22 I/O MSDI Programmable Current Analog Mux

Designed to operate 4.5 V ≤ VBATP ≤ 36 V, the NXP MC33978 is a multiple switch detection interface (MSDI) . The switch status, either open or closed, is transferred to the microprocessor through a SPI in automotive environments. This SMARTMOS device also features a 24-to-1 analog multiplexer for reading the input channels as analog inputs. The analog selected input signal is buffered and provided on the AMUX output pin for the MCU to read. Independent programmable wetting currents are available as needed for the application. A battery and temperature monitor are included in the IC and available via the AMUX pin.

The 33978 device has two modes of operation, Normal and Low-power mode(LPM). Normal mode allows programming of the device and supplies switch contacts with pull-up or pull-down current as it monitors the change of state on the switches. The LPM provides low quiescent current, which makes the 33978 ideal for automotive and industrial products requiring low sleep-state currents.

Simplified Application Diagram

Simplified Application Diagram

Why Used

  • Operating switch input voltage range from -1.0 V to 36 V
  • Eight programmable inputs (switches to battery or ground)
  • 14 switch-to-ground inputs
  • Selectable wetting current (2, 6, 8, 10, 12, 14, 16, or 20 mA)
  • Interfaces directly to an MCU using 3.3 V / 5.0 V SPI protocol

Where Used

  • Automotive
    • Heating ventilation and air conditioning (HVAC)
    • Lighting
    • Central gateway/in-vehicle networking
    • Gasoline engine management
  • Industrial
    • Programmable logic control (PLC)
    • Process control, temperature control
    • Input-output control (I/O Control)
    • Single board comp

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