L9959 datasheet(28/49 Pages) STMICROELECTRONICS

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Application information

L9959

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DocID027540 Rev 2

4.2.4

Short to battery (SCB) and short to Ground (SCG)

While the power stages are on, the current through them is monitored. If the output current

reaches the current limit IL, the output is switched off after the blanking time tb. In case the

current reaches the limit IOC during this time, a short to battery (SCB) on low-sides or a short

to ground (SCG) on high-sides is diagnosed, and the affected output driver is switched off

immediately, the not affected one after the time tDF_del.

In order to confirm this error, the outputs are turned on again. If the error is detected for the

second time, it is confirmed but it is still not possible to determine to which of the following

types belongs to:



SCB and SCL



SCG and SCL

To discriminate the fault type, it is necessary to turn outputs on for the third time, and in case

the fault is detected, the diagnosis register (DIA_REG1) is updated consequently and the

device is disabled. Otherwise, the SCG and SCB faults are confirmed only.

Figure 18. Current limiting and short circuit

The three different over-current limits are related to the programmable current limitation,

which can be programmed into the SPI register (Table 33: Configuration register

(CONFIG_REG)). The over-current limits are independent of the resistor at pin CF.

Note:

SCG: Fault Detection works correctly if the following condition is respected: Duty (switch on

time) > Tdon + Slew rate + tDF.

4.2.5

Short circuit over load (SCL)

Short circuit over load (SCL) is diagnosed by a retest sequence after a short to battery

(SCB) or a short to ground (SCG) has been detected and confirmed by a retry on the

switched-on high-side and low-side driver. Then after the time tretest, the opposite driver is

switched off (i.e. the high-side in case of a short to battery on the low-side and vice versa). If

the failure then disappears, a short over load (SCL) is detected.

The error is only entered into the diagnosis register and the device is disabled, if it is

confirmed.

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