Description:

We were designing a PCB test fixture for our fire extinguisher controller PCB. This PCB contains a supercapacitor and a lithium backup battery. And becuase we want to guarantee 10-15 years of maintenance free operation, it's imperative that we perform a 100% production test of leakage currents on those circuits. That is easily done using equipment like precision power supplies or sourcemeters. But that is a costly endeavour. Besides that, we like to have our testers as complete as possible with little or no setup time.

The coincell simulator was designed to simulate a coincell or super capacitor with an accurate set voltage and a two-quadrant current flow and precision measurement capabilities. In order to make it easy to interface with, the simulator uses an I²C port to access the DAC and ADC directly. The simulator output starts in 3-state mode.

Using our USB-I²C Interface Adapter and some Python code, the coincell simulator is easily configured and monitored.

Specifications:

• Output voltage 0-5.0V
• Current limited by op-amp and sense resistor
• 12-bit DAC (MCP47CVB22) followed by op-amp ≥200mA (MCP651)
• Reference 2.5V 0.1% (MCP1502)
• 20-bit voltage and current monitor (INA228)
• 2kbit EEPROM for calibration constants
• Power-on with 3-stated output (2^nd DAC channel controls #CS signal)
• Output sense resistor as through hole component for easy adjustment
• Isolated 5V/1W power supply and I²C interface
• 0.1" screw terminals for output
• Up to two devices on one I2C bus
• Requires 5V I²C bus voltage
• JST SH connector 4-pin ×2
• Dimensions 40×26mm