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Sheet目录3871

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2006 Microchip Technology Inc.

Preliminary

DS70178C-page 181

dsPIC30F1010/202X

16.4

ADC Result Buffer

The ADC module contains up to 12 data output regis-

ters to store the A/D results called ADCBUF<11:0>.

The registers are 10 bits wide, but are read into differ-

ent format, 16-bit words. The buffers are read-only.

Each analog input has a corresponding data

output register.

This module DOES NOT include a circular data

buffer or FIFO. Because the conversion results may

be produced in any order, such schemes will not work

since there would be no means to determine which

data is in a specific location.

The SAR write to the buffers is synchronous to the

ADC clock. Reads from the buffers will always have

valid data assuming that the data-ready interrupt has

been processed.

If a buffer location has not been read by the software

and the SAR needs to overwrite that location, the

previous data is lost.

Reads from the result buffer pass through the data for-

matter. The 10 bits of the result data are formatted into

a 16-bit word.

16.5

Application Information

The ADC module implements a concept based on

“Conversion Pairs”. In power conversion applications,

there is a need to measure voltages and currents for

each PWM control loop. The ADC module enables the

sample and conversion process of each conversion

pair to be precisely timed relative to the PWM signals.

In a user’s application circuit, the PWM signal enables

a transistor, which allows an inductor to charge up with

current to a desired value. The longer a PWM signal is

on, the longer the inductor is charging, and therefore

the inductor current is at its maximum at the end of the

PWM signal. Often, this is the point where the user

wants to take the current and voltage measurements.

Figure 16-2 shows a typical power conversion applica-

tion (a boost converter) where the current sensing of

the inductor is done by monitoring the voltage across a

resistor in series with the power transistor that

“charges” the inductor. The significant feature of this

figure is that if the sampling of the resistor voltage

occurs slightly later than the desired sample point, the

data read will be zero. This is not acceptable in most

applications. The ADC module always samples the

analog voltages at the appointed time regardless of

whether the ADC converter is busy or not.

The Power Supply PWM module supports 2-4 indepen-

dent PWM channels as well as 2-4 trigger signals (one

per PWM generator). The user can configure these

channels to initiate an ADC conversion of a selected

input pair at the proper time in the PWM cycle. The

Power Supply PWM module also provides an addi-

tional trigger signal (Special Event Trigger), which can

be programmed to occur at a specified time during the

primary time base count cycle.

FIGURE 16-2:

APPLICATION EXAMPLE: IMPORTANCE OF PRECISE SAMPLING

PWM

Late sample yields

zero data

Desired sample point

Critical Edge

+VIN

PWM

VISENSE

VOUT

COUT

Measuring peak inductor current is very important

Example Boost Converter

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