MCP3901A0-I/SS Microchip Technology, MCP3901A0-I/SS Datasheet - Page 11

• Manufacturer Part Number: MCP3901A0-I/SS
• Description: IC AFE 24BIT 64KSPS 20-SSOP
• Manufacturer: Microchip Technology

Specifications of MCP3901A0-I/SS

• Number Of Bits: 24
• Number Of Channels: 2
• Power (watts): 10mW
• Voltage - Supply, Analog: 4.5 V ~ 5.5 V
• Voltage - Supply, Digital: 2.7 V ~ 5.5 V
• Package / Case: 20-SSOP
• Ic Function: Analog Front End Device IC
• Supply Voltage Range: 4.5V To 5.5V
• Operating Temperature Range: -40°C To +85°C
• Digital Ic Case Style: SSOP
• No. Of Pins: 20
• Supply Voltage Max: 5.5V
• Output Voltage: 0.4 V
• Output Power: 14 mW
• Input Voltage: 4.5 V to 5.5 V, 2.7 V to 5.5 V
• Switching Frequency: 4 MHz
• Mounting Style: SMD/SMT
• Number Of Outputs: 2
• No. Of Channels: 2
• Rohs Compliant: Yes
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant, Lead free / RoHS Compliant
• Other names: MCP3901AO-I/SS; MCP3901AO-I/SS

2.1
FIGURE 2-1:
 2010 Microchip Technology Inc.
Voltage Sample
Current Sample
POWER MONITOR FIRMWARE DESCRIPTION
Chapter 2. Installation and Operation
2.1.1
Using the external ADC, the current and voltage samples must be acquired before the
correct values of the desired parameters can be computed. The MCU reads the values
of the samples from the ADC through the SPI bus.
The sampling speed of the ADC is controlled by the clock frequency of the MCP3901.
The MCU uses the Output Compare 1 module to generate a 50% pulse-width
modulation (PWM) signal that has a frequency of 901.120 kHz. This frequency can be
easily changed by modifying values in the Timer2 Period Register (PR2) and the
Compare Register 1 (CCPR1).
The sampling speed of the ADC is 1024 times lower than the master clock in the
MCP3901, meaning 880 sps at an Over Sampling Rate (OSR) of 256.
2.1.2
In order to obtain the desired parameter values out of the acquired samples, a signal
processing technique must be assumed. Since this design uses an 8-bit MCU, the
signal processing technique that is implemented must be fast enough to avoid limiting
the sampling speed, so that a time-domain analysis can be performed. The signal
processing technique is graphically described in Figure 2-1.
Block Diagram of the Signal Processing Algorithm.
Initially, the acquired samples go through a first-order Infinite Impulse Response
high-pass filter (IIR HPF), which has the following roles:
1. Removes the offset of the ADC
2. Compensates for the Sinc filters transfer function
HPF
HPF
LPF
LPF
RMS Voltage Scaling Factor
RMS Current Scaling Factor
Samples Acquisition
Signal Processing
Active Power Scaling Factor
LPF
LPF
LPF
MONITOR REFERENCE DESIGN
SQRT
SQRT
MCP3901 LOW-COST POWER
LPF
U
I
Active Power
Apparent Power
RMS
RMS
DS51915A-page 11
Power Factor