Maxim-integrated MAXQ7667 Bedienungsanleitung PDF herunterladen (Seite 299)

17.4 Burst Signal Generation

To facilitate implementation the following items must be addressed:

•

Hardware Setup:

External RC Filter (FILT)

Ultrasonic Transducer

•

Software Setup:

Turning On the PLL and the Clock Sections

Configuring the Burst Registers

Triggering the Burst Signal

17.4.1 Setting Up the Hardware

17.4.1.1 External RC Filter (FILT)

An external filter must be connected to the FILT pin if the PLL is used. This filter consists of two capacitors and one resistor (R1 = 24kΩ,

C1 = 0.033µF, and C2 = 330pF) as shown in Figure 17-1. These values are appropriate for the entire PLL frequency range. These com-

ponents are used to filter the analog voltage that controls the voltage-controlled oscillator, VCO, in the PLL. The FILT pin can be mon-

itored with an oscilloscope to gauge the settling time of a change in the PLL frequency setting.

17.4.1.2 Ultrasonic Transducer

There are many ways to connect the ultrasonic transducer to the BURST pin. Figure 17-3 shows one of the possibilities.

17.4.2 Setting Up the Registers in Software

17.4.2.1 Turning On the PLL and the Clock Sections

To reduce power consumption, many sections of the MAXQ7667 are not powered up unless needed. To turn on the PLL, set the PLLE

bit (APE.3) to 1. The MAXQ7667 operates from the internal RC oscillator at power-up and only switches to the crystal-controlled clock

if instructed to by the software. To turn on the precision system clock that is controlled by the external crystal or resonator, set the XTE

bit (OSCC.1) to 1 (see

Section 15).

17-17 _________________________________________________________________________________________________________

MAXQ7667 User’s Guide

MAXQ7667

0.01µF

470pF

BURST

12V

TRANSDUCER

ECHON

0.01µF

470pF

ECHOP

Figure 17-3. Circuit for Ultrasonic Distance Measurement

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Maxim-integrated MAXQ7667 Bedienungsanleitung Seite 299