Hi team,
My customer is using the DRV8818EVM to do evaluation. They have found one issue when using,
The output current they need is 1.7A. According to the formula, the reference voltage should be set to 1.3V. But in real test, they find the output current is not 1.7A, and will change frequently.
Can you help see what's the problem? Also, customer wants to know how to choose the decay mode? Pls kindly let me know your suggestions.
Regards,
Xiaoying
Hi Xiaoying,
Please refer to the table below for assistance in selecting a decay mode.
| Slow Decay | Fast Decay | Mixed Decay | |
|
Ripple Magnitude |
Low Best with low inductance motors |
High Good for high inductance motors |
Medium |
|
Off-time |
Long Might lead to audible noise |
Short May lead to excessive switching losses |
Medium Best tradeoff between frequency |
|
Decreasing steps |
Slow Distortion observed in sinusoid waveform |
Fast Best for decreasing steps |
Fast Good for decreasing steps |
In essence, it depends on the kind of motor used and the performance required. Mixed decay is the best tradeoff amongst the three. Hope this helps.
About the output current changing frequently, can you please share some waveforms? I would like to understand what is meant by 'change frequently'. Current ripples are expected in all decay modes. Please refer to this video and this app report for more details on decay modes' operation.
Based on the formula, the Vref value required for 1.7A is 1.36V, which when approximated is close to 1.4V. Please adjust the slider slightly to the right to obtain 1.7A.
