Microchip Technology MCP355XDV-MS1 Data Sheet

© 2009 Microchip Technology Inc.

DS21950E-page 17

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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
oscillator is a specialized structure with a low
temperature coefficient across the full range of
specified operation. See 

 for oscillator

frequencies.
The conversion time is an integer multiple of the
internal 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
simultaneous 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).