MCP3912 datasheet(38/82 Pages) MICROCHIP

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MCP3912

DS20005348A-page 38

 2014 Microchip Technology Inc.

The PHASE register is split into two 12-bit banks that

represent the delay between each pair of channels.

The equivalence is defined in Table 5-8. Each phase

value (PHASEA/B) represents the delay of the even

channel with respect to the associated odd channel

with an 11-bit plus sign, MSB-first two's complement

code. This code indicates how many DMCLK periods

there are between each channel in the pair. (see

Equation 5-5). Since the odd channels are the time

reference, when PHASEX<11:0> is positive, the even

channel of the pair is lagging and the odd channel is

leading. When PHASEX<11:0> is negative, the even

channel of the pair is leading and the odd channel is

lagging.

EQUATION 5-5:

The timing resolution of the phase delay is 1/DMCLK or

1 µs in the default configuration with MCLK = 4 MHz.

Given the definition of DMCLK, the phase delay is

affected by a change in the prescaler settings

(PRE<1:0>) and the MCLK frequency.

The data ready signals are affected by the phase delay

settings. Typically, the time difference between the data

ready pulses of odd and even channels is equal to the

associated phase delay setting.

Each ADC conversion start and, therefore, each data

ready pulse is delayed by a timing of OSR/2 x DMCLK

periods (equal to half a DRCLK period). This timing

allows for the odd channel’s data ready signals to be

located at a fixed time reference (OSR/2 x DMCLK

periods from the reset) while the even channel can be

leading or lagging around this time reference with the

corresponding PHASEX<11:0> delay value.

5.9.1

PHASE DELAY LIMITS

The limits of the phase delays are determined by the

OSR settings: the phase delays can only go from

-OSR/2 to +OSR/2-1 DMCLK periods.

If larger delays between the two channels are needed,

they can be implemented externally to the chip with an

MCU. A FIFO in the MCU can save incoming data from

the leading channel for a number N of DRCLK clocks.

In this case, DRCLK would represent the coarse timing

resolution, and DMCLK the fine timing resolution. The

total delay will then be equal to:

EQUATION 5-6:

The Phase delay registers can be programmed once

with the OSR = 4096 setting, and will adjust the OSR

automatically afterwards without the need to change

the value of the phase registers.

• OSR = 4096

: The delay can go from -2048 to

+2047. PHASEX<11> is the sign bit.

PHASEX<10> is the MSB and PHASEX<0> the

LSB.

• OSR = 2048

: The delay can go from -1024 to

+1023. PHASEX<10> is the sign bit. PHASEX<9>

is the MSB and PHASEX<0> the LSB.

• OSR = 1024

: The delay can go from -512 to +511.

PHASEX<9> is the sign bit. PHASEX<8> is the

MSB and PHASEX<0> the LSB.

•OSR = 512

: The delay can go from -256 to +255

PHASEX<8> is the sign bit. PHASEX<7> is the

MSB and PHASEX<0> the LSB.

• OSR = 256: The delay can go from -128 to +127.

PHASEX<7> is the sign bit. PHASEX<6> is the

MSB and PHASEX<0> the LSB.

• OSR = 128: The delay can go from -64 to +63.

PHASEX<6> is the sign bit. PHASEX<5> is the

MSB and PHASEX<0> the LSB.

• OSR = 64: The delay can go from -32 to +31.

PHASEX<5> is the sign bit. PHASEX<4> is the

MSB and PHASEX<0> the LSB.

• OSR = 32: The delay can go from -16 to +15.

PHASEX<4> is the sign bit. PHASEX<3> is the

MSB and PHASEX<0> the LSB.

TABLE 5-8:

PHASE DELAYS

EQUIVALENCE

Pair of

channels

Phase Bank

Position

CH1/CH0

PHASEA<11:0>

PHASE<11:0>

CH3/CH2

PHASEB<11:0>

PHASE<23:12>

Note:

For a detailed explanation of the Data

Ready pin (DR) with phase delay, see

Section 5.11 “Data Ready Status Bits”

Total Delay

PHASEX<11:0> Decimal Code

DMCLK

-----------------------------------------------------------------------------------

where: X = A/B

Note:

Rewriting the PHASE registers with the

same value automatically resets and

restarts all ADCs.

Total Delay = N/DRCLK + PHASE/DMCLK

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