Application information

L9954 / L9954XP

20/37

Doc ID 14279 Rev 4

3.5

Overvoltage and undervoltage detection

If the power supply voltage VS rises above the overvoltage threshold VSOV OFF (typical 21

V), the outputs OUT1 to OUT6 are switched to high impedance state to protect the load.

When the voltage VS drops below the undervoltage 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 (register 0: bit 20=0) to normal operating voltage the outputs

stages return to the programmed state after at least 32 µs.

If the undervoltage/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 strongly 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

Charge pump

The charge pump runs under all conditions in normal mode. In standby the charge pump is

out of action.

3.7

Temperature warning and thermal shutdown

If junction temperature rises above Tj TW a temperature warning flag is set after at least 32

µs 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 after at least 32 µs. Temperature

warning flag and thermal shutdown bit are latched and must be cleared by the

microcontroller. The related bit is only cleared if the temperature decreases below the

trigger temperature. If the thermal shutdown bit has been cleared the output stages are

reactivated.

3.8

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.

3.9

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.