6 71m654x battery monitor, 71m654x battery monitor – Rainbow Electronics 71M6542G User Manual
Page 57
v1.1
© 2008–2011 Teridian Semiconductor Corporation
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Name
Location
Rst
Wk Dir Description
TEMP_BAT
28A0[4]
0
–
R/W
Causes VBAT to be measured whenever a
temperature measurement is performed.
TEMP_START
28B4[6]
0
–
R/W
TEMP_PER[2:0] must be zero in order for TEMP_START
to function. If TEMP_PER[2:0] = 0, then setting
TEMP_START starts a temperature measurement.
Ignored in SLP and LCD modes. Hardware clears
TEMP_START when the temperature measurement is
complete. The MPU must wait for TEMP_START to
clear before reading STEMP[10:0] and before setting
TEMP_START again.
TEMP_PWR
28A0[6]
0
–
R/W
Selects the power source for the temperature sensor:
1 = V3P3D, 0 = VBAT_RTC. This bit is ignored in
SLP and LCD modes, where the temperature sensor is
always powered by VBAT_RTC.
TEMP_BSEL
28A0[7]
0
–
R/W
Selects which battery is monitored by the
temperature sensor: 1 = VBAT, 0 = VBAT_RTC
TEMP_TEST[1:0]
2500[1:0]
0
–
R/W
Test bits for the temperature monitor VCO.
TEMP_TEST must be 00 in regular operation. Any
other value causes the VCO to run continuously with
the control voltage described below.
TEMP_TEST Function
00
Normal operation
01
Reserved for factory test
1X
Reserved for factory test
STEMP[10:3]
STEMP[2:0]
2881[7:0]
2882[7:5]
R
R
The result of the temperature measurement.
To correctly form STEMP[10:0], the MPU must read
0x2881[7:0], shift it left by three bit positions (padding
LSBs with zeros), then read 0x2882[7:5], shift it right
by 5-bits (padding the 5 MSBs with zeros), and then
logically OR the two quantities together.
BSENSE[7:0]
2885[7:0]
–
–
R
The result of the battery measurement.
BCURR
2704[3]
0
0
R/W
Connects a 100 µA load to the battery selected by
TEMP_BSEL.
Refer to the 71M6xxx Data Sheet for information on reading the temperature sensor in the 71M6x01
devices.
2.5.6 71M654x Battery Monitor
The 71M654x temperature measurement circuit can also monitor the batteries at the VBAT and
VBAT_RTC pins. The battery to be tested (i.e., VBAT or VBAT_RTC pin) is selected by TEMP_BSEL (I/O
RAM 0x28A0[7]).
When TEMP_BAT (I/O RAM 0x28A0[4]) is set, a battery measurement is performed as part of each
temperature measurement. The value of the battery reading is stored in register BSENSE[7:0] (I/O RAM
0x2885). The following equation is used to calculate the voltage measured on the VBAT pin (or VBAT_RTC
pin) from the BSENSE[7:0] and STEMP[10:0] values. The result of the equation below is in volts.
V
STEMP
V
BSENSE
V
RTC
orVBAT
VBAT
000276
.
0
]
0
:
10
[
0246
.
0
)
142
]
0
:
7
[
(
293
.
3
)
_
(
⋅
+
⋅
−
+
=
In MSN mode, a 100 µA de-passivation load can be applied to the selected battery (i.e., selected by the
TEMP_BSEL bit) by setting the BCURR (I/O RAM 0x2704[3]) bit. Battery impedance can be measured by
taking a battery measurement with and without BCURR. Regardless of the BCURR bit setting, the battery
load is never applied in BRN, LCD, and SLP modes.