- Current ranges output:
- 0-3300 nA/µA/mA (Unidirectional mode)
- +/- 0-1650 nA/µA/mA (Bidirectional mode)
- Burden voltage:
- Output offset voltage¹: typically <10µV, max 50µV
- Maximum input voltage differential (see Safety): 33mV
- +/-0.05% (µA, nA ranges)
- +/-0.1% (mA range)
- Highest resolution (nA range):
- 100pA (3.5digit meter)
- 10pA (4.5 digit meter)
- 1pA (5.5 digit meter)
- Cascaded MAX4239 amplifiers with 100x output gain
- Bandwidth: >300KHz (-3dB)
Note¹: it may take a few minutes from power ON for the offset to reach its lowest value (ie. warm-up).
Architecture and principle of operation
At the heart of the CurrentRanger are two MAX4239 ultra low offset auto-zero 6Mhz unity gain bandwidth amplifiers. They are configured in a non-inverting 10x gain each using high precision resistors, totaling 100x output gain.
There are 3 high precision shunts (10mΩ, 10Ω, 10kΩ) at the input of these amplifiers yield the 3 current sensing ranges possible.
While the amplifiers, topology and shunt configuration of the CurrentRanger are similar to the µCurrent by EEVBlog, CurrentRanger is a product with significantly different features and goals.
The CurrentRanger employs switching dynamics to selectively enable/disable the shunts to allow for manual or auto-ranging.
The analog sensing is done by the SAMD21G18 ARM Cortex M0+ 48Mhz processor which samples the output through its 12bit ADC. The SAMD21 also controls all aspects of switching, digital interfacing, and power control of the unit.
A lot of development and experimentation were invested to bring this product to reality. And it could still be improved, made lower noise, enhanced with more features, etc. This is where you – the user – have an opportunity to contribute with suggestions, analog and EE expertise and coding optimizations. Thank you to all who’ve provided great feedback and contributed in some way!