EVALUATION KIT AVAILABLE MAX35104 Gas Flow Meter SoC General Description Benefits and Features The MAX35104 is a gas flow meter system-on-chip (SoC) High Accuracy Flow Measurement for Billing and targeted as an analog front-end solution for the ultrasonic Leak Detection gas meter and medical ventilator markets. With a time Time-to-Digital Accuracy Down to 700ps measurement accuracy of 700ps and automatic differen- Measurement Range Up to 8ms tial time of flight (TOF), the device makes for simplified 2 Channels: Single-Stop Channel computation of gaseous flow. High Accuracy Temperature Measurement for Precise Power consumption is the lowest available with ultra-low Flow Calculations 62A time-of-flight measurement and 125nA duty-cycled One 2-Wire Sensor: PT1000, PT500 RTD, and Thermistor Support temperature measurement. Multi-hit (up to six per wave) capability with stop-enable windowing allows the device to Maximizes Battery Life with Low Device and Overall be fine-tuned for the application. Internal analog switches, System Power a configurable three-stage integrated operational ampli- Ultra-Low 62A TOF Measurement and 125nA fier chain amplifier, and an ultra-low input offset compara- Duty-Cycled Temperature Measurement tor provide the analog interface and control for a minimal Event Timing Mode with Randomizer Reduces electrical bill of material solution. A programmable high- Host C Overhead to Minimize System Power voltage (up to 30V) pulse launcher provides up to 19dB of Consumption transducer launch amplitude adjustment to compensate 2.3V to 3.6V Single-Supply Operation for transducer aging and temperature, pressure, humidity High Integration Solution Minimizes Parts Count and affects. Early edge detection ensures measurements are Reduces BOM Cost made with consistent wave patterns to greatly improve Built-In Real-Time Clock accuracy and eliminate erroneous measurements. Built-in Small, 5mm x 5mm, 40-Pin TQFN Package arithmetic logic unit provides TOF difference measure- -40C to +85C Operation ments and programmable receiver hit accumulators to minimize the host microprocessor access. For tempera- ture measurement, the device supports a single 2-wire PT1000 platinum resistive temperature detector (RTD) or NTC thermistor. A simple 4-wire SPI interface allows any microcontroller to effectively configure the device for its Ordering Information appears at end of data sheet. intended measurement. Applications Ultrasonic Gas Meters Medical Ventilators 19-8501 Rev 3 12/17MAX35104 Gas Flow Meter SoC TABLE OF CONTENTS General Description ............................................................................ 1 Benefits and Features .......................................................................... 1 Absolute Maximum Ratings ...................................................................... 6 Package Thermal Characteristics ................................................................. 6 Recommended Operating Conditions .............................................................. 6 Electrical Characteristics ........................................................................ 6 Recommended External Crystal Characteristics......................................................11 Timing Diagrams ..............................................................................11 Pin Configuration ............................................................................. 13 Pin Description ............................................................................... 13 Block Diagram ............................................................................... 16 Detailed Description........................................................................... 16 Time-of-Flight (TOF) Measurement Operations 17 Pulse Echo TOF Mode . 19 Early Edge Detect 19 TOF Error Handling . 20 Step-Up DC-DC Controller 20 Control and Operation . 20 Compensation Component Values . 21 RSENSE 21 Kelvin Sense 21 Power Transistor . 21 Inductor (L) 23 Diode 23 Output Filter Capacitor . 23 Piezo Driver Regulator . 23 Output Capacitor Selection . 23 Transducer Driver . 23 Analog Front-End . 24 Temperature Measurement Operations 26 Temperature Error Handling 26 Event Timing Operation 27 Continuous Event Timing Operation 27 Continuous Interrupt Timing Operation 27 TOF Sample Randomizer 27 Event Timing Mode 2 28 Event Timing Mode 3 30 Event Timing Mode 1 30 Maxim Integrated 2 www.maximintegrated.com