TIDA-01168: Poles&Zero compensation strategy for digital outer voltage control loop
Part Number: TIDA-01168
We have stability issues with our converter which is based on the TIDA-01168. What is the correlation between the coefficients used in the software (Buck mode shown below) and the LM5170 design calculator? What parameters were entered in the LM5170 calculator to obtain these coefficients?
/* Buck mode digital compensation constants */#define B0_BUCK (2.602812)// (0.443017) /* B0 constant */#define B1_BUCK (0.040566)//(0.264689) /* B1 constant */#define B2_BUCK (-2.562246)// (-0.17832) /* B2 constant */#define A1_BUCK (0.918233)// (0.466008) /* A1 constant */#define A2_BUCK (0.081767)// (0.533991) /* A2 constant */
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I asked the product line for help with this request. It has been a while since I worked on the design and I need to refresh what I did there three years ago.
You should first investigate if the inner current loop is stable. This is easily done using an electronic load operating in constant resistance mode and keeping the voltage on the ISET pin constant (e.g. pushing 12A to the load set to 1ohm). The current loop must be stable and the step response has to be free of overshoots.
I believe the most complete answer is available in this excellent videotraining from Garrett Roecker:
Alternatively, some materials from Biricha power are available:
Starting from the slide 36 the document discusses how to get the linear differential equation from the analog transfer function.
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