The SDFM is a 4-channel digital filter designed specifically for current measurement and resolver position decoding in motor control applications. Each channel can receive an independent sigma-delta (ΣΔ) modulated bit stream. The bit streams are processed by four individually programmable digital decimation filters. The filter set includes a fast comparator for immediate digital threshold comparisons for overcurrent and undercurrent monitoring.
The SDFM features include:
- 8 external pins per SDFM module
- 4 sigma-delta data input pins per SDFM module (SDx_D1-4)
- 4 sigma-delta clock input pins per SDFM module (SDx_C1-4)
- 4 different configurable modulator clock modes:
- Mode 0: Modulator clock rate equals modulator data rate
- Mode 1: Modulator clock rate running at half the modulator data rate
- Mode 2: Modulator data is Manchester encoded. Modulator clock not required.
- Mode 3: Modulator clock rate is double that of modulator data rate
- 4 independent configurable secondary filter (comparator) units per SDFM module:
- 4 different filter type selection (Sinc1/Sinc2/Sincfast/Sinc3) options available
- Ability to detect over-value, under-value, and zero-crossing conditions
- OSR value for comparator filter unit (COSR) programmable from 1 to 32
- 4 independent configurable primary filter (data filter) units per SDFM module:
- 4 different filter type selection (Sinc1/Sinc2/Sincfast/Sinc3) options available
- OSR value for data filter unit (DOSR) programmable from 1 to 256
- Ability to enable individual filter modules
- Ability to synchronize all the 4 independent filters of an SDFM module using Master Filter Enable (MFE) bit or using PWM signals
- Data filter unit has programmable FIFO to reduce interrupt overhead. FIFO has the following features:
- Primary filter (data filter) has 16 deep × 32-bit FIFO
- FIFO can interrupt CPU after programmable number of data ready events
- FIFO Wait-for-Sync feature: Ability to ignore data ready events until PWM synchronization signal (SDSYNC) is received. Once SDSYNC event is received, FIFO is populated on every data ready event
- Data filter output can be represented in either 16 bits or 32 bits
- PWMx.SOCA/SOCB can be configured to serve as SDSYNC source on per data filter channel basis
- PWMs can be used to generate a modulator clock for sigma delta modulators
Note: Care should be taken to avoid noise on the SDx_Cy input. If the minimum pulse width requirements are not met (for example, through a noise glitch), then the SDFM results could become undefined.
Figure 7-73 shows the SDFM block diagram.