DRV10983: Calculating Efficiency DRV10983 BLDC driver

Hello Boopathi,

When I hear "Controller efficiency" I'm going to assume we are comparing the power delivered to the motor and power consumed by the controller that doesn't directly contribute to the motion of the motor. 

Calculating power delivered to motor:

The equation for power delivered to motor depends on the Voltage exposed to the motor and the RMS phase Current that flows through the motor as a result. This also depends on the user's input duty cycle % (or speed command %).

P (Watts) = PWM_DCO%  *  Supply Voltage (V) * Phase Current I rms  

More information can be found in this E2E post: http://e2e.ti.com/support/motor-drivers/f/38/p/735527/2715263#2715263 

Calculating power consumed by controller:

This is determined by power disipated through RDS(ON), switching losses, operating supply current operation, and other sources of power dissipation (such as the DRV10983's LDO or VREG).

PD = P_RDS + P_SW + P_IVM + P_LDO

The equations and an example calculation can be found in the "How to Design a Thermally-Efficient Integrated BLDC Motor Drive PCB" App note: http://www.ti.com/lit/an/slva938a/slva938a.pdf 

Comments:

Calculating power consumed by the controller will have some error because many of the equations rely on datasheet values or parameters that are not very easy to measure. While you could measure some of them for a particular device, there will be some variance from device to device. This means, the calculations are approximations. As a result, using equipment that can measure current and voltage (such as a power network analyzer) will give you a more accurate result.

Best,

-Cole