Functional description

L9935

18/29

Doc ID 5198 Rev 10

5.10.1

Over temperature pre alarm

Typically 20K before thermal shut down takes place an over temperature pre alarm (bit7 and

bit6 low) takes place. Typically over temperature pre alarm temperature is between 150 °C

and 160 °C.

5.11

Application hints using a high resistive stepper motor

The L9935 was originally targeted on stepper chopping stepper motor application with

typical resistances of 8..12

. Using motors with higher resistance will work too but

diagnosis behavior will slightly change. This paragraph shows the details that should be

taken in account using diagnosis for high resistive motors.

5.11.1

Startup behavior

The device has simple digital filter to avoid triggering diagnosis at a single event that could

be random noise. This digital filter needs 4 chopping pulses to settle. Using a high resistive

motor this chopping does not take place. Instead the digital filter samples each time a

polarity change takes place. So the first three response telegrams after reset may show an

’open load’ error.

H means check for HIGH at the error bits.

X means don’t care because filter is not yet settled.

Using 75 mA chopping immediately after stand by:

The high resistive motor can be forced to chopping operation in the low current range. This

leads to the same behavior as using a low resistive motor.

Short to VS detection using high resistive motors:

The short to VS flag is overwritten each time the chopper comparator responds. Having

detected a short this flag only can be reset by reaching chopping operation or resetting the

circuit (ENN=1). For a high resistive motor this leads to the following consequence: Once a

short to VS is detected the error flag will persist even if the short is removed again until

either a reset (ENN=1) or chopping (for example in 75mA mode) has taken place. We

suggest to return to operation once a short to VS was detected by using the low current

mode to reset the flag.

Table 7.

High and low resistive motor (error bits)

Input data

High resistive motor

(error bits)

Low resistive motor

(error bits)

Standby

-

-

1st telegram (550 mA or 900 mA)

HH

HH

Reverse phase (550 mA or 900 mA)

XH

HH

Reverse phase (550 mA or 900 mA)

XH

HH

Any data

XH

HH

Any data

HH

HH