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MAX17047
ModelGauge m3 Fuel Gauge
For easiest software compatibility between systems,
confiigure CGAIN to keep current LSB resolution at
0.15625mA. This preserves resolution of current readings
and capacities. Both these registers are signed two’s
complement. The default values of 4000h for CGAIN and
0000h for COFF preserve factory calibration and unit
values (1.5625FV). Figure 54 shows the CGAIN register
format and Figure 55 shows the COFF register format.
Temperature Measurement
While in active mode and Ten = 1 in the CONFIG register,
the device periodically measures the voltage between
the AIN and CSP pins and compares the result to the volt-
age of the THRM pin. The device stores the result, a ratio-
metric value from 0 to 100%. The resulting data is placed
in the AIN register every 1.4s with an LSB of 0.0122%.
Conversions are initiated by connecting the THRM and
VTT pins internally. This enables the active pullup to
the external voltage-divider network. After the pullup is
enabled, the device waits for a settling period of t
PRE
prior to making measurements on the AIN pin. When
ETHRM = 1, FTHRM = 0, the active pullup is disabled
when temperature measurements are complete. This fea-
ture limits the time the external resistor-divider network
is active and lowers the total amount of energy used by
the system.
When Tex = 0 and Ten = 1 in the CONFIG register, the
device converts the AIN register to a temperature using
the temperature gain (TGAIN) and temperature offset
(TOFF) register values:
Temperature Register = (AIN Register O
TGAIN Register/16384) + (TOFF Register O 2)
The resulting value is stored in the Temperature register
each time the AIN register is updated. Additionally, the
device maintains a record of the minimum and maximum
temperature measured by the device, and an average
temperature over a time period defined by the host.
Table 4 lists the recommended TGAIN and TOFF register
values for common NTC thermistors.
Table 4. Recommended TGAIN and TOFF Register Values for Common NTC
Thermistors
Figure 54. CGAIN Register Format (Input)
Figure 55. COFF Register Format (Input)
THERMISTOR
R
25C
(kI)
BETA RECOMMENDED TGAIN RECOMMENDED TOFF
Semitec
103AT-2
10 3435 E3E1h 290Eh
Fenwal
197-103LAG-A01
10 3974 E71Ch 251Ah
TDK
Type F
10 4550 E989h 22B1h
Figure 54
MSB—ADDRESS 2Eh LSB—ADDRESS 2Eh
S 2
0
2
-1
2
-2
2
-3
2
-4
2
-5
2
-6
2
-7
2
-8
2
-9
2
-10
2
-11
2
-12
2
-13
2
-14
MSb LSb MSb LSb
2
0
UNITS: 0.0061%
Figure 55
MSB—ADDRESS 2FH LSB—ADDRESS 2Fh
S 2
14
2
13
2
12
2
11
2
10
2
9
2
8
2
7
2
6
2
5
2
4
2
3
2
2
2
1
2
0
MSb LSb MSb LSb
UNITS: 3.125FV/R
SENSE
(34 Seiten)
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