71M6521BE Datasheet, PDF (14/97 Pages) Teridian Semiconductor Corporation – Energy Meter IC

71M6521BE
Energy Meter IC
DATA SHEET
JANUARY 2008
On-chip hardware provides a maximum pulse width feature: PLS_MAXWIDTH[7:0] selects a maximum negative pulse width to
be ‘Nmax’ updates according to the formula: Nmax = (2*PLS_MAXWIDTH+1). If PLS_MAXWIDTH = 255, no width checking is
performed.
Given that PLS_INTERVAL = 81, the maximum pulse width is determined by:
Maximum Pulse Width = (2 * PLS_MAXWIDTH +1) * 81*4*203ns = 65.8µs + PLS_MAXWIDTH * 131.5µs
The CE pulse output polarity is programmable to be either positive or negative. Pulse polarity may be inverted with PLS_INV.
When this bit is set, the pulses are active high, rather than the more usual active low.
CE Functional Overview
The ADC processes one sample per channel per multiplexer cycle. Figure 4 shows the timing of the samples taken during one
multiplexer cycle.
The number of samples processed during one accumulation cycle is controlled by the I/O RAM registers PRE_SAMPS
(0x2001[7:6]) and SUM_CYCLES (0x2001[5:0]). The integration time for each energy output is
PRE_SAMPS * SUM_CYCLES / 2520.6, where 2520.6 is the sample rate [Hz]
For example, PRE_SAMPS = 42 and SUM_CYCLES = 50 will establish 2100 samples per accumulation cycle. PRE_SAMPS = 100
and SUM_CYCLES = 21 will result in the exact same accumulation cycle of 2100 samples or 833ms. After an accumulation
cycle is completed, the XFER_BUSY interrupt signals to the MPU that accumulated data are available.
IB
VB
IA
VA
1/32768Hz =
30.518µs
13/32768Hz = 397µs
per mux cycle
Figure 4: Samples from Multiplexer Cycle
The end of each multiplexer cycle is signaled to the MPU by the CE_BUSY interrupt. At the end of each multiplexer cycle,
status information, such as sag data and the digitized input signal, is available to the MPU.
Page: 14 of 97
© 2005-2008 TERIDIAN Semiconductor Corporation
V1.0