MSP430F5659: VBAK Current Demand for Uninitialized MCU

Sorry, I confused VBAK with VBAT.  Please ignore the original post.   The post should read:

I assemble MSP430 MPU onto circuitry together with small 3 V coin cell connected to VBAT  Possibly a few weeks may pass before I connect DVcc and AVcc and use the bootstrap loader to load and run my embedded software.   During this time the only power on the circuit comes from the 3 V coin cell.  

My embedded software initializes various features of the MPU including the Battery Backup System. After software initialization I see the expected about 1 uA flowing into VBAT with RTC running.  

I sometimes measure very low coin cell voltage (coin cell discharged) immediately prior to loading and running the embedded software.  I suspect that the uninitialized MPU is in a state where it draws substantially more current from the coin cell into VBAT than specified when the Battery Backup System is correctly initialized.

I can not find datasheet statements concerning VBAT current demand in the uninitialized condition.

Can anyone provide an estimate of current demand into VBAT prior to initialization of the Battery Backup System?

Thanks!

Hi Michael,

I suggest connecting to a VCC supply when programming. Otherwise the MCU would run in active mode until it goes into an LPM through the code.

Regards,

Luke

Sorry, I didn't make myself very clear.    Here is maybe a better explanation.

During circuit assembly, besides installing a new MPU,  I install a coin cell battery which connects to VBAT with the intention of someday providing backup power for the RTC.  But I do not at this time actually operate the MPU to  initialize the Battery Backup System and the circuit remains unpowered besides the coin cell.   

At a later time, usually several weeks due to other processing done on the circuit, I connect the normal DVcc, AVcc, load my software via the USB bootstrap loader, and execute my software thus initializing the Battery Backup System.  

So several weeks pass between connection of the coin cell battery to a new (direct out of the box) MPU and initialization of the Battery Backup System.

So my question is what is the current demand into VBAT during the time between installation of the coin cell and the point where I initialize the Battery Backup System?

I seek the answer since I sometimes observe that unusual discharge of the coin cell has occurred by the time I load software and initialize the Battery Backup System.  I suspect that a completely uninitialized (direct from TI - right out of the box) is in a state where unusual VBAT current demand occurs.  Maybe someone knows current demand on VBAT in this condition?

Thanks for response!

Hi Michael,

I'm looking into this for you. Just to reconfirm. The device is unprogrammed but is getting set in the system with the battery in place. Then power is applied to the board and the board is programmed, once the MCU is running it correctly initializes the battery backup system. You want to know what current/power the board will draw from the battery before the initialization of the device?

Regards,

Luke