SCDS434 October 2021 TMUX8212
Refer to the PDF data sheet for device specific package drawings
Multiplexing PMU systems enables a small, flexible solution that can be used over a wide range of current ranges. TI’s high voltage multiplexers offer a size advantage over typical relay solutions while still achieving an extremely low level of distortion, noise, and leakage. This high voltage multiplexer can be use in tandem with high voltage operational amplifiers and DACs to create an accurate PMU with excellent signal-to-noise ratio.
In this example application, the TMUX8212 is paired with a high voltage amplifier and a DAC. The DAC generates an arbitrary voltage signal that feeds into the amplifier. An additional high voltage offset is also fed into the amplifier to add any needed common mode shift. This arbitrary signal is then passed through a current limiting resistor before reaching the DUT. To change the current range of the system, different current limiting resistors are added in series with each channel of the multiplexer. In this example, the first channel of the multiplexer uses a 10k Ω resistor for the low current clamp. This ensures the maximum output current of the PMU in this range will be 5 mA. During the system operation, the PMU will be set to this lower current range in the beginning of the test routine. After the DUT is initially checked in this range and is found to be operating normally with no unexpected shorts, the current range can be switched to high current. This insures that the PMU and DUT will not be unnecessarily damaged from excess current due to a short. In this example, the remaining three channels of the TMUX8212 are connected in parallel, increasing the maximum current through the device and reducing the low on-resistance. Because of the flexibility of the TMUX8212, this could easily be modified to fit any system need. For example, if less max current is need, two channels could be connected in parallel instead of three and the additional single channel could be used to add a third current range option. This multiplexed application becomes increasingly valuable with larger number of input channels by greatly reducing solution size.
The TMUX821x switches have exceptionally flat on-resistance and low leakage currents across the signal voltage range. The ultra-flat on-resistance ensures that the current clamp stays constant across the signal voltage range. And the low leakage current reduces the potential noise/offset when measuring on the lowest current range. Additionally, excellent crosstalk and off-isolation performance allows the TMUX821x devices to preform well in multi-channel switching applications without having an unselected channel impact the measurement on selected channels.