UCD3138128APFCR datasheet(70/83 Pages) TI1

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Voltage Loop

Filter

Vout

Loop

Mux

Ramp

Module

PCM

Comparator

Ipri

Front

End

Loop

Mux

Fault

Mux

DPWM

Loop

Mux

UCD3138128A

SLUSC99 – JULY 2016

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10.2.3.2 Peak Current Detection

Peak current detection involves all the major modules of the DPPs, the Front End, Filter, Loop Mux, Fault Mux

and the DPWMs. A drawing of the major elements is shown in Figure 48.

Figure 48. Peak Current Detection Function

All signals without arrows flow from left to right. The voltage loop is used to select a peak current level. This level

is fed to the Ramp module to generate a compensation ramp. The compensation ramp is compared to the

primary current by the PCMC comparator in the Front End. When the ramp value is greater than the primary

current, the APCMC signal is sent to the DPWM, causing the events described in the previous sections.

The DPWM frame start and output pin signals can be used to trigger the Ramp Module. In this case, unlike in the

case of other ramp module functions, each DPWM frame triggers the start of the ramp. The ramp steps every 32

ns.

The Filter is configured normally, there is no real difference for PCMC. The PCM_FILTER_SEL bits in the

LoopMux.PCMCTRL register are used to select which filter is connected to the ramp module:

LoopMuxRegs.APCMCTRL.bit.PCM_FILTER_SEL = 0; //select filter0

With Firmware Constant Power/Constant current, Filter 1 and Front End 1 are used as a current control loop,

with the EADCDAC set to high current. If the voltage loop value becomes higher than the current loop value,

then Filter 1 is used to control the PCM ramp start value:

LoopMuxRegs.APCMCTRL.bit.PCM_FILTER_SEL = 1;

//select filter1 for slope compensation source

S P A C E

In the ramp module, there are 2 bitfields in the RAMPCTRL register which must be configured. The

PCM_START_SEL must be set to a 1 to enable the Filter to be used as a ramp start source. The RAMP_EN bit

must be set, of course.

The DAC_STEP register sets the slope of the compensation ramp. The DAC value is in volts, of course, so it is

necessary to calculate the slope after the current to voltage conversion. Here is the formula for converting from

millivolts per microsecond to DACSTEP.

m = compensation slope in millivolts per microsecond

ACSTEP = 335.5 × M

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