General Description

AS6040 is an ultrasonic flow converter (UFC) solution dedicated to gas meters, but suitable for water meters, too. The system is made of four major blocks: supervisor, frontend, post processing and interface. The supervisor manages all tasks and is the master of the whole system, making the AS6040 autonomous. The front-end integrates a high-voltage driver, an integrated programable gain amplifier (PGA) and an offset-stabilized comparator in the receive path, a precision TDC for the time-of-flight measurement, amplitude measurement as well as an RDC unit for temperature measurement. In flow meter mode, the 32-bit CPU in combination with 4k of ROM code and 4k of NVRAM does the post processing for flow calculation. In time conversion mode the CPU is not active and the chip sends the raw time-of-flight data. It communicates to an external microcontroller via SPI interface. By means of the integrated pulse interface the AS6040 can run also in stand-alone mode.

The analog front-end is supported by an integrated charge pump to provide a programmable fire voltage in the range from 5.6 V o 18 V with a frequency from 40 kHz up to 1 MHz. The integrated PGA gain factor can be adjusted from 2 to 132 V/V. The first hit level detection starts with a programmable offset up to 200mV. After this is set down to 0 mV, the AS6040 can measure up to 31 zero crossings within a single receive burst. The front end achieves in single shot less than 300 ps rms noise single shot with good 500kHz transducers. The first-hit pulse width information and the amplitude can be used to regulate the first hit level and maintain a stable operation over whole range for ultrasonic flow meters. It comes in a compact QFN48 package and allows compact designs thanks to a small number of external components.

Benefits Features

Single-chip solution provides ready flow information

System design compatible with mechanical meters

High flexibility in choice for external μP handling communication and further data management

High performance + ultra-low power 32-Bit CPU

120 * 32 bit NVRAM (non-volatile RAM) for user firmware parameter & data

3968 * 8 bit NVRAM (non-volatile RAM) for user firmware program code

4k * 8 bit ROM for system task code and special flow library code

Operation from Battery

Precision down to low flow rates

Leakage detection

Handles weak signals for small transducers and multiple reflections

On-chip charge pump to generate drive voltage for ultrasonic transducer

40 kHz to 1 MHz at 5.6 V to 17.8 V drive voltage, generated from battery supply

Integrated PGA, gain 2 to 132 V/V

First hit level and phase detection

Amplitude measurement

Up to 31 zero crossing measurements

Precision time-to-digital converter and low-noise front-end with < 300 ps single shot with good 500kHz transducers on a residential gas meter

Ultra-low power consumption

Compact design

Low BOM

SPI serial interface

General Purpose I/O Unit incl. pulse interface and 2-wire master interface (I2C like)

Supply voltage 2.8V to 3.6 V

3.0 to 3.6 V NVRAM store only

Operating temperature -40 to 85°C

QFN48 package (7 x 7mm²)

Applications

● Residential gas meters

● Industrial gas meters

● Clamp-on water meters

● Volume counters