L9963E datasheet(68/184 Pages) STMICROELECTRONICS

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4.11.4

ADC swap

Failures on the ADCs can be detected by the HardWare Self-Check (HWSC) step of the Voltage Conversion

Routine.

L9963E provides the means to operate a limp home functionality. For each pair of cells, in case one of the two

independent ADC fails, it is still possible to perform a swap of the input MUX, in order to allow the remaining ADC

measuring both cells.

User FW may activate, by means of CROSS_ODD_EVEN_CELL, a swap between the two ADCs of a cell pair,

in order to measure even cells through ADCs dedicated to the odd cells, and vice versa. For instance, if the ADC

assigned to cell Cx (even) fails, the adjacent one assigned to cell Cx-1 (odd) can be exploited to implement the

limp home functionality.

Since one ADC has failed, it is not possible to perform a complete scan of the cells in a single measurement

cycle. User SW must switch to the limp home routine where each scan requires two On-Demand Conversions:

•

The first iteration will be executed having set CROSS_ODD_EVEN_CELL = 0 (default)

–

ADCx measures cell Cx → MCU must discard the result, since ADCx is broken

–

ADCx-1 measures cell Cx-1 → Result is good

•

The second iteration will be executed having set CROSS_ODD_EVEN_CELL = 1 (swap mode)

–

ADCx measures cell Cx-1 → MCU must discard the result, since ADCx is broken

–

ADCx-1 measures cell Cx → Result is good

MCU then merges the results of the first and second iteration to obtain a set of 14 reliable values, that can be

used to:

•

Detect an UV/OV on cells (comparison with threshold must be made by user FW)

•

Get an accurate conversion of cells even if in case of fault on a ADC. This makes State Of Charge

estimation still possible

•

Perform total stack voltage measurement as the sum of cells

When in limp home mode, all the ADC based diagnostics are not guaranteed. Fault tolerant time requirements

can still be met by doubling the sample rate (e.g. switching from 100 ms to 50 ms sample time).

4.11.5

PCB open diagnostic

To detect loss of cell wire at PCB connector, the following procedure must be executed:

Convert even cells with an on-demand conversion.

Enable the diagnostic current (IPD_CB) on even cells by programming PCB_open_en_even_curr = 1.

Wait for a proper settling time TPCB_SET, whose minimum value and the minimum settling time can be

estimated according to the following equation:

TPCB_SET=∆VPCBmax

IPD_CBmin×2CLPF= e.g.

1V100μA×2×10nF=200μs

(8)

Choosing TPCB_SET = TCxOPEN_SET is enough if using TCYCLEADC_000 filter option to convert cells at step 1.

In general, the settling time TPCB_SET should be longer than TSAMPLE_MIN in Table 38.

Convert even cells with an on-demand conversion.

Disable the diagnostic current (IPD_CB) on even cells by programming PCB_open_en_even_curr = 0.

For each cell, evaluate the difference between conversion at step 1 and step 4. If higher than a defined

threshold VPCB_DIFF, the PCB connection to the cell is degraded. The open resistance depends on

VPCB_DIFF according to the following equation:

PCB open resistance evaluation

RPCB_OPEN=VPCB_DIFF

IPD_CB

(9)

For instance, setting VPCB_DIFF = 40 mV allows detecting RPCB_OPEN in the [133-400] Ω range.

Repeat all the previous steps for odd cells, using PCB_open_en_odd_curr to manage the diagnostic

current.

L9963E

Safety and diagnostic features

DS13636 - Rev 12

page 68/184

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