L9950 - L9950XP

Application information

Doc ID 10311 Rev 11

21/39

3.5

Overvoltage and under voltage detection

If the power supply voltage VS rises above the overvoltage threshold VSOV OFF (typical

21 V), the outputs OUT1 to OUT11 are switched to high impedance state to protect the load.

When the voltage VS drops below the under voltage threshold VSUV OFF (UV switch OFF

voltage), the output stages are switched to the high impedance to avoid the operation of the

power devices without sufficient gate driving voltage (increased power dissipation). If the

supply voltage VS recovers to normal operating voltage the outputs stages return to the

programmed state (input register 0: bit 20=0).

If the under voltage/overvoltage recovery disable bit is set, the automatic turn-on of the

drivers is deactivated. The microcontroller needs to clear the status bits to reactivate the

drivers. It is recommended to set bit 20 to avoid a possible high current oscillation in case of

a shorted output to GND and low battery voltage.

3.6

Temperature warning and thermal shutdown

If junction temperature rises above Tj TW a temperature warning flag is set and is detectable

via the SPI. If junction temperature increases above the second threshold Tj SD, the thermal

shutdown bit will be set and power DMOS transistors of all output stages are switched off to

protect the device. In order to reactivate the output stages the junction temperature must

decrease below Tj SD - Tj SD HYS and the thermal shutdown bit has to be cleared by the

microcontroller.

3.7

Open-load detection

The open load detection monitors the load current in each activated output stage. If the load

current is below the open load detection threshold for at least 1 ms (tdOL) the corresponding

open load bit is set in the status register. Due to mechanical/electrical inertia of typical loads

a short activation of the outputs (e.g. 3ms) can be used to test the open load status without

changing the mechanical/electrical state of the loads.

3.8

Over load detection

In case of an over-current condition a flag is set in the status register in the same way as

open load detection. If the over-current signal is valid for at least tISC = 32 µs, the over-

current flag is set and the corresponding driver is switched off to reduce the power

dissipation and to protect the integrated circuit. If the over-current recovery bit of the output

is zero the microcontroller has to clear the status bits to reactivate the corresponding driver.