Time-to-Digital Converter with Analog Front-End

Accurate Low Flow Measurement with Low System Power Consumption

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The MAX35101 is a time-to-digital converter with built-in amplifier and comparator targeted as a complete analog front-end (AFE) solution for the ultrasonic heat meter and flow meter markets.

With a time measurement accuracy of 20ps and automatic differential time-of-flight (TOF) measurement, this device makes for simplified computation of liquid flow. Early edge detection ensures measurements are made with consistent wave patterns to greatly improve accuracy and eliminate erroneous measurements.

Multihit capability with stop-enable windowing allows the device to be fine-tuned for the application. Internal analog switches, an autozero amplifier/comparator, real-time clock (RTC), and programmable receiver sensitivity provide the analog interface and control for a minimal electrical bill of material solution. The RTC provides an event timing mode that is configurable and runs cyclic algorithms to minimize microprocessor interactivity and increase battery life.

Built-in arithmetic logic unit provides TOF difference measurements. A programmable receiver hit accumulator can be utilized to minimize the host microprocessor access and thus minimize current consumption.

For temperature measurement, the MAX35101 supports up to four (4) 2-wire PT1000/500 platinum resistive temperature detectors (RTD).

A simple 4-wire SPI interface allows any microcontroller to effectively configure the device for its intended measurement.

On-board 8KB user flash allows the MAX35101 to be nonvolatile-configurable and provide nonvolatile energy use data to be logged. Configuration can be recalled anytime with a SPI command. 
MAX35101: Typical Application Circuit MAX35101: Typical Application Circuit Enlarge+

Key Features

  • High Accuracy Flow Measurement for Billing and Leak Detection
    • Time-to-Digital Accuracy Down to 20ps
    • Measurement Range Up to 8ms
    • Two Channels: Single-Stop Channel
  • High Accuracy Temperature Measurement for Precise Heat and Flow Calculations
    • Up to Four (4) 2-Wire Sensors
    • PT1000 and PT500 RTD Support
  • Maximizes Battery Life with Low Device and Overall System Power
    • Low 10µA ToF measurement and < 125nA Duty-Cycled Temperature Measurement
    • Event Timing Mode Reduces Host µC
  • Overhead to Minimize System Power Consumption
    • 2.3V to 3.6V Single-Supply Operation
  • High-Integration Solution Minimizes Parts Countand Reduces BOM Cost
    • 8KB of Nonvolatile Flash Memory for Data Logging
    • Built-in Real Time Clock
    • Small, 5mm x 5mm, 32-Pin TQFP Package
    • -40°C to +85°C Operation


  • Ultrasonic Gas Meters
  • Ultrasonic Heat Meters
  • Ultrasonic Water Meters
Part Number Sensing Element PGA Gain Calibration Method Output Type ICC
Interface VSUPPLY
Package/Pins Budgetary
typ See Notes
MAX35101  Ultrasonic Piezoelectric Transducer Fixed External microcontroller Digital 0.01 SPI 2.3 to 3.6
$3.94 @1k
See All Sensor Signal Conditioners (12)
Pricing Notes:
This pricing is BUDGETARY, for comparing similar parts. Prices are in U.S. dollars and subject to change. Quantity pricing may vary substantially and international prices may differ due to local duties, taxes, fees, and exchange rates. For volume-specific and version-specific prices and delivery, please see the price and availability page or contact an authorized distributor.

Device   Fab Process   Technology   Sample size   Rejects   FIT at 25°C   FIT at 55°C  

Note : The failure rates are summarized by technology and mapped to the associated material part numbers. The failure rates are highly dependent on the number of units tested.

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