71M6533 Datasheet, PDF (13/132 Pages) Teridian Semiconductor Corporation – Energy Meter IC

FDS_6533_6534_004
71M6533/G/H and 71M6534/H Data Sheet
CHOP_E[1:0] has four states: positive, reverse, and two toggle states. In the positive state, CHOP_E[1:0]
= 01, CROSS and CHOP_CLK are held low. In the reverse state, CHOP_E[1:0] = 10, CROSS and
CHOP_CLK are held high. In the first toggle state, CHOP_E [1:0] = 00, CROSS is automatically toggled
near the end of each multiplexer frame and an ALT frame is forced during the last multiplexer frame in each
SUM cycle. It is desirable that CROSS take on alternate values during each ALT frame. For this reason,
if CHOP_E[1:0] = 00, CROSS will not toggle at the end of the multiplexer frame immediately preceding the
ALT frame in each accumulation interval.
Accumulation interval n
Accumulation interval n+1
123 4
Multiplexer frames ^{2519 2520 1 2 3 4} Multiplexer frames ^{2519 2520}
Alternative MUX cycle
Alternative MUX cycle
CROSS
CROSS
Figure 3: CROSS Signal with CHOP_E[1:0] = 00
Figure 3 shows CROSS over two accumulation intervals when CHOP_E[1:0] = 00. At the end of the
first interval, CROSS is low, at the end of the second interval, CROSS is high. The offset error for
the two temperature measurements taken during the ALT multiplexer frames will be averaged to zero.
Note that the number of multiplexer frames in an accumulation interval is always even. Operation
with CHOP_E[1:0] = 00 does not require control of the chopping mechanism by the MPU while eliminating
the offset for temperature measurement.
In the second toggle state, CHOP_E[1:0] = 11, no ALT frame is forced during the last multiplexer cycle in
an accumulation interval, and CROSS always toggles near the end of each multiplexer frame.
The internal bias voltage, VBIAS (typically 1.6 V), is used by the ADC as a reference when measuring the
temperature and battery monitor signals.
1.2.6 Temperature Sensor
The 71M6533 and 71M6534 include an on-chip temperature sensor implemented as a bandgap reference.
It is used to determine the die temperature. The MPU may request an alternate multiplexer cycle containing
the temperature sensor output by asserting MUX_ALT.
The primary use of the temperature data is to determine the magnitude of compensation required to offset
the thermal drift in the system (see Section 3.5 Temperature Compensation).
1.2.7 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 45 kΩ 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 XRAM address 0x0B. BME is ignored and
assumed zero when system power is not available (V1 < VBIAS). See Section 6.4.5 for details regarding
the ADC LSB size and the conversion accuracy.
1.2.8 AFE Functional Description
The AFE functions as a data acquisition system, controlled by the MPU. The main signals (IA, VA, IB,
VB, etc.) are sampled and the ADC counts obtained are stored in XRAM 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.
Figure 4 shows the block diagram of the AFE.
Rev 2
13