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AMC1304M25 Delta Sigma Modulator and TMS320F28377S SDFM

Other Parts Discussed in Thread: TMS320F28377S, CONTROLSUITE


I am using Sigma Delta Modulator 1304M25 and related digital filter SDFM from TMS320F28377S to measure the currents/ voltages of inverter in automotive applications.

The TI example that i used for this is controlsuite\...\sdfm_sync_cpu_cpu01 with following settings


Input control Mode: Mode0

Comparator: COSR_32, Sinc3

Data Filter channel 1: DOSR_256, Sinc3, Data output 16-Bit, Shift Bits_9

Interrupts Activated: MFIE (modulator clock Fail), AFx (Filter Acknowledge interrupts), Under-Current Threshold ( IEL ), Over-Current Threshold ( IEH )

External Filter Reset (FILRES): Disabled, Filter Data Rate = Modulator Data Rate (10Mhz) / DOSR (256) = 39,1KSPS and Latency = SINC3 / Filter Data Rate = 76,8uS

Clock Frequency: 10Mhz, Same clock signal feeds SDFM and SD-Modulator

Modulator Data update on each CLK falling edge.

SDFM data strobing at each CLK rising edge.

SDFM ISR Routine reads data on each Acknowledge Interrupt.

1) I want to know the permitted frequency range of analog input AINP, AINN to delta sigma modulator? I am getting a nice Sine wave at Filter output with analog input having frequency 1KHz, but as soon as I increase the analog input signal freuqncy from 1 KHz to 5 KHz or 10KHz, the results get worse and I can't see a sine wave anymore. I tried increasing Clock frequency to 20MHz but it didn't help. Could someone please tell me where do I stilll lack?

Below both of outputs at input frequency of 1KHz and 10KHz

a) Analog signal: Vpp 100mV, 1 KHz, CLK 10 MHz

b) Analog Signal: 100mV Vpp, Input Frequency 10KHz, Clock 20MHz

Thank you for your help in advance.

Best Regards,