71M6521DE Datasheet, PDF (13/107 Pages) Teridian Semiconductor Corporation – Energy Meter IC

71M6521DE/DH/FE Data Sheet
Battery Monitor
The battery voltage is measured by the ADC during alternative multiplexer frames if the BME (Battery Measure
Enable) bit in the I/O RAM is set. While BME is set, an on-chip 45kΩ load resistor is applied to the battery, and a
scaled fraction of the battery voltage is applied to the ADC input. After each alternative MUX frame, the result of the
ADC conversion is available at CE DRAM address 07. BME is ignored and assumed zero when system power is not
available (V1 < VBIAS). See the Battery Monitor section of the Electrical Specifications for details regarding the ADC
LSB size and the conversion accuracy.
Functional Description
The AFE functions as a data acquisition system, controlled by the MPU. The main signals (IA, VA, IB, VB) are
sampled and the ADC counts obtained are stored in CE DRAM where they can be accessed by the CE and, if
necessary, by the MPU. Alternate multiplexer cycles are initiated less frequently by the MPU to gather access to the
slow temperature and battery signals.
VREF
IA
VA
IB
MUX
VB
VBAT
VBIAS
TEMP
MUX
MUX
CTRL
EQU
MUX_ALT
CHOP_E
MUX_DIV
VREF
VREF_CAL
VREF_DIS
CROSS
CK32
VBIAS
∆Σ ADC
CONVERTER
V3P3A
-
+
ADC_E
VREF
FIR_DONE
FIR_START
4.9MHz
FIR
FIR_LEN
Figure 3: AFE Block Diagram
Digital Computation Engine (CE)
The CE, a dedicated 32-bit signal processor, performs the precision computations necessary to accurately measure
energy. The CE calculations and processes include:
• Multiplication of each current sample with its associated voltage sample to obtain the energy per sample
(when multiplied with the constant sample time).
• Frequency-insensitive delay cancellation on all six channels (to compensate for the delay between samples
caused by the multiplexing scheme).
• 90° phase shifter (for VAR calculations).
• Pulse generation.
• Monitoring of the input signal frequency (for frequency and phase information).
• Monitoring of the input signal amplitude (for sag detection).
• Scaling of the processed samples based on calibration coefficients.
The CE program resides in flash memory. Common access to flash memory by CE and MPU is controlled by a
memory share circuit. Each CE instruction word is two bytes long. Allocated flash space for the CE program cannot
exceed 1024 words (2KB). The CE program counter begins a pass through the CE code each time multiplexer state 0
begins. The code pass ends when a HALT instruction is executed. For proper operation, the code pass must be
completed before the multiplexer cycle ends (see System Timing Summary in the Functional Description Section).
The CE program must begin on a 1Kbyte boundary of the flash address. The I/O RAM register CE_LCTN[4:0]
defines which 1KB boundary contains the CE code. Thus, the first CE instruction is located at 1024*CE_LCTN[4:0].
The CE DRAM can be accessed by the FIR filter block, the RTM circuit, the CE, and the MPU. Assigned time slots
are reserved for FIR, RTM, and MPU, respectively, to prevent bus contention for CE DRAM data access. Holding re-
gisters are used to convert 8-bit wide MPU data to/from 32-bit wide CE DRAM data, and wait states are inserted as
needed, depending on the frequency of CKMPU.
Rev 2
Page: 13 of 107