MCP3464T-ESLASHST datasheet(37/108 Pages) MICROCHIP

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DS20006180D-page 37

MCP3461/2/4

FIGURE 5-3:

MDAT Serial Outputs in

Function of the Modulator Output Code.

5.4.3

BOOST MODES

The Delta-Sigma modulator includes a programmable

biasing circuit in order to further adjust the power

consumption to the sampling speed applied through

the MCLK. This can be programmed through the

BOOST[1:0] bits in the CONFIG2 register. The

different BOOST settings are applied to the whole

modulator circuit, including the voltage reference

buffers. The settings of the BOOST[1:0] bits are

described in Table 5-5.

The maximum achievable Analog Master Clock (AMCLK)

speed, the maximum sampling frequency (DMCLK)

and the maximum achievable data rate (DRCLK) are

highly dependent on the BOOST[1:0] and GAIN[2:0]

settings. A higher BOOST setting will allow the circuits’

bandwidth to be increased and will allow a higher

analog master clock rate that will then increase the

baseband of the input signals to be converted. The

digital gain (that is enabled at 32x and 64x gains) has

no influence on the achievable bandwidth.

A typical dependency of the bandwidth in relation to the

GAIN for each BOOST setting combination is shown in

Figure 2-20 to Figure 2-23. Typically, a larger GAIN

setting requires a higher BOOST setting in order to

achieve the same bandwidth performance.

Figure 2-24 shows the behavior of the achievable

bandwidth at BOOST = 1x with AVDD corner cases.

Since the BOOST settings vary, the internal slew rate

of the modulator components using a lower VREF value

will improve the bandwidth if low BOOST settings are

used and are showing a limited bandwidth behavior.

TABLE 5-4:

DELTA-SIGMA MODULATOR

OUTPUT BIT STREAM CODING

COMP[3:0]

Code

Modulator

Output Code

(Decimal)

MDAT

Serial

Stream

Equivalent

VREF

Voltage

1111

+VREF

0111

+VREF/2

0011

0001

-1

0001

-VREF/2

0000

-2

0000

-VREF

AMCLK

tDOMDAT

MDAT

(code = +2)

MDAT

(code = +1)

MDAT

(code = 0)

MDAT

(code = -1)

MDAT

(code = -2)

COMP[3]

C OMP[2]

COMP[1]

C OMP[0]

tDOMDAT tDOMDAT tDOMDAT tDOMDAT

TABLE 5-5:

BOOST SETTINGS

DESCRIPTION

BOOST[1:0]

Bias Current

x0.5

x0.66

x1 (default)

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