MAX1441双通道接近检测和触摸传感器应用电路

  The MAX1441 proximity and touch sensor  is designed for capacitive proximity sensing in automotive Passive Remote Keyless Entry (PRKE) and other applications. This device provides signal processing to support two independent touch/proximity sensor channels. The device features two open-drain output pins with high-voltage capability up to 28V as well as five digital I/Os to indicate sensing events. During manufacturing JTAG programming uses four digital I/Os.
  
  The device uses grounded electrode capacitive sensing to measure capacitance between one of the two sense pins and the ground. A hand approaching a sense electrode attached to these sense pins causes a change in measured capacitance indicating the presence (touch or proximity) of the object. Active guard outputs shield the sense electrode from unwanted sources without adding parasitic capacitance. Spread-spectrum techniques in the sensor excitation circuit reduce both electromagnetic emissions and susceptibility to interfering signals. In addition, the sensing excitation frequency is programmable from 100kHz to 500kHz in 10kHz steps to avoid interference.
  
  The sensor input signals are converted to a 12-bit digital data and are available to an on-chip microcontroller (µC). The device provides independent offset-compensation of up to 63pF for each input channel. Each channel can be programmed to 5pF, 10pF, or 20pF full-scale range.
  
  The device features an internal MAXQ® microcontroller with 2kword of flash for user programs and 128 bytes of SRAM. This feature provides the ability to implement customized signal processing and discrimination algorithms that optimize performance in the systems. The device offers user-configurable general-purpose digital I/O lines. Power-on-reset circuitry provides consistent startup of the device, and a watchdog timer ensures long-term reliable operation of the user's software.
  
  The device is available in a 20-pin TSSOP package and is specified over the -°C to +105°C automotive temperature range.