SPRUJ53B April 2024 – September 2024 TMS320F28P550SJ , TMS320F28P559SJ-Q1
The internal DAC's reference voltage source, DACREF, is set to VREFHI. The x2 gain mode is only available when VREFHI is set as DACREF and internal reference mode is used, which can be configured by DACCTL[MODE] register. The internal reference circuit generates 1.65V and 2.5V. To select either 2.5V or 1.65V, configure ANAREFx1P65SEL register and set ANAREFPCTL[REFPMUXSELx] register to 0 (see the Analog Subsystem chapter on how to switch to internal reference mode). Even though the buffered DAC has an x2 gain mode, the maximum output voltage from the buffered DAC is not greater than VDDA. Table 16-1 lists the gain mode combinations supported by the buffered DAC. In this table, x = A or B, X = Don't Care, VREFHI = 2.5v, VDDA = 3.3v, and DACVAL = 4095.
DACREFSEL | ANAREFPCTL[REFPMUXSELx] | ANAREFx1P65SEL | Reference Source | Reference Voltage (V) | Mode | Maximum DAC Output (V) | Support Status |
---|---|---|---|---|---|---|---|
1 | 0 | 0 | Internal | 1.65 | 0 | 1.65 | Not Supported |
1 | 0 | 0 | Internal | 1.65 | 1 | 3.3 | Supported |
1 | 0 | 1 | Internal | 2.5 | 0 | 2.5 | Supported |
1 | 0 | 1 | Internal | 2.5 | 1 | 2.5 | Not Supported |
1 | 1 | X | External | VREFHI | 0 | 2.5 | Supported |
1 | 1 | X | External | VREFHI | 1 | 2.5 | Not Supported |
Two sets of DACVAL registers, DACVALA and DACVALS, are present in the buffered DAC module. DACVALA is a read-only register that actively controls the buffered DAC value. DACVALS is a writable shadow register that loads into DACVALA either immediately or synchronized with the next EPWMSYNCPER event. If the clock to the buffered DAC is disabled while the buffered DAC is outputting a voltage, the output voltage remains unaffected, but DACVALA and DACVALS is no longer updated with register writes. Enabling the clock to the buffered DAC restores the DAC to the state before the clock was disabled.
The output of the internal DAC is calculated with the following equation:
The buffered DAC can be used to level-shift the PGA input signal (see the Programmable Gain Amplifier (PGA) chapter for details). The output buffer of the buffered DAC can exhibit non-linear behavior near the supply rails (VDDA/VSSA). To determine the linear range of the buffered DAC, see the device-specific data sheet.