L9942 datasheet(11/40 Pages) STMICROELECTRONICS

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L9942

Device description

Doc ID 11778 Rev 7

11/40

slow decay mode always. Otherwise one of the fast decay modes is automatic selected for a

quick decrease of the load current and so it obtains new lower target value.

2.10

Overcurrent detection

The overcurrent detection circuit monitors the load current in each activated output stage. In

HS stage it is in function after detection of current limit during PWM cycle and in LS stage it

works permanently. If the load current exceeds the overcurrent detection threshold for at

least tISC = 4 µs, the overcurrent flag is set and the corresponding driver is switched off to

reduce the power dissipation and to protect the integrated circuit. Error condition is latched

and the microcontroller needs to clear the status bits to reactivate the drivers.

2.11

Open load detection

The open load detection monitors the activity time of the PWM controller and is available for

each phase. If the limit of load current is below around 100mA then open load condition is

detectable. Open load bit for a bridge is set in the register6 if this low current limit can't

reached after at least 15 consecutive PWM cycles.

Truth table shows possible profiles for active open load detection. Maximum threshold IOL is

shown in left column if x bits are 1 (see also Figure 7). Lowest possible limit is e.g. 3.1 mA

for DC2=DC1=DC0=0 and it is set only I0=1.

2.12

Stepping modes

One full revolution can consist of four full steps, eight half steps, sixteen mini steps or 32

microsteps.

Mode is set up in register 0 and it defines increment size of phase counter. Phase counter

value defines address of corresponding current profile. Stepping modes with typical profile

values can see in Figure 3 (e.g. also so called 'Two Phase On' shown in dashed line).

Table 3.

Truth table

DC2

DC1

DC0

max. IOL

0000

xxxx

46mA

0010

xxxx

68mA

01000

52mA

01100

81mA

100000

53mA

101000

78mA

11000001

37mA

11100001

44mA

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