L9935 Datasheet E-L9935013TR, L9935, L9935013TR | P16-P18

Functional description L9935

16/29 Doc ID 5198 Rev 10

next data transfer took place. After detection of a short to V

we suggest to turn off the

corresponding bridge to reduce power dissipation for at least 1ms.

5.5 Diagnosis of a short to V

During the short current through the sink transistor will rise more rapidly than under normal

load conditions. Reaching a peak current of 1.5 times the maximum PWM current between

typically 2 µs and 5 µs

after turn on will be detected as a short to V

Detecting a short the low side transistor will try to turn on again the next 7 trigger pulse of

the oscillator.

Simultaneously the error flag will updated on each pulse.

Figure 8. Normal PWM current versus short circuit current and detection of short

to V

Between t

and t

short

the over current detection is totally blanked.

Between t

short

and t

PWM

the current threshold is set to 1.5 times the maximum PWM current

(1.5 times the current of current setting LL).

Overcurrent now will set the error flag.

After t

PWM

the current threshold is the nominal PWM current set by the external resistor.

Exceeding this current will just turn off the sink transistor. This is considered as normal

operation. The error flag is detached from the comparator after t

PWM

so no error flag is set

during normal pulse width modulation.

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1

SHORTTHRESHOLD

ON

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ON

T



T

SHORT

ACTIVATIONOFSHORTTHRESHOLD

ON

T

DELAY

T

07-

ACTIVATIONOF07-THRESHOLD

07-THRESHOLD

07-DETECTION

SIGNALINTERNAL

3HORTDETECTION

SIGNALINTERNAL

%RROR

SHORT

07-

SHORT

07-

SHORT

07-

L9935 Functional description

Doc ID 5198 Rev 10 17/29

5.6 Short from an output to ground

The current through the short will be detected by the protection of the source transistor. The

source transistor will turn off exceeding a current of typically 1.8 A. Minimum overload

detection current is 1.2 A. To obtain proper current regulation (by the sink transistors and not

by source transistor shut down) the maximum current of the PWM regulator should be set to

a maximum value of 1.1 A.

5.7 Diagnosis of a short to ground

Detecting an overload will set an overcurrent error (Error2 = LOW) (bit6). To reset the error

flag a new byte must be written into the interface. (Reset of the error flag takes place at the

rising slope of CSN).

5.8 Shorted load

With a shorted load both, the sink- and the source protection or the PWM alone will

respond. In either case there will be no flyback pulse.

5.9 Diagnosis of a shorted load

Shorting the load two events may take place:

– overload (of the high side transistor) while low side transistor overcurrent is

detected will set the following combinations:

bit6 = LOW

bit7 = HIGH

– overload is marginal. So the low side driver may turn off before overload is

detected. This leads to the combination bit6 = HIGH and bit7 = LOW.

5.10 Open load

An open load will not lead to any flyback pulses. Error detection will take advantage of the

flyback pulse. Missing the flyback pulse after reversing the polarity of a motor winding bit7

will become LOW.

Open load will not be tested in the low current mode (current bits HL) to avoid the risk of

instable diagnosis at low flyback currents. Open load immediately after reset or power down

may on random be detected in the low current mode too. This diagnosis however will not

persist longer than 8 changes of polarity.

We strongly suggest to test open load at a high current mode (combination LL).

While circuit clock speed passes the stepper motor resonant points during

acceleration/deceleration phase, it can happen that flyback energy is temporarily insufficient

for a proper open load detection. Under specific circumstances, pending on motor and load

characteristics, this could lead to sporadic faulty open load error messages despite proper

system operation. The recommended solution is an appropriate software filter approach.

A detailed description is available in the application note AN2378 on www.st.com.

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 V

detection using high resistive motors:

The short to V

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 - -

telegram (550 mA or 900 mA) HH HH

Reverse phase (550 mA or 900 mA) XH HH

Any data XH HH

Any data HH HH

P1-P3 P4-P6 P7-P9 P10-P12 P13-P15 P16-P18 P19-P21 P22-P24 P25-P27 P28-P29

L9935

Mfr. #:

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Manufacturer:

STMicroelectronics

Description:

Motor / Motion / Ignition Controllers & Drivers 2-Ph Stepper Motor

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L9935

L9935

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