L9963E datasheet(67/184 Pages) STMICROELECTRONICS

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4.11.3

Cell open wire diagnostic

The cell open detection can be performed through the Voltage Conversion Routine and it has been studied to

address several safety issues. Diagnostic strategy depends on the ADC_CROSS_CHECK bit.

4.11.3.1

Cell open with ADC_CROSS_CHECK = 0

If the Cell Terminal Diagnostics step of the Voltage Conversion Routine is executed having programmed

ADC_CROSS_CHECK = 0, then the diagnostic addresses the following failures:

•

RLPF degradation: diagnostic has been implemented to guarantee that low pass filter resistor in series to

the Cx pin is below the critical limit RLPF_OPEN

–

On odd cells, RLPF degradation will cause the assertion of the corresponding CELLx_OPEN flag

–

On even cells, flag assertion depends on the RLPF degradation

◦

A small degradation (RLPF < 24 kΩ typ. with 10 nF CLPF) will only cause the assertion of the

corresponding CELLx_OPEN flag

◦

A huge degradation (RLPF > 24 kΩ typ. with 10 nF CLPF) will cause the assertion of both the

corresponding CELLx_OPEN flag and the lower odd cell CELLx-1_OPEN flag

•

L9963E C1-C14 pin open

•

L9963E C0 pin open or PCB connector open

Diagnostic is present just on enabled cells (VCELLx_EN = 1).

The mechanism used for this detection is based on a diagnostic pull down current (IOPEN_DIAG_CX), which allows

to measure the voltage drop generated on the external RLPF resistance connected in series to Cx pin. If such a

voltage drop is higher than VCxOPEN threshold a Cx open connection is detected.

C0 open diagnostic is performed with a pullup current (IOPEN_DIAG_C0) instead of a pulldown. A dedicated

comparator senses C0 pin voltage and compares it with VCxOPEN. In case V(C0) > VCxOPEN, open detection

occurs.

In case of failure detection on an enabled cell:

•

Corresponding fault flag is set and latched into CELLx_OPEN register;

•

Fault is propagated through the FAULT Line;

•

Voltage conversion routine goes into Configuration Override.

For further details see Section 4.12 Voltage conversion routine.

4.11.3.2

Cell open with ADC_CROSS_CHECK = 1

If the Cell Terminal Diagnostics step of the Voltage Conversion Routine is executed having programmed

ADC_CROSS_CHECK = 1, then the diagnostic addresses the following issues:

•

Failure in the filtering capacitor CLPF causing an excessive leakage from cell;

•

ADC error due to bandgap shift or failure on the conversion path.

The mechanism used for this detection is the same as Cell open with ADC_CROSS_CHECK = 0, except that no

pull-down current is sunk from Cx pin.

For each pair of consecutive cells, the two corresponding ADCs, each of whom is referenced to a different

bandgap, are measuring the voltage drop on the external RLPF.

Since no pull-down current is applied while measurement is on going, the voltage drop on RLPF is expected to be

null, and the two measurement results should match.

If one of the two ADCs is experiencing an issue, or an excessive leakage from the CLPF is causing a voltage

drop on the RLPF, a mismatch in the results occurs. If such a mismatch is greater than VADC_CROSS_FAIL, failure

is detected.

In case of failure detection on an enabled cell:

•

The CELLx_OPEN fault latch will be set for both cells belonging to the pair that failed;

•

Fault is propagated through the FAULT Line;

•

Voltage conversion routine goes into Configuration Override.

For further details see Section 4.12 Voltage conversion routine.

L9963E

Safety and diagnostic features

DS13636 - Rev 12

page 67/184

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