TPIC8101 Training

7/31/2019 TPIC8101 Training

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Knock Sensor TrainingTPIC8101

6/27/2011 1

Thomas Cosby


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Knock Sensor Basics

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Knock Sensor - Background

Almost all cars have knock sensors to meet OBDII emissions control requirements.

Engine knock can occur when the charge inside the cylinder detonates causing apinging sound. This can be a result of:

Improper engine timing Using the wrong octane gasoline Worn or defective spark plugs

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Cars/Trucks have knock sensors mounted on the engine block

Knock sensors are piezo-electric elements The vibrations of the engine are converted into electric signals

Knocking is controlled using spark timing


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Knock Sensor - Types

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Knock sensor construction

Piezo element to detect pressure wave.

Resistor element to for open load

detection

Signal returns and cable shield.


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Knock Sensor Mounting Location

ENGINE

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Most engines

have two knock

sensors

SENSOR


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Ignition System Timing

Intake C cle Com ression C cle

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Combustion Cycle Exhaust Cycle


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Knock Sensor - Waveforms

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Typical noise content in a running engine. Typical flat response type knock signal

Typical places where noise occurs in the ignition cycle. Typical resonant response type signal.


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TPIC8101: Knock Sensor Interface

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TPIC8101: Knock Sensor Interface

Engine Knock Detector Signal Processing

Analog Signal Processing With Filter Characteristics

- Piezoelectric sensing

- Accelerometer sensing

Dual-channel Engine Knock Sensor Interface

External Clock Frequencies up to 24 MHz 4, 5, 6, 8, 10, 12, 16, 20, and 24 MHz

SPI interface (for Microprocessor)

Programmable Gain

Pro rammable Band-Pass Filter enter Fre .

Package: DW (20-pin, 1.27 mm pitch)

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Broad C selection via 9 selectable ext. clock

frequencies

Selectable input channels improve accuracy

Choice of output signal profile: analog or digital

Can use for general analog signal processing

Advanced SPI mode capability available

System-level diagnostics of device capable via

Test Mode

Programmable Input Frequency Pre-scaler

Operating Temp. Range: - 40C to 125C


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Knock Sensor Applications Schematic

+

-

+

-

+

-

VDD/2Vref

Mux

3rd Order AAF

SAR

10-bit ADC

fs = 200 kHz

Programmable

Gain

Programmable

Band-Pass Rectifier

Programmable

CH1P

CH1N

CH1FB

CH2P

CH2N

CH2FB

100 nF

Knock Sensor 1

3.3 nF

R

R R

R

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Microcontroller

A/D

Filter

+

-

R2R

10-bit DAC

fs = 200 kHz

SPI

Test Mode

DSP Control

DSP

VDD GND OUT

XIN

XOUT 1 M

1 k

470 pF

CS__

SCLK SDI SDO TEST____

INT / HOLD

Knock Sensor 2

3.3 nF

Note: R > 25 k


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Engine Knock Sensor Key Parameters

Basic DC Quiescent Condition Parameters Quiescent current (IDDQ): 7.5 mA (typ.)

Max. Operating current (IDD(OP)): 20 mA

Hysteresis Voltage (Serial IF & Pre-scaler): 0.4 V (typ.)

Input Amplifier Parameters Cross-coupling attention: 40 dB (min.)

Open-loop gain (Av): 100 dB (typ.)

Gain Bandwidth Product: 2.6 MHz (typ.)

Output (Buffer) Amplifier Parameters High-level output volt. (VOH): VDD-0.15 (typ.)

Low-level output volt. (VOL): 175 mV (max.)

Ripple voltage: 10 mV (max.) Settling time (ts): 20 s (max.)

Anti-Aliasing Filter Parameters Frequency response (1 kHz to 20 kHz): 1 dB

Attenuation @ 100 kHz: -15 dB to -10 dB

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se o age npu : - m o m

CMRR range: 60 80 dB

Prescaler/Oscillator Parameters: Min. input peak amplitude: 150 mV

Input Capacitance: 7 pF

Leakage Current: -1 A to +1 A

Operating Temperature Range: -40C to +125C

- requency ange: z o z

Recommended Operation Conditions Regulated input voltage (VDD): -0.3 V to +5.5 V

Output voltage range (buffer): -0.3 V to +5.5 V

Input voltage range: 0.05 V to (VDD-0.05) V

DC Input Current (IIN): 1 A> for CH1P, CH1N, CH2P, and CH2N pins

DC Input Voltage (VDCIN): VDD> for CH1P, CH1N, CH2P, and CH2N pins Continuous Power Dissipation: 100 mW (max.)


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TPIC8101 Knock Sensor Block Diagram

AINVIN

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Auto

AO

tINTVO

ABPAP AINTC

(System Transfer Function)


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TPIC8101 Transfer Function

IN

RESETOUT

C

INTBPPININTBP

BP

INOUT

RESETOUT

C

INTBPPIN

TINT

BP

BP

INOUT

RESETOUT

C

INTBPPIN

T

BPINOUT

V

VAt

AAAATff

VV

VA

t

AAAAtf

f

VV

VAt

AAAAdttfVVINT

+=

+=

+=

1

*1

*****))cos(1(*

*1

*****)cos((*

*1

*****)sin(

0

0

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RESETOUT

C

INTINTBPPIN

INOUT

RESETOUT

C

INTINTBPPIN

INOUT

INT

RESETOUT

C

INTBPPININTBP

BP

OUT

VAt

TAAAA

VV

VA

t

TAAAA

VV

f

NT

tf

+=

+=

=

+=

******2*

******))1(1(*

cos


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TPIC8101 Transfer Function, continued

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TPIC8101 Input Settings

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AIN = R2/R1

VIN2 channels


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TPIC8101 DSP Settings

ABPAP AINT = 2C

ABP = 2 at the center frequency.

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Datasheetpage 10

AP APC

Set to match sensor outputs

Assumes that AIN = 1.


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TPIC8101 Integrator Programming

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TPIC8101 Integrator Programming, continued

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TPIC8101 SPI Interface

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TPIC8101 Default SPI Mode

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TPIC8101 Advanced SPI Mode

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TPIC8101 Test Mode

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TPIC8101: Application Example

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Application Requirements

Requirements: VIN = 7.3KHz, 300mVpp (Knock Sensor specification)

Oscillator = 6MHz (Microprocessor clock specification)

Knock window (TINT)= 3ms (system spec)

OUT = 4.5V (Microprocessor interface specification)

Need to set:

Input amplifier gain (AIN)

Programmable gain (AP)

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Integration time constant (TC)

Set AIN = 1; R1 = R2

TC is typically TINT/(2**VOUT)

TC = 3ms / (2**4.5) = 106s

4.5V = 0.15*AP*2.55*3ms/100s + 0.125

AP = 0.38


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TPIC8101 Application Schematic

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TPIC8101 SPI Settings

Parameter Calculated Programmed Code SPI

Value Value DEC HEX

Oscillator 6MHz 6MHz 01000010

Channel 1 1 11100000

fC0 7.3KHz 7.27KHz 42 2A 00101010

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AP 0.38 0.381 34 22 10100010

TC 106s 100s 10 0A 10001010

TINT 3ms


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TPIC8101EVM Waveforms

7270KHz,

300mVpp

INT,

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Output

4.48V

TPIC8101 Training

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