71M6511 Maxim, 71M6511 Datasheet - Page 9

• Manufacturer Part Number: 71M6511
• Description: The 71M6511 and 71M6511H are highly integrated SoCs with an MPU core, RTC, flash, and LCD driver
• Manufacturer: Maxim

The MUX_ALT bit requests an alternate multiplexer cycle. The bit may be asserted on any MPU cycle and may be sub-
sequently de-asserted on any cycle including the next one. A rising edge on MUX_ALT will cause the Control Circuit to wait
until the next multiplexer cycle and implement a single alternate cycle.
Multiplexer Control Circuit also controls the FIR filter initiation and the chopping of the ADC reference voltage, VREF. The
Multiplexer Control Circuit is clocked by CK32, the 32768Hz clock from the PLL block, and launches each pass through the CE
program.
Table 2 shows the possible settings for MUX_DIV and FIR_LEN and the resulting channels sampled along with sample
frequencies.
ADC
A single 21/22-bit delta-sigma A/D converter (ADC) digitizes the power inputs to the AFE. The resolution of the ADC is
programmable using the I/O RAM register FIR_LEN register (0x2005[4]). ADC resolution may be selected to be 21 bits
(FIR_LEN=0), or 22 bits (FIR_LEN=1). Conversion time is two cycles of CK32 with FIR_LEN = 0 and three cycles with FIR_LEN
= 1.
In order to provide the maximum resolution, the ADC should be operated with FIR_LEN = 1. Accuracy, timing and
functional specifications in this data sheet are based on FIR_LEN = 1 and MUX_DIV = 1 (four CK32 cycles). Alternative
specifications are also provided for FIR_LEN = 1 and MUX_DIV = 2 (three CK32 cycles) in the CE Program and
Environment section.
Initiation of each ADC conversion is controlled by the Multiplexer Control Circuit as described previously.
FIR Filter
The finite impulse response (FIR) filter is an integral part of the ADC and it is optimized for use with the multiplexer. The
purpose of the FIR is to decimate the ADC output to the desired resolution. At the end of each ADC conversion, the output
data of the FIR filter (raw data) is stored into the CE DRAM location determined by the multiplexer selection. The location of
the raw data in the CE DRAM is specified in the CE Program and Environment Section.
Voltage Reference
The 71M6511/6511H includes an on-chip precision bandgap voltage reference that incorporates auto-zero techniques. The
reference of the 71M6511H is trimmed in production to minimize errors caused by component mismatch and drift. The result is
a voltage output with a predictable temperature coefficient.
The voltage reference is chopper stabilized, i.e. the polarity can be switched by the MPU using the I/O RAM register
CHOP_ENA (0x2002[5:4]). The two bits in the CHOP_ENA register enable the MPU to operate the chopper circuit in regular or
inverted operation, or in “toggling” mode. When the chopper circuit is toggled in between multiplexer cycles, DC offsets on the
measured signals will automatically be averaged out.
The general topology of a chopped amplifier is given in Figure 2.
Page: 9 of 98
(0x2002[7.6])
MUX_DIV
A Maxim Integrated Products Brand
00
01
10
11
(mux states
Number of
per cycle)
channels
selected
Table 2: Channel control based on MUX_DIV and FIR_LEN
for code pass
---
CK32 states
4
3
2
© 2005–2010 Teridian Semiconductor Corporation
Number of
FIR_LEN = 0
9
7
5
frequency
Effective
sample
[Hz]
Single-Phase Energy Meter IC
4681.143
3640.89
6553.6
CK32 states
Number of
for code
Not Allowed
71M6511/71M6511H
pass
FIR_LEN =1
DATA SHEET
13
10
frequency
7
Effective
sample
[Hz]
2520.615
4681.143
3276.8
NOVEMBER 2010
V2.7