High Current Driver for AD2S1210 Resolver Digital Reference Signal Output

Circuit Functionality and Benefits

Resolver-to-digital converters (RDCs) are widely used in automotive and industrial applications to provide motor shaft position/velocity feedback information.

The AD2S1210 is a complete 10-bit to 16-bit resolution RDC with an on-chip programmable sine wave oscillator to provide resolver excitation. Due to the harsh operating environment, the AD2S1210 (C and D grades) is rated over the extended industrial temperature range of -40°C to +125°C.

The high current driver shown in Figure 1 amplifies and level-shifts the reference oscillator output of the AD2S1210 to optimize the interface with the resolver. The driver is a composite amplifier using the dual-channel, low-noise, precision AD8662 operational amplifier and a discrete complementary emitter follower output stage. A similar driver stage is used for the complementary excitation outputs, providing a fully differential signal to drive the resolver primary winding. The AD8662 is available in 8-lead narrow-body SOIC and 8-lead MSOP packages, both rated over the extended industrial temperature range of -40°C to +125°C.

RDCs are used in conjunction with rotation sensors to detect the position and speed of the motor shaft. In this application, the resolver is excited with a sinusoidal reference signal. The resolver excitation reference signal on the primary winding is converted into two sinusoidal differential output signals: sine and cosine. The amplitude of the sine and cosine signals depends on the actual resolver position, the resolver conversion ratio, and the excitation signal amplitude.

The RDC samples the two input signals synchronously to provide digitized data to the digital engine, the so-called Type II tracking loop. The Type II tracking loop is responsible for calculating the position and speed. A typical application circuit is shown in Figure 2.

Depending on the resolver input signal requirements, the excitation buffer must provide up to 200 mA of single-ended current. The buffer circuit shown in Figure 1 not only provides current drive capability, but also provides gain to the AD2S1210 excitation output signal. This circuit note describes the performance requirements and recommended excitation buffer topology. Typical resolver input resistance is between 100 Ω and 200 Ω, and the primary coil should be driven with a voltage of 7 V RMS.

The converter supports input signals in the range of 3.15 V pp ±27%. The AD2S1210 is rated for a frequency range of 2 kHz to 20 kHz. A Type II tracking loop is used to track the input signal and convert the information at the sine and cosine inputs into digital quantities corresponding to the input angle and velocity. The device is rated for a maximum tracking rate of 3 125 r/s. At 16-bit resolution, the maximum accuracy error of the position output is ±5.3 arc minutes.

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