L9779WD datasheet(81/170 Pages) STMICROELECTRONICS

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L9779WD

Functional description

169

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

6.13.3

Diagnosis of CPS [OUT21 to OUT28] 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 MSC - and so resetting the diagnosis registers.

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

diagnosis.

Stepper motor driver ON diagnosis (Output driven by MSC 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 MSC command. The latched fault is cleared by reading the diagnosis data registers via

MSC and so resetting the diagnosis registers.

Over current fault has higher priority over OFF condition faults.

Each Bridge has dedicated fault diagnosis register DIAG_H1, DIAG_H2.

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.

The Faults "DETECTION_RUNNING" & "OPEN LOAD" are latched during the during rise &

fall edge of low-side driver command, if the fault disappeared during these phases the fault

condition is no latched:

–

The FAULT DETECTION RUNNING is no latched, the fault comes back to 0 if the

current becomes higher than open load threshold, before the switch off of low-side

driver.

–

The FAULT OPEN LAOD is no latched, the fault comes back to 0 if the current

becomes higher than open load threshold, before the switch off of low-side driver.

A diagnostic read will clear the “fault detection running” flag. Anyway the diagnostic will

restart.

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