topic Re: Fault Filter in eflexPWM in Digital Signal Controllers https://community.nxp.com/t5/Digital-Signal-Controllers/Fault-Filter-in-eflexPWM/m-p/714594#M1135 <HTML><HEAD></HEAD><BODY><P>This phenomenon is quite reasonable. The fault filter works in a way like this: there's an internal high frequency clock F_filt for detecting the input voltage level, say if the input voltage stays one&nbsp;within continuous N periods of F_filt, the input is deemed to be one. For instance, suppose the input voltage is examined at each rising edge of F_filt, and N is set to 3, now see the attached pictures, the red waveform is the input signal on fault pin, and the blue one is F_filt. Both situation 1 and 2 can pass the filter, there's an error of +/- one period of F_filt.&nbsp;</P><P><span class="lia-inline-image-display-wrapper" image-alt="fault_filter.png"><img src="https://community.nxp.com/t5/image/serverpage/image-id/42315i1F8E2BB0946966BF/image-size/large?v=v2&amp;px=999" role="button" title="fault_filter.png" alt="fault_filter.png" /></span></P><P>In the case of 8036, F_filt is 96MHz/19 = 5.05MHz, so the period of F_filt is about 0.2us, which applies to your case.&nbsp;</P></BODY></HTML> Wed, 27 Sep 2017 02:50:04 GMT sutter_zhou 2017-09-27T02:50:04Z Fault Filter in eflexPWM https://community.nxp.com/t5/Digital-Signal-Controllers/Fault-Filter-in-eflexPWM/m-p/714593#M1134 <HTML><HEAD></HEAD><BODY><P>Hello,</P><P>This is about Fault Filter in eflexPWM. Based on MC56F8036 where IPBus clock is 96MHz, PWMA_FFILTn is configured as 0x713 so filter time should be (7+3)*19/96=1.98us. But FFLAG is still set as 1 when input fault pin with a square wave&nbsp;and the width is 1.8us. Is is normal or something wrong?<A class="jx-jive-macro-user" href="https://community.nxp.com/people/sutter">sutter</A></P></BODY></HTML> Wed, 27 Sep 2017 02:27:16 GMT https://community.nxp.com/t5/Digital-Signal-Controllers/Fault-Filter-in-eflexPWM/m-p/714593#M1134 chaozhuang-b500 2017-09-27T02:27:16Z Re: Fault Filter in eflexPWM https://community.nxp.com/t5/Digital-Signal-Controllers/Fault-Filter-in-eflexPWM/m-p/714594#M1135 <HTML><HEAD></HEAD><BODY><P>This phenomenon is quite reasonable. The fault filter works in a way like this: there's an internal high frequency clock F_filt for detecting the input voltage level, say if the input voltage stays one&nbsp;within continuous N periods of F_filt, the input is deemed to be one. For instance, suppose the input voltage is examined at each rising edge of F_filt, and N is set to 3, now see the attached pictures, the red waveform is the input signal on fault pin, and the blue one is F_filt. Both situation 1 and 2 can pass the filter, there's an error of +/- one period of F_filt.&nbsp;</P><P><span class="lia-inline-image-display-wrapper" image-alt="fault_filter.png"><img src="https://community.nxp.com/t5/image/serverpage/image-id/42315i1F8E2BB0946966BF/image-size/large?v=v2&amp;px=999" role="button" title="fault_filter.png" alt="fault_filter.png" /></span></P><P>In the case of 8036, F_filt is 96MHz/19 = 5.05MHz, so the period of F_filt is about 0.2us, which applies to your case.&nbsp;</P></BODY></HTML> Wed, 27 Sep 2017 02:50:04 GMT https://community.nxp.com/t5/Digital-Signal-Controllers/Fault-Filter-in-eflexPWM/m-p/714594#M1135 sutter_zhou 2017-09-27T02:50:04Z