L9942 datasheet(9/40 Pages) STMICROELECTRONICS

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L9942

Device description

Doc ID 11778 Rev 7

9/40

Device description

2.1

Dual power supply: VS and VCC

The power supply voltage VS supplies the half bridges. An internal charge-pump is used to

drive the highside switches. The logic supply voltage VCC (stabilized) is used for the logic

part and the SPI of the device. Due to the independent logic supply voltage the control and

status information will not be lost, if there are temporary spikes or glitches on the power

supply voltage. In case of power-on (VCC increases from undervoltage to VPOR OFF = 2.60 V,

typical) the circuit is initialized by an internally generated power-on-reset (POR). If the

voltage VCC decreases under the minimum threshold (VPOR ON = 2.3 V, typical), the outputs

are switched to tristate (high impedance) and the internal registers are cleared.

2.2

Standby mode

The EN input has a pull-down resistor. The device is in standby mode if EN input isn't set to

a logic high level. All latched data will be cleared and the inputs and outputs are switched to

high impedance. In the standby mode the current at VS (VCC) is less than 3 µA (1 µA) for

CSN = high (DO in tristate). If EN is set to a logic high level then the device will enter the

active mode. In the active mode the charge pump and the supervisor functions are

activated.

2.3

Diagnostic functions

All diagnostic functions (overload/-current, open load, power supply over-/undervoltage,

temperature warning and thermal shutdown) are internally filtered (tGL = 32 µs, typical) and

the condition has to be valid for a minimum time before the corresponding status bit in the

status registers will be set. The filters are used to improve the noise immunity of the device.

Open load and temperature warning function are intended for information purpose and will

not change the state of the bridge drivers. On contrary, the overload/-current and thermal

shutdown condition will disable the corresponding driver (overload/-current) or all drivers

(thermal shutdown), respectively. The microcontroller has to clear the status bit to reactivate

the bridge driver.

2.4

Overvoltage and undervoltage detection

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

21 V), an overvoltage condition is detected. Programmable by SPI (OVW) the outputs are

switched to high impedance state (default after reset) or the overvoltage bit is set without

switching the outputs to high impedance. When the voltage Vs drops below the under-

voltage threshold VSUV OFF, the outputs are switched to high impedance state to avoid the

operation of the power devices without sufficient gate driving voltage (increased power

dissipation). Error condition is latched and the microcontroller needs to clear the status bits

to reactivate the drivers.

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