AS1716

Capacitive Sensor Interface

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1 General Description

AS1716 is an analog front end specifically designed for

unbiased Capacitive Sensors, as for instance Knock

Sensors in Automotive, to be interfaced with Analog Dig-

ital Converters with Sample and Hold input stages.

The device provides differential inputs, a 1st order low

pass filter to cutoff the high frequency noise compo-

nents, differential to single ended conversion, program-

mable gain stage and a 2 pole low pass Multiple

Feedback Filter.

The Knock Sensor is a Piezo Electric device that gener-

ates a voltage if it is stressed. It senses knock and trans-

mits information to the electronic engine management

control unit. This influences process control in the

engine, for example timing and fuel injection until knock

is eliminated.

The capacitive sensor is biased via resistors to a voltage

Figure 1. AS1716 Block Diagram

2 Key Features

!

Differential input stage with wide input range

!

!

Programmable Gain (x0.5, x1, x2, x4)

!

Internal 2

with a min. cut off frequency of 16kHz

!

Single supply operation: 4.5V to 5.5V

!

Operating Temperature range: -40°C to +125°C

!

High CMRR: 55dB (min)

!

EMC characterized by IEC 61967-4

(1

Ω / 150Ω Method)

!

EMC characterized by IEC 62132-4

(Direct Power Injection)

!

Automotive qualified to AECQ100 for IC and PPAP

level 3

!

8-pin SOIC Package

3 Applications

Analog front end for Capacitive Sensors to Analog to

Digital Converters and DSP.

+

-

-

+

-

+

VDDA

VDDA/2

Multiple Feedback LP Filter

fc ~23kHz typ.

INP

GA

GB

OUT

NC

VSSA

VDDA

Gain Control

x0.5, x1, x2, x4

-

+

VDDA/2

VDDA/2

VDDA/2

-

+

VDDA/2

INN

AS1716