Similar to the isolated gate drivers, isolated voltage sensors require power supply both on the HV and the LV side to transfer a signal from the DC link (HV side) to the MCU (LV side) across the isolation barrier. This can be achieved using a transformer plus driver combination, such as the UCC28700-Q1 device, to provide both sides with a supply voltage, but TI also offers isolated voltage sensors with an integrated power supply.

Here, the AMC33xx-Q1 family of devices (for example, the AMC3330-Q1 device) significantly reduces the complexity of the system using an internal isolated DC-DC converter, which allows single-supply isolation from the low-side of the device. At the input, ±1V can be applied for voltage measurements with high input impedance, such as resistor-divider networks to sense high-voltage signals. This device features an analog output.

To sense voltage in HV systems, a resistor ladder must be placed at the input of the voltage sense device to reduce the voltage at the input to a scale that is acceptable for the voltage sense IC. This resistor-divider network adds space and potentially costs to the system and must be finely trimmed to achieve the wanted output voltages. TI offers a matched resistor divider with 12.5MΩ of fixed input resistance and up to 1400VDC of input voltage—the RES60A-Q1 device, features high ratio matching precision within ±0.1% of the nominal.

The AMC038x-Q1 family of devices (for example, the AMC038D-Q1 device) handles this problem by providing an integrated resistive divider, see Figure 10-2. The resistive divider at the input scales down the voltage applied to the HVIN pin to a ±1V linear full-scale level. This signal is also available on the SNSP pin. The output of the device is a differential signal proportional to the input signal.

Figure 10-2 AMC0380D-Q1 Block Diagram

The integrated resistive divider enables significant board space savings, see Figure 10-3. Simultaneously, accuracy is improved due to the gain error being calibrated still at factory and very low temperature drift of the internal resistive divider. In general, better than 1% measurement accuracy is achievable even without calibration. The integrated resistor divider has a very low life-time drift and three different output options: delta-sigma modulator, single ended output, or differential output mode.

Figure 10-3 System Space Savings From Integrating the Resistive Divider into the TI AMC038x-Q1 Family