MAX17201 Datasheet, PDF (74/115 Pages) Maxim Integrated Products – Stand-Alone ModelGauge m5 Fuel Gauge

MAX17201/MAX17205/
MAX17211/MAX17215
Stand-Alone ModelGauge m5 Fuel Gauge
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Copper Trace Current Sensing
The MAX1720x/1x has the ability to measure current
using a copper board trace instead of a traditional sense
resistor. The main difference being the ability to adjust
to the change in sense resistance over temperature.
To enable copper trace current sensing, set the follow-
ing configuration bits: nNVCfg1.enCrv=0 and nNVCfg2.
enMet=1. The IC's default temperature adjustment is
0.4% per °C, but can be adjusted using the nTCurve reg-
ister if nNVCfg1.enMtl=1. Note that copper trace current
sensing cannot be enabled at the same time as thermistor
curve adjustment. For 1-ounce copper, a length to width
ratio of 6:1 will create a 0.0035Ω sense resistor which is
suitable for most applications. Table 13 summarizes the
IC setting for copper trace sensing.
Temperature Measurement
The IC can be configured to measure its own internal die
temperature and up to two external NTC thermistors. In
addition the IC can be configured to use any single input
or an average of both thermistors as the temperature
input to the fuel gauge calculations. See the nPackCfg
register for details.
Thermistor conversions are initiated by connecting the
THRM and REG3 pins internally. This enables the active
pullup to the external voltage-divider network. After the
pullup is enabled, the IC waits for a settling period of t_PRE
prior to making measurements on the AIN1 or AIN2 pins.
Measurement results are compared to the voltage of the
THRM pin and converted to a ratiometric value from 0 to
100%. The active pullup is disabled when temperature
measurements are complete. This feature limits the time
the external resistor-divider network is active and lowers
the total amount of energy used by the system.
The ratiometric results are converted to temperature
using the temperature gain (TGain), temperature offset
(TOff), and temperature curve (nTCurve) register values
each time the AIN1 and AIN2 pins are measured. Internal
die temperature measurements are factory calibrated and
are not affected by TGain, TOff, nTCurve register settings.
Additionally the IC maintains a record of the minimum and
maximum temperature measured, and an average tem-
perature over a time period defined by the host.
Temperature Measurement Timing
Temperature measurement channels are individually
enabled using the nPackCfg register. ADC measurement
order and firmware post processing determine when a
valid reading will become available to the user. In addi-
tion, not all channels are measured each time through the
firmware task loop. Selection options for enabled chan-
nels creates a large number of possible timing options.
Table 14 shows the timing for all temperature measure-
ments made by the IC for some typical pack configura-
tions. All times in this table are considered typical.
Table 13. Copper Trace Sensing
PARAMETER
nNVCfg1.enCRV
nNVCfg1.enMet
nNVCfg2.enMlt
nRense
R_SENSE Size
SETTING
0
1
0
0x012C
6:1
RESULT
Thermistor curve compensation disabled
Sense resistor temperature compensation
enabled
Sense resistor temperature compensa-
tion set to default of 0.4% per °C (typical
copper).
Sense resistor indicator to host software
set to 0.0035Ω as demonstrated on the
evaluation kit hardware.
A 6:1 length to width ratio of 1oz copper
gives a resistance of 0.0035Ω.
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