Maxim公司的MAX1441是接近式和触摸传感器IC,14V的工作电流只有100uA, 1.2fF LSB电容/数字分辨率,工作电压5V-28V,45V过压保护,2k字闪存,128B SRAM,传感器I/O线±2kV ESD保护,JTAG接口,支持两个单独接地电容传感器输入.主要用在无源遥控钥匙(PRKE)系统接近传感和物件检测系统.本文介绍了MAX1441主要特性,方框图, 典型应用电路图以及MAX1441评估板主要特性,电路图,材料清单和PCB布局图.

The MAX1441 proximity and touch sensor IC 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 (FC). 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 (POR) 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 -40NC to +105NC automotive tem­perature range.

MAX1441主要特性:

Low Average Operating Current (100μA at 14V)

1.2fF LSB Capacitance-to-Digital Resolution (5pF Range)

5V to 28V Operation

45V Overvoltage Protection

Sinusoidal Excitation for Reduced EMI Emissions

Frequency Spreading Operation for Reduced EMI Susceptibility and Emissions

Active-Guard-Sense Architecture Provides Increased Flexibility in System Packaging

CMOS/LVCMOS-Compatible Outputs

Embedded μC Supports User-Specified Adaptive Sense Algorithms

2kwords Flash Memory

128-Byte SRAM

±2kV ESD Immunity on Sensor I/O Lines

JTAG Serial Interface

Supports Two Independent Grounded Capacitor Sensor Inputs

-12V Reverse Voltage Protection with External Diode

MAX1441应用:

PRKE System Proximity Sensing

Object Detection Systems

图1. MAX1441方框图

图2. MAX1441典型应用电路图

MAX1441评估板
 
The MAX1441 evaluation system (EV system) provides a proven design to evaluate the MAX1441 capaci­tive proximity and touch sensor. The EV system con­sists of two PCBs. The MAX1441 evaluation kit (EV kit) includes the typical application circuit and all electronics for USB-to-JTAG communication between the on-board device and the PC. The MAX1441TP evaluation kit (TP EV kit) includes two touch pads. The TP EV kit connects to the EV kit through 20-pin right-angle connectors. The EV kit board connects to either the factory-provided kit touch pads board, or a custom user-supplied touch sensor. The EV sys­tem also includes Windows XPM- or Windows VistaM-compatible integrated development environment (MAX-IDE) for the MAXQM microcontroller core of the device.

The EV kit comes with a MAX1441GUP/V+ installed.

MAX1441评估板主要特性:

Wide 6V to 28V VBAT Supply Range

External Touch-Sense Pad Included

Adaptive Firmware Source Code Included

USB PC-to-JTAG Connection

USB Powered or Battery Powered

Compatible with the MAX-IDE Development Tool

Proven PCB Layout

Fully Assembled and Tested

图3.MAX1441评估板电路图(1)

图4.MAX1441评估板电路图(2)

图5.MAX1441评估板电路图(3)

图6.MAX1441评估板电路图(4)

图7.MAX1441评估板电路图(5)

图8.MAX1441评估板电路图(6)
MAX1441评估板材料厂清单:



图9.MAX1441评估板PCB布局图
详情请见:
http://datasheets.maxim-ic.com/en/ds/MAX1441.pdf
和
http://datasheets.maxim-ic.com/en/ds/MAX1441EVSYS.pdf