8.2.2.4 Current Sense Amplifiers

The DRV8305-Q1 provides three bidirectional low-side current shunt amplifiers. These can be used to sense the current flowing through each half-bridge. If individual half-bridge sensing is not required, a single current shunt amplifier can be used to measure the sum of the half-bridge current. Use this simple procedure to correctly configure the current shunt amplifiers.

1. Determine the peak current that the motor will demand (IMAX). This demand depends on the motor parameters and the application requirements. IMAX in this example is 14 A.
2. Determine the available voltage output range for the current shunt amplifiers. This will be the ± voltage around the amplifier bias voltage (VBIAS). In this case VBIAS = 1.65 V and a valid output voltage is 0 to 3.3 V. This gives an output range of ±1.65 V.
3. Determine the sense resistor value and amplifier gain settings. The sense resistor value and amplifier gain have common tradeoffs. The larger the sense resistor value, the better the resolution of the half-bridge current. This comes at the cost of additional power dissipated from the sense resistor. A larger gain value allows for the use of a smaller resolution, but at the cost of increased noise in the output signal and a longer settling time. This example uses a 5-mΩ sense resistor and the minimum gain setting of the DRV8305-Q1 (10 V/V). These values allow the current shunt amplifiers to measure ±33 A across the sense resistor.