turn off delay

due to slope

velocity control

∆I

total current consumption

current

threshold 1

current

threshold 2

D99AT421

Figure 5. Pulse diagram to explain offset chopping.

Using offset chopping the changes of the supply current remain half as large as using non offset chop-

ping.

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 overdriving the charge and discharge currents of the oscillator for example

with a push pull logic gate. So several devices can be synchronized.

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).

Short from an Output to the Supply Voltage VS

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 next data transfer took place. After

detection of a short to VS we suggest to turn off the corresponding bridge to reduce power dissipation

for at least 1ms.

L9935

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