ams Creates Fuel Gauge Reference Design for Electric Scooters

ams reference design for battery fuel-gauging in electric scooters

ams has developed a reference design that shows how a simple current and voltage measurement circuit can produce state of charge (SOC) readings for electric scooter batteries. The reference design features ams’ AS8510, which is a two-channel battery sensor interface. The reference design is available free to ams customers.

In addition to an ams AS8510 sensor interface, the reference design features a simple 8-bit microcontroller, a LDO and a LED driver (driving an LED bar-graph display). The design replaces a voltmeter display with an accurate fuel gauge. This makes it easier for riders of battery-powered scooters to see exactly how much power remains, and figure how far they can ride before needing to recharge. The bill-of-materials cost for the active components is about $3.70 (€ 3).

Electric scooters are typically powered by four series-connected 12V lead-acid batteries. The ams circuit design captures simultaneous current and voltage measurements for each of the four batteries at a high sampling rate. Demonstration software implemented in an 8-bit microcontroller converts a combination of open-circuit voltage measurements and coulomb counts into SOC readings.

The ams reference design supports a simple LED bar graph display, but it can also be used to drive a more expensive LCD display to provide more precise information to the rider. The software developed by ams is provided at no cost to demonstrate that fuel-gauging can be successfully implemented in the reference hardware design, and to show how accurate and precise voltage and current measurements can be used to produce valid SOC readings.

At the heart of the e-scooter fuel-gauging reference design is the ams AS8510 sensor interface. The AS8510 integrates data acquisition and data conversion in a single chip. The device produces virtually offset-free current and voltage measurements across a wide, dynamic range.

AS8510 Data Acquisition Front-End IC Features

  • 3.3V supply voltage
  • Two independent, fully differential, high resolution 16 bit A/D converters with programmable over sampling ratio to enable sampling rates from typically 1kHz to below 1 Hz
  • Precision, low noise, programmable gain amplifiers for both channels for gains 5, 25, 40, 100
  • Offset auto zero architecture on both channels
  • Two additional multiplexed single ended inputs including programmable 250 uA current source for external temperature sensor
  • Internal temperature sensor
  • High precision and high stability 1.2V reference voltage source
  • Digital filter options for both channels
  • Various operating modes for normal and standby operation
  • Standby current monitoring for active wake with 40 uA average current consumption, programmable threshold
  • Micro controller interface through 4 wire SPI
  • On chip 4MHz RC oscillator or external clock
  • -40° C to +125° C ambient operation
  • AEC Q 100 automotive qualified
  • Internal chip ID for full traceability
  • SSOP20 package

More info: ams AG