L9959S datasheet(26/43 Pages) STMICROELECTRONICS

26 / 43 page

Application information

L9959S, L9959T

26/43

DocID023416 Rev 6

Figure 17. 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 32: Configuration register

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

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 tSCLretest, 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.

4.2.6

Open load (OL)

Open load can either be detected in active mode or while the output drivers are in tri-state

condition, disabled by DIS or /ABE. Open load in active mode is enabled using the OLDA in

the configuration register (CONFIG_REG).

Open load in active mode

The open load condition can only be diagnosed if an inductive load is used. In normal

operation, the output free wheels via the built-in diodes below ground, if the high-side output

driver is switched-off. If the output does not go below ground, an open load is detected.

Open load in inactive mode

In inactive mode the open load condition is detected by applying a pull-down current (IPD) to

both outputs. A pull-up current is generated at one output to compensate these two output

currents. If the pull-up current is in the range of one pull-down current, an open load is

diagnosed. If the load is connected, the pull up current is in the range of the sum of both

pull-down currents. An open load is detected, if the load resistance is above the open load

resistance threshold, no open load is detected, if it is below this threshold (ROL). After the

outputs are disabled, it takes the time tDIAGOL until the open load diagnostic can be enabled.

The open load settling time to reach the correct pull up current is tdiagOL1, the open load filter

time is tdiagOL2.

L9959S Datasheet(PDF) 26 Page - STMicroelectronics