UCD3138RMHT.A datasheet(66/99 Pages) TI2

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In addition, it is necessary to set the D2S_COMP_EN bit in the EADCCTRL register. This is for enabling the

differential to single ended comparator function. The front end diagram leaves it out for simplicity, but the

connection between the DAC and the EADC amplifier is actually differential. The PCMC comparator, however, is

single ended. So a conversion is necessary as shown in Figure 10-9.

EAP0

EAN0

DAC0

EADC

4 bit dithering gives 14 bits of effective resolution

97.65625μV/ LSB effective resolution

6 bit ADC

8mV/LSB

Signed 9 bit result

(error) 1 mV /LSB

AFE_GAIN

10 bit DAC

1. 5625mV/ LSB

Value

Dither

CPCC

Filter x

Ramp

SAR/ Prebias

Absolute Value

Calculation

Averaging

10 bit result

1.5625mV/LSB

3-AFE_GAIN

Peak Current Mode

Comparator

Peak Current

Detected

Differential to

Single Ended

AFE_GAIN

Figure 10-9. Differential to Single-Ended Comparator Function

The EADC_MODE bit in EADCCTRL should be set to a 5 for peak current mode.

The peak current detection signal next goes to the Loop Mux. The Fault Mux has only 1 APCM input, but there

are 3 front ends. So the PCM_FE_SEL bits in APCMCTRL must be used to select which front end is used:

LoopMuxRegs.APCMCTRL.bit.PCM_FE_SEL = 2; // use FE2 for PCM */

The PCM_EN bit must also be set.

LoopMuxRegs.APCMCTRL.bit.PCM_EN = 1; // Enable PCM

Next the Fault Mux is used to enable the APCM bit to the CLIM/CBC signal to the DPWM. There are 4

DPWMxCLIM registers, one for each DPWM. The ANALOG_PCM_EN bit must be set in each one to connect

the PCM detection signal to the CLIM/CBC signal on each DPWM. For the latest configuration information on all

of these bits, consult the appropriate EVM firmware. To avoid errors, it is best to configure your hardware design

using the same DPWMs, filters, and front ends for the same functions as the EVM.

DPWM timing is used to trigger the start of the ramp. This is selected by the FECTRLxMUX registers in the

Loop Mux. DPWMx_FRAME_SYNC_EN bits, when set, cause the ramp to be triggered at the start of the DPWM

period.

10.2.2.6.3 Peak Current Mode (PCM)

There is one peak current mode control module in the device however any front end can be configured to use

this module.

UCD3138

SLUSAP2J – MARCH 2012 – REVISED NOVEMBER 2021

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