JAJSHC9B May 2019 – October 2021 ALM2402F-Q1
The resolver primary winding or excitation coil can be driven by a single-ended op amp output with the other side of the coil grounded, or differentially as shown in Figure 8-2. A differential drive offers higher voltage (double) on to the excitation coil, while not using as much output voltage headroom from the op amp. This larger output voltage due to the differential drive leads to lower distortion on the output signal.
For this example, the resolver impedance is specified from 2 VRMS and 7 VRMS up to 20-kHz maximum frequency. To highlight use with a 7 VRMS resolver, an excitation voltage of 10 VPP is applied from each channel of the ALM2402F-Q1. The op amp is set in an inverting gain = –2 V/V, while applying an adequate common-mode bias. These conditions give the required 7 VRMS differential output (3.5 VRMS per each op amp channel) to the resolver primary winding without running into any op-amp headroom issues.
Another consideration for excitation is op-amp power dissipation. As described in the Power Dissipation and Thermal Reliability section, power dissipation from the op amp can be lowered by driving the output peak voltages close to the supply and ground voltages. With the very low VOH/VOL of the ALM2402F-Q1, lower power dissipation is easily accomplished. See the Output Stage section for a further description of the rail-rail output stage.