71m6543h-igtr/f Maxim Integrated Products, Inc., 71m6543h-igtr/f Datasheet - Page 55

• Manufacturer Part Number: 71m6543h-igtr/f
• Description: Energy Meter Ic
• Manufacturer: Maxim Integrated Products, Inc.

Unlike earlier generation Teridian SoCs, the 71M6543F/H does not use the ADC to read the
temperature sensor. Instead, it uses a technique that is operational in SLP and LCD mode, as well as
BRN and MSN modes. This means that the temperature sensor can be used to compensate for the
frequency variation of the crystal, even in SLP mode while the MPU is halted. See
Temperature Compensation
In MSN and BRN modes, the temperature sensor is awakened on command from the MPU by setting the
TEMP_START (I/O RAM 0x28B4[6]) control bit. In SLP and LCD modes, it is awakened at a regular rate
set by TEMP_PER[2:0] (I/O RAM 0x28A0[2:0]).
The result of the temperature measurement is read from the two I/O RAM locations STEMP[10:3] (I/O
RAM 0x2881) and STEMP[2:0] (I/O RAM 0x2882[7:5]). Note that both of these I/O RAM locations must be
read and properly combined to form the STEMP[10:0] 11-bit value (see STEMP in
11-bit value is in 2’s complement form and ranges from -1024 to +1023 (decimal).
The equations below are used to calculate the sensed temperature. The first equation applies when the
71M6543F is in MSN mode and TEMP_PWR = 1. The second equation applies when the 71M6543F is in
BRN mode, and in this case, the TEMP_PWR and TEMP_BSEL bits must both be set to the same value, so
that the battery that supplies the temperature sensor is also the battery that is measured and reported in
BSENSE. Thus, the second equation requires reading STEMP and BSENSE. In the second equation,
BSENSE (the sensed battery voltage) is used to obtain a more accurate temperature reading when the IC
is in BRN mode.
For the 71M6543F in MSN Mode (with TEMP_PWR = 1):
For the 71M6543F in BRN Mode, (with TEMP_PWR=TEMP_BSEL):
Table 46
v1.0
TBYTE_BUSY
TEMP_PER[2:0]
TEMP_BAT
Name
measurement may not finish. In this case, firmware may complete the measurement by selecting
V3P3D (TEMP_PWR = 1).
If TEMP_PWR selects VBAT_RTC when the battery is nearly discharged, the temperature
shows the I/O RAM registers used for temperature and battery measurement.
Temp
Table 46: I/O RAM Registers for Temperature and Battery Measurement
(
o
28A0[2:0]
Location
C
28A0[3]
28A0[4]
)
=
. 0
© 2008–2011 Teridian Semiconductor Corporation
325
on page 52.
⋅
Rst
STEMP
0
0
0
Temp
Wk
0
–
–
(
+
°
C
. 0
R/W
R/W
)
Dir
R
00208
=
. 0
325
Indicates that hardware is still writing the 0x28A0
byte. Additional writes to this byte are locked out
while it is one. Write duration could be as long as 6 ms.
Sets the period between temperature measurements.
Automatic measurements can be enabled in any
mode (MSN, BRN, LCD, or SLP).
Causes VBAT to be measured whenever a
temperature measurement is performed.
Description
TEMP_PER
⋅
⋅
STEMP
BSENSE
1-6
0
7
+
22
2
Time
Manual updates (see TEMP_START)
2 ^ (3+TEMP_PER) (seconds)
Continuous
−
. 0
584
⋅
BSENSE
71M6543F/H Data Sheet
Table
2.5.4.4 RTC
+
46). The resulting
62
9 .
55