L9935 Functional description
Doc ID 5198 Rev 10 15/29
Figure 7. Pulse diagram to explain offset chopping
Using offset chopping the changes of the supply current remain half as large as using non
offset chopping.
Turning off the oscillator for example by shorting pin OSC to ground will hinder turning on of
the bridges anymore after the comparators have generated a turn off signal.
External clocking is possible overdrives the charge and discharge currents of the oscillator
for example with a push pull logic gate. So several devices can be synchronized.
5.3 Protection and diagnosis functions
The L9935 provides several protection functions and error detection functions. Current
limitation usually is customer defined by the external current sense resistors. The current
sensed there is used to regulate the current through the stepper motor windings by pulse
width modulation. This PWM regulation protects the sink transistors. The source transistors
are protected by an internal overcurrent shut down turning off the source transistors in case
of overload.
Overload detection of the source transistor will turn off the bridge and set the corresponding
error flag.
To turn on the bridge again a new byte must be written into the interface. (Rising slope of
CSN resets the overload error flag).
Both bridges use the same flags. To locate which bridge is affected by an error the bridges
can be tested individually (One bridge just is turned off to check for the error in the other
bridge).
5.4 Short from an output to the supply voltage V
S
The current will be limited by the pulse width modulator. The sink transistor will turn off again
after some microseconds. The transistor will periodically be turned on again by the oscillator
8 times. After having detected short 8 times the low side transistor will remain off until the
'!0'03
TURNOFFDELAY
DUETOSLOPE
VELOCITYCONTROL
$)
6
/3#
6
32"
TOTALCURRENTCONSUMPTION
CURRENT
THRESHOLD
CURRENT
THRESHOLD
6
32!
)
63
