MAX1441 Datasheet, PDF(8/41 Page) Maxim Integrated Products – Automotive, Two-Channel Proximity and Touch Sensor

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MAX1441 Datasheet, PDF (8/41 Pages) Maxim Integrated Products – Automotive, Two-Channel Proximity and Touch Sensor

◁

Automotive, Two-Channel Proximity and

Touch Sensor

TCK

TDI, TMS

TDO

Figure 1. JTAG Timing Diagram

Detailed Description

The MAX1441 is a 2-channel proximity and touch sensor

that contains all the functions necessary to implement

a proximity/touch detection system for vehicle PRKE

systems and other applications. There are four principal

architectural components to the device: the capacitive

sensing analog front-end (AFE), a programmable CPU

system, vehicle power, and I/O interface. Figure 1 shows

the JTAG timing diagram.

The AFE uses a 2-channel C2D converter to measure the

capacitance present between sensor inputs SINPUT1

and SINPUT2 and the ambient ground (Figure 2). The

AFE-sensing architecture converts approaching hand

motion to 12-bit digital words that are operated by

an algorithm in the CPU to ensure detection of posi-

tive events and minimizing false detections. The C2D

converters can measure the input capacitance in three

different ranges: 20pF, 10pF, and 5pF. Additionally, the

C2Ds compensate up to 63pF of parasitic capacitance

programmable in 1pF steps.

In addition to capacitive proximity and touch detection,

the AFE contains POR and a watchdog timer for monitor-

ing CPU operations. The CPU runs the input capacitive

data through an algorithm to ensure detection of positive

events and minimizing false detections. The CPU system

includes Flash-based program memory, SRAM, clocks,

and communications. The power input and signal out-

puts provide a complete interface to the vehicle power

system and a robust communication signal to remote

electronic control modules (ECUs).

Technical Function

Each C2D converter produces an AC excitation voltage

at inputs SINPUT1 and SINPUT2. The excitation voltage

forces current through the capacitance connected to the

sensor input. The current amplitude is proportional to the

measured capacitance. The circuit measures the input

capacitance by measuring the current flowing through

the sensor inputs. This excitation signal is a sine wave

with a frequency programmable from 100kHz to 500kHz

in10kHz steps. The sinusoidal excitation allows for much

lower EMI emissions compared to architectures that uti-

lize simple square-wave excitation.

The device drives the guard outputs AGUD1 and AUGD2

with the same signal from the sinusoidal excitation and

shields the sense electrodes without adding parasitic

capacitance. The converter measures the amplitude of

the current and converts it to 12-bit digital data by a

12-bit C2D. The maximum conversion rate in each of the

sensor channels is 1.66kHz.

The microcontroller reads the input capacitance values

and uses a user-supplied custom algorithm to detect

the object proximity. Once the proximity is detected,

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