Datasheet

TMC4671 Datasheet • IC Version V1.3 | Document Revision V2.00 • 2020-Apr-17
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4.4.16 External Delta Sigma Modulator Interface
The TMC4671 is equipped with integrated digital filters for extraction of ADC raw values from delta sigma
data stream for both internal and external delta sigma modulators. The interface for external delta sigma
modulators is intended for external isolated sigma delta modulators, such as AD7401 (with MCLK input
driven by TMC4671), or AD7402 (with MCLK output to drive TMC4671). In addition, the external delta sigma
interface supports the use of simple comparator with a R-C-R network as external low cost delta sigma
modulators (R-C-R-CMP, e.g. LM339).
Info
When selecting the external delta sigma ADC Interface, the high-performance
Debug SPI Interface (RTMI) it not available in parallel due to pin sharing. The UART
is always available, but with less performance than the RTMI.
Each external delta sigma modulator channel (dsMOD) has two signals (pls. refer figure 17), one dedicated
input, and one programmable input/output. The configuration of the external delta sigma modulator
interface is defined by programming associated registers. When selecting external delta signal ADC, the
associated analog ADC inputs are configured as digital inputs for the delta sigma signal data stream MDAT.
4.4.16.1 External Delta Sigma Modulator Interface - MDAC Configuration
Figure 18: ∆Σ ADC Configuration - MDAC (Comparator-R-C-R as ∆Σ-Modulator)
In the MDAC delta sigma modulator, the delay of the comparator CMP determines the MCLK of the
comparator modulator. A capacitor C
MCCM P
within a range of 100 pF . . . 1nF fits in most cases. The time
constant τ RC should be in a range of 0.1 tCMP . . . tCMP of the comparator. The resistors should be in the
range of 1K to 10K. The fMAXtyp depends also on the choice of the decimation ratio.
CMP tCMPtyp [ns] R
MCMP
[kΩ] R
MDAC
[kΩ] C
MCMP
[pF ] fMCLKmaxTYP
LM339 1000 1 1 100 1 MHz
LM339 1000 10 10 100 100 kHz
LM339 1000 100 100 100 10 kHz
Table 15: Delta Sigma R-C-R-CMP Configurations (pls. refer 17)
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