DSPIC33FJ06GS201TESLASHMM datasheet(262/346 Pages) MICROCHIP

262 / 346 page

dsPIC33FJ06GS101/X02 and dsPIC33FJ16GSX02/X04

DS70318D-page 260

Preliminary

20.3

Module Applications

This module provides a means for the SMPS dsPIC

DSC devices to monitor voltage and currents in a

power conversion application. The ability to detect

transient conditions and stimulate the dsPIC DSC

processor and/or peripherals, without requiring the

processor and ADC to constantly monitor voltages or

currents, frees the dsPIC DSC to perform other tasks.

The comparator module has a high-speed comparator

and an associated 10-bit DAC that provides a

programmable reference voltage to the inverting input

of the comparator. The polarity of the comparator out-

put is user-programmable. The output of the module

can be used in the following modes:

• Generate an Interrupt

• Trigger an ADC Sample and Convert Process

• Truncate the PWM Signal (current limit)

• Truncate the PWM Period (current minimum)

• Disable the PWM Outputs (Fault latch)

The output of the comparator module may be used in

multiple modes at the same time, such as: (1)

generate an interrupt, (2) have the ADC take a sample

and convert it, and (3) truncate the PWM output in

response to a voltage being detected beyond its

expected value.

The comparator module can also be used to wake-up

the system from Sleep or Idle mode when the analog

input voltage exceeds the programmed threshold

voltage.

20.4

DAC

The range of the DAC is controlled via an analog

multiplexer that selects either AVDD/2, internal 1.2V,

1% reference, or an external reference source,

EXTREF. The full range of the DAC (AVDD/2) will

typically be used when the chosen input source pin is

shared with the ADC. The reduced range option

(INTREF) will likely be used when monitoring current

levels using a current sense resistor. Usually, the

measured voltages in such applications are small

(<1.25V); therefore the option of using a reduced

reference range for the comparator extends the

available DAC resolution in these applications. The

use of an external reference enables the user to

connect to a reference that better suits their

application.

DACOUT, shown in Figure 20-1, can only be

associated with a single comparator at a given time.

20.5

Interaction with I/O Buffers

If the comparator module is enabled and a pin has

been selected as the source for the comparator, then

the chosen I/O pad must disable the digital input buffer

associated with the pad to prevent excessive currents

in the digital buffer due to analog input voltages.

20.6

Digital Logic

The CMPCONx register (see Register 20-1) provides

the control logic that configures the comparator

module. The digital logic provides a glitch filter for the

comparator output to mask transient signals in less

than two instruction cycles. In Sleep or Idle mode, the

glitch filter is bypassed to enable an asynchronous

path from the comparator to the interrupt controller.

This asynchronous path can be used to wake-up the

processor from Sleep or Idle mode.

The comparator can be disabled while in Idle mode if

the CMPSIDL bit is set. If a device has multiple

comparators, if any CMPSIDL bit is set, then the entire

group of comparators will be disabled while in Idle

mode. This behavior reduces complexity in the design

of the clock control logic for this module.

The digital logic also provides a one TCY width pulse

generator for triggering the ADC and generating

interrupt requests.

The CMPDACx (see Register 20-2) register provides

the digital input value to the reference DAC.

If the module is disabled, the DAC and comparator are

disabled to reduce power consumption.

20.7

Comparator Input Range

The comparator has a limitation for the input Common

Mode Range (CMR) of (AVDD – 1.5V), typical. This

means that both inputs should not exceed this range.

As long as one of the inputs is within the Common

Mode Range, the comparator output will be correct.

However, any input exceeding the CMR limitation will

cause the comparator input to be saturated.

If both inputs exceed the CMR, the comparator output

will be indeterminate.

20.8

DAC Output Range

The DAC has a limitation for the maximum reference

voltage input of (AVDD – 1.6) volts. An external

reference voltage input should not exceed this value or

the reference DAC output will become indeterminate.

20.9

Comparator Registers

The comparator module is controlled by the following

registers:

• CMPCONx: Comparator Control Register

• CMPDACx: Comparator DAC Control Register

Note:

It should be ensured in software that

multiple DACOE bits are not set. The

output on the DACOUT pin will be indeter-

minate if multiple comparators enable the

DAC output.

DSPIC33FJ06GS201TE/MM Datasheet(PDF) 262 Page - Microchip Technology

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