MAX17047/MAX17050
ModelGauge m3 Fuel Gauge
devices are calibrated for current-measurement accu-
racy at the factory. However, if the application requires,
Current Register readings can be adjusted by changing
the COFF and CGAIN register settings.
Additionally, the device maintains a record of the mini-
mum and maximum current measured by the device,
and an average current over a time period defined by
the host. Contents of the Current and AverageCurrent
registers are 0000h until the first conversion cycle time
period after IC power-up. The last values of the Current
and AverageCurrent registers are maintained when the
IC enters shutdown mode.
MaxMinV
Register (1Bh)
CELL
The MaxMinV
register maintains the maximum and
CELL
minimum V
register values since the last fuel-gauge
reset or until reset by the host software. Each time the
register updates, it is compared against these
is larger than the maximum or less than
the minimum, the corresponding value is replaced with
the new reading. At power-up, the MaxV
to 00h (the minimum) and the MinV
FFh (the maximum). Therefore, both values are changed
to the V register reading after the first update. Host
software can reset this register by writing it to its power-
up value of 00FFh. The maximum and minimum voltages
are each stored as 8-bit values with a 20mV resolution.
CELL
V
CELL
values. If V
CELL
value is set
value is set to
CELL
CELL
CELL
Current Register (0Ah)
While in active mode, the device periodically measures the
voltage between the CSN and CSP pins over a Q51.2mV
range. The resulting data is stored as a two’s-complement
value in the Current register every 175.8ms with an LSb value
Figure 51 shows the MaxMinV
register format.
CELL
Current Measurement
While in active mode, the device periodically measures
the voltage between the CSN and CSP pins over a
Q51.2mV range. The resulting data is stored as a signed
two’s-complement value in the Current register every
of 1.5625FV/R
. Voltages outside the minimum and
SENSE
maximum register values are reported as the minimum or
maximum value. Figure 52 shows the Current register format
and Table 3 shows the Sample Current register conversions.
175.8ms with an LSb value of 1.5625FV/R
. All
SENSE
MSB—ADDRESS 1Bh
LSB—ADDRESS 1Bh
7
6
5
4
3
2
1
0
7
6
5
4
3
2
1
0
MAX MAX MAX MAX MAX MAX MAX MAX
MIN MIN MIN MIN MIN MIN MIN MIN
MSb
LSb
MSb
LSb
UNITS: 20mV
Figure 51. MaxMinV
Register Format (Output)
CELL
Table 3. Sample Current Register Conversions
SENSE
RESISTOR (I)
CGAIN
REGISTER
CURRENT REGISTER
RESOLUTION (µA)
CURRENT REGISTER MAXIMUM CELL
FUNCTION
RANGE (A)
Q10.24
Q5.12
CAPACITY (Ah)
0.005
0.010
0.020
4000h
4000h
4000h
312.50
156.25
78.125
32.768
Adjusting sense
resistor to meet
range and accuracy
requirements
16.384
Q2.56
8.192
0.005
0.010
0.020
7FFFh
4000h
2000h
156.25
156.25
156.25
Q5.12
Q5.12
Q5.12
16.384
16.384
16.384
Adjusting CGAIN to
keep units constant
���������������������������������������������������������������� Maxim Integrated Products 37
MAXIM [ MAXIM INTEGRATED PRODUCTS ]
