MCP3461RT-ESLASHST datasheet(56/118 Pages) MICROCHIP

56 / 118 page

MCP3461/2/4R

DS20006404C-page 56

 2020-2021 Microchip Technology Inc.

FIGURE 5-11:

ADC Start-up Timer Timing Diagram.

5.12

Master Clock Selection/Internal

Oscillator

The device includes three possible clock modes for the

master clock generation. The Master Clock (MCLK) is

used by the ADC to perform conversions and is also used

by the digital portion to generate the different digital

timers. The clock mode selection is made through the

CLK_SEL[1:0] bits located in the CONFIG0 register. The

possible selections are described in Table 5-13.

The master clock is not propagated in the chip when the

chip enters the Full Shutdown mode (see Section 5.10

“Low-Power Shutdown Modes”). Any change to the

CLK_SEL bits creates a Reset and Restart for the

currently running conversions, and a Restart of the ADC

setup timer. Each Reset and Restart resets all internal

phases to their default values and can lead to a possible

temporary duty cycle change at the clock output pin.

TABLE 5-13:

CLOCK SELECTION BITS

5.12.1

EXTERNAL MASTER CLOCK MODE

(CLK_SEL[1:0] = 0x)

The External Clock mode is used to input the MCLK

clock necessary for the ADC conversions and can

accept duty cycles with a large range since the clock is

redivided internally to generate the different internal

phases.

The external clock can be provided on the MCLK pin for

the MCP3461/2/4R devices.

5.12.2

INTERNAL OSCILLATOR

The device includes an internal RC-type oscillator

frequency of this internal oscillator ranges from

3.3 MHz to 6.6 MHz. The oscillator is not trimmed in

production, therefore, the precision of the center

frequency is approximately ±30% from chip to chip.

The duty cycle of the internal oscillator is centered

around 50% and varies very slightly from chip to chip.

The internal oscillator has no Reset feature and keeps

running once selected.

ADC Start-up

Timer Decimal

Code

ADC_MODE

DMCLK

256

Continuous Clocking

Switching Between ADC_MODE = 10 and 11

has no Effect on the Timer

Timer Reset

ADC Ready to Convert

SPI

Write

ADC_M ODE = 1x

Write

AD C_M ODE = 0x

Wri te

ADC _M ODE = 1x

Write

ADC_M ODE = 1x

Timer Reset

Timer

Countdown

CLK_SEL[1:0]

Clock Mode

MCLK Pin

00 or 01

External Clock

MCLK digital input

Internal RC

Oscillator,

no clock output

High-Z

Internal RC

Oscillator with

clock output

AMCLK digital

output

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