The 33975 Multiple Switch Detection Interface with Suppressed Wake up is designed to detect the closing and opening of up to 22 switch contacts. The switch status, either open or closed, is transferred to the microprocessor unit (MCU) through a serial peripheral interface (SPI). The device also features a 22-to-1 analog multiplexer for reading inputs as analog.
The 33975 device has two modes of operation, Normal and Sleep. Normal mode allows programming of the device and supplies switch contacts with pull-up or pull-down current as it monitors the switch change of state. The Sleep mode provides low quiescent current, which makes the 33975 ideal for automotive and industrial products requiring low sleep state currents.
Improvements are a programmable interrupt timer for Sleep mode that can be disabled, switch detection currents of 32 mA and 4.0 mA for switch-to-ground inputs, and an interrupt bit that can be reset. This device is powered using SMARTMOS technology.

Features
• Designed to operate from 5.5 V ≤ VPWR ≤ 28 V
• Switch input voltage: (33975: -14 to 38 V) (33975A: -14 to 40 V)
• Interfaces to microprocessor using 3.3 V/5.0 V SPI protocol
• Selectable wake-up on change of state
• 14 switch-to-ground inputs
• 8 programmable inputs (switches to battery or ground)
• Selectable wetting current (32 mA or 4.0 mA for switch-to-ground inputs)
• Sleep State current VPWR 100 μA, VDD 20 μA

Applications
• Automotive systems
• Industrial control systems
• Process control systems
• Security systems
• Systems requiring switch status verification for safety, operation, or process control purposes