L99DZ81EP datasheet(31/62 Pages) STMICROELECTRONICS

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L99DZ81EP

Application information

3.5

Overvoltage and undervoltage detection at VS

If the power supply voltage VS rises above the overvoltage threshold VSOV_OFF, the outputs

OUT4 to OUT10 are switched to high impedance state, the charge pump is disabled and the

H-Bridge gate drivers are switched into sink condition to protect the H-bridge and the load.

When the voltage VS drops below the undervoltage threshold VSUV_OFF (UV-switch-OFF

voltage), the output stages are switched to 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 charge pump is switched on

again, the CP_LOW bit is cleared and the output stages return to the programmed state. If

the undervoltage/overvoltage recovery disable bit is set, the automatic turn-on of the drivers

is deactivated.

If the undervoltage/overvoltage recovery disable bit (OV_UV_RD) is set, the microcontroller

needs to clear the status bits to reactivate the drivers. It is recommended to set OV_UV_RD

bit to avoid a possible high current oscillation in case of a shorted output to GND and low

battery voltage.

3.6

Overvoltage and undervoltage detection at VCC

At power-on (VCC increases from undervoltage to VPOROFF) the circuit is initialized by an

internally generated power-on-reset (POR). If the voltage VCC decreases below the low

threshold (VPORON), the outputs are switched to 3-state (high impedance) and the status

registers are cleared. If the voltage at pin VCC increases above the VCC reset high threshold

VVCCRESHU, the device enters the reset state, all outputs are switched off and all internal

registers are cleared. After the voltage at pin VCC has decreased below VVCCRESHL, the

device enters normal operating mode again and the internal registers are reset.

3.7

Temperature warning and shutdown

If the junction temperature rises above the temperature warning threshold (TjTW), a

temperature warning flag is set after the temperature warning filter time (Tjtft) and can be

read via SPI. If the junction temperature increases above the temperature shutdown

threshold (TjTS), the thermal shutdown bit is set and the power transistors of all output

stages are switched off to protect the device after the thermal shutdown filter time. The

gates of the H-Bridge are discharged by the ‘Resistive Low’ mode.

The temperature warning and thermal shutdown flags are latched and must be cleared by

the microcontroller. This is done by a read and clear command on an arbitrary register,

because both bits are part of the global status register.

After these bits have been cleared, the output stages are reactivated. If the temperature is

still above the thermal warning threshold, the thermal warning bit is set after Tjtft. Once this

bit is set and the temperature is above the temperature shutdown threshold, temperature

shutdown is detected after Tjtft and the outputs are switched off. Therefore the minimum

time after which the outputs are switched off after the bits have been cleared in case the

temperature is still above the thermo-shutdown threshold is twice the thermo-warning/-

shutdown filter time Tjtft.

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