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L9409：Alternator voltage regulator with load response control

The L9409 is a monolithic multifunction alternator voltage regulator intended for use in automotive applications.

The device regulates the output of an automotive generator by controlling the field winding current by means of either an analog fixed frequency PWM signal or digital fixed frequency PWM signal (LRC). The Load Response Control function is activated in order to eliminate IC engine speed fluctuation and vibrations caused by the insertion of sudden electrical loads during alternator low speed operations (f < 310 Hz). Both the analog and digital duty cycle are applied to a high side driver.

The device is able to regulate the voltage either using a feedback signal from B pin or from S pin depending on application needs. S pin is intended to have a clear direct connection with the positive terminal of the car battery. If this connection gets lost the device will regulate voltage using B pin giving a fail safe functionality.

Using L pin is possible to sense key switch and a pre-excitation duty cycle is applied on the field coil in order to start phase voltage sensing. In the case L connection gets lost, device starts to generate using residual magnetism of the generator.

Field, lamp and relay drivers are protected against short circuit.

Key Features

• IC regulator for 12 V type alternator
• Fixed frequency regulation loop
• 130 mΩ high side field driver
• Fail safe device with double sensing of battery voltage (VB and VS)
• Load response control (LRC) function activates after an initial time delay
• Self start function from phase frequency
• “Z” shaped regulation curve compliant with VW specification.
• Key recognition from L input
• Field driver, lamp driver and relay driver short protection
• Complex diagnostics
• Thermal shutdown at 175 °C

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