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 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