MCP3550 Microchip Technology, MCP3550 Datasheet - Page 14

• Manufacturer Part Number: MCP3550
• Description: Low-Power, Single-Channel 22-Bit Delta-Sigma ADCs
• Manufacturer: Microchip Technology

MCP3550/1/3
:
FIGURE 4-2:
MCP3550-50 Device.
:
FIGURE 4-3:
MCP3550-60 Device.
:
FIGURE 4-4:
MCP3551 Device, Simultaneous 50/60 Hz
Rejection.
DS21950D-page 14
-100
-120
-100
-120
-100
-110
-120
-20
-40
-60
-80
-20
-40
-60
-80
-10
-20
-30
-40
-50
-60
-70
-80
-90
0
0
0
0
0
0
10 20 30 40 50 60 70 80 90 100 110
50
60
SINC Filter Response,
SINC Filter Response,
SINC Filter Response,
Frequency (Hz)
Frequency (Hz)
Frequency (Hz)
100
120
150
180
200
240
FIGURE 4-5:
Integer Multiples of the Sampling Frequency (f
4.3
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).
-100
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-140
-20
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-80
0
0
Internal Oscillator
28160
56320
84480 112640 140800 168960 197120 225280 253440
SINC Filter Response at
© 2007 Microchip Technology Inc.
Frequency (Hz)
s
).