BQ76940EVM: Some question about bq76940EVM

Hi Nicky,

Be sure to remind the customer that the BQ76940 EVM can support evaluation of the BQ76940 only such as preparing for control by an MCU, or with the BQ78350-R1 gauge.  Both softwares are shown in the questions, but should not be used in the same configuration.

1. A user might suspect the power supply is dropping with time.  Check the current limit or capability of the supply,  measure the voltage independently of the GUI display.  Also consider the note above, if both the gauge and the external software talk to the BQ76940, bus collisions can occur resulting in the wrong voltage.  The expected result of a bus collision would be bits being low, if voltage were being read it would appear lower.  If a bus collision occurs the BQ78350-R1 spends most of its timeline trying to talk to the BQ76940 and can make the observation consistent although the individual values may vary.

2. Yes, when the power supply is applied or each time it is turned on the part must be booted.

3. The BQ76940 is not capable of operating in a standalone mode, its registers must be loaded each time power is applied.  That might be done by a MCU in a final system.  For evaluation of the BQ76940 on the EVM a file can be prepared and run by the Sequence tool of the GUI, see the user guide and example files.  When operating with the BQ78350-R1 gauge it stores parameters for the settings to load the BQ76940 registers at each power cycle and has periodic checks of those settings. 

Hi Nicky,

Often those type errors occur when the gauge shuts down before BQStudio sends the commands selected. To avoid this be sure to operate the EVM with sufficient voltage and when reducing cell count change the configuration before changing the connections.  See the EVM user guide http://www.ti.com/lit/slvu925 last paragraph of section 6.4.  With the EVM it is easy to simulate a charge current to prevent shutdown by applying a few mV to the SRP test point.  With the charge current the part should stay awake after boot to reprogram or to change the configuration.

If that is not it, please reply.

Hi Nicky,

It seems reasonable, a couple things to check would be the load on the thermistor and the Vgsth of the N-ch FET.  Be sure you can get above 1V with various temperature conditions of interest and voltages of the battery.

Hi Nicky,

The Manual Control Panel is no longer available. The Advanced Comm SMB window can be used to send commands.