L9779WD-SPI datasheet(71/141 Pages) STMICROELECTRONICS

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L9779WD-SPI

Functional description

140

6.11.2

Diagnosis of configurable power stages (CPS)

All CPS have fault diagnostic functions:



Short-circuit to battery voltage: (SCB) can be detected if switches are turned on



Short-circuit to ground:

(SCG) can be detected if switches are turned off



Open load:

(OL) can be detected if switches are turned off



Over temperature:

(OT) will be detected with the general thermal

warning(OT2)

Diagnosis is different for configuration as full-bridges or as single power stages. The faults

are coded in different way and are stored in diagnostic registers.

In each configuration the registers can be read via SPI. With the beginning of each read

cycle the registers are cleared automatically.

In each configuration there is one central diagnostic bit F2 for fault occurrence at any output.

6.11.3

Diagnosis of CPS [OUTA to OUTD] when configured as H-bridges

Stepper motor driver OFF diagnosis (output in high impedance state).

In OFF condition Short to GND/Short to VB or Open Load condition is continuously detected

through a deglitch filter Tdgc_off, after Tmask_step masking time to filter ON/ OFF

transition. To avoid false diagnostic due to motor residual movement, the off command (EN

bit=0) must be sent Tsettle time after the last valid on command PWM bit written to 1 (one

couple of HS and LS switched on). A fault longer than deglitch time is latched.

Off state diagnostic fault can be overwritten by on state fault.

Off state fault does not prevent the stepper from switching on. The latched fault is cleared by

reading the diagnosis data registers via SPI - and so resetting the diagnosis registers.

An Off state due to a wrong command sent by SPI interface does not activate the Off

diagnosis.

Stepper motor driver ON diagnosis (Output driven by SPI CONTR_REG bit)

In ON condition when over current fault is detected and validated after digital filtering time

Tdgc_ON, the bridge is turned OFF and the fault is latched. The bridge is turned ON again

by SPI command. The latched fault is cleared by reading the diagnosis data registers via

SPI and so resetting the diagnosis registers.

Over current fault has higher priority over OFF condition faults.

Each Bridge has dedicated fault diagnosis register H1_DIAG, H2_DIAG.

In ON condition if the current in the load current is lower than I_OPEN_LOAD for a time

longer than Tdgc_ol_on, an Open load condition is detected

It could be necessary two steps of the stepper motor operation to detect the real kind of

fault, in this case as first diagnosis the fault is "Fault detection running" and with the next

PWM command it is possible to understand if the fault is an OPEN LOAD or an

OVERCURRENT/SHORT to GND.

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