MCP3551-ESLASHMS datasheet(14/30 Pages) MICROCHIP

14 / 30 page

MCP3550/1/3

DS21950D-page 14

FIGURE 4-2:

SINC Filter Response,

MCP3550-50 Device.

FIGURE 4-3:

SINC Filter Response,

MCP3550-60 Device.

FIGURE 4-4:

SINC Filter Response,

MCP3551 Device, Simultaneous 50/60 Hz

Rejection.

FIGURE 4-5:

SINC Filter Response at

Integer Multiples of the Sampling Frequency (fs).

4.3

Internal Oscillator

The MCP3550/1/3 devices include a highly stable and

accurate internal oscillator that provides clock signals

to the delta-sigma ADC with minimum jitter. The oscil-

lator is a specialized structure with a low temperature

coefficient across the full range of specified operation.

See Table 4-1 for oscillator frequencies.

The conversion time is an integer multiple of the inter-

nal clock period and, therefore, has the same accuracy

as the internal clock frequency. The internal oscillator

frequency is 102.4 kHz ±1% for the MCP3550-50,

112.64 kHz ±1% for the MCP3551, and 122.88 kHz

±1% for the MCP3550-60 and MCP3553 devices,

across the full power supply voltage and specified

temperature ranges.

The notch of the digital filter is proportional to the

internal oscillator frequency, with the exact notch

frequency equivalent to the oscillator accuracy (< 1%

deviation). This high accuracy, combined with wide

notches, will ensure that the MCP3551 will have simul-

taneous 50 Hz and 60 Hz line frequency rejection and

the MCP3550-50 or MCP3550-60 devices will have

greater than 120 dB rejection (at either 50 or 60 Hz) by

the digital filtering, even when jitter is present.

The internal oscillator is held in the reset condition

when the part is in Shutdown mode to ensure very low

power consumption (< 1 µA in Shutdown mode). The

internal oscillator is independent of all serial digital

interface edges (i.e., state machine processing the

digital SPI interface is asynchronous with respect to the

internal clock edges).

-120

-100

-80

-60

-40

-20

100

150

200

Frequency (Hz)

-120

-100

-80

-60

-40

-20

120

180

240

Frequency (Hz)

-120

-110

-100

-90

-80

-70

-60

-50

-40

-30

-20

-10

102030

60708090 100 110

Frequency (Hz)

-140

-120

-100

-80

-60

-40

-20

28160

56320

84480 112640 140800 168960 197120 225280 253440

Frequency (Hz)

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