L9959 datasheet(29/49 Pages) STMICROELECTRONICS

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L9959

Application information

4.2.6

Open load (OL)

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

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

OLDA in the configuration register (CONFIG_REG).

Open load in active mode

With OLDA = '1', 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. It is possible to enable the filter OLDAFILTER by setting the dedicated bit 4 in

SPECIAL_REG (0 or 40ms). With OLDAFILTER = '1', the open-load will be recheck at the

next PWM cycle and if detected again, the failure will be confirmed in DIAG_REG1 (and

latched).

In case OLDAFILTER is set at '0' (40ms) the recheck will be executed after the filter time

expiration and next PWM pulse. If detected again, the failure will be confirmed (and

latched).

Note:

For Open-load in active mode L9959 works properly in case the duration of the transient

conditions is less than 40msec (Transient condition: function of starting current, ending

current, load electrical parameters, DC MOTOR mechanical characteristics...).

Open load in inactive mode

In inactive mode the open load is independent from the OLDAFILTER status (don't care

condition) and it 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.

4.3

VS-undervoltage

VS is monitored for under-voltage. If VS goes below the VS-undervoltage threshold, the

outputs are switched to tristate after the time tFUV.

4.4

Inverse current at VS

An inverse current of maximum 5 A, which decreases during a period of max 250 ms out of

the device at VS does not lead to any destruction. After the exposure to such an inverse

current the device returns to the specified functionality.

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