I received two weeks ago from Freescale (not from a distributor) is the same...CTZG1425A.  I guess Rev 3.0 is not shipping yet?  Do  you know when?

Of the 3 suggestions you mentioned it sounds like 1) is not available yet, 2) requires a special circuit and code to sense shutdown, write sleep commands fast and then shutdown, 3) whenever the vehicle stops voltage updates stop and the display is not valid.

I guess i will have to design for 2) for now.  If I use an interrupt to sense power fail I need to complete in-progress writes to the MC33771s before sending any sleep commands to avoid hanging the bus, timeouts and any other delays.

Steve

[stevekahle]

Hi Alexis,

Excellent modification!  How can I tell what rev. silicon I have, I don't see it marked on the IC.  The most recent board I received (about two weeks ago) has a sticker in the S/N space with Rev X and Rev A1.  My documentation must be old as well, my Operating Mode State Diagram is out of date in a document marked

Rev 1.98 9/2014.  How do I get updated documents?

Thanks,

Steve