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Current measurement, Current register (0ah), Figure 50. maxminv register format (outp – Rainbow Electronics MAX17047 User Manual

Page 36: Figure 51. current register format (outp, Table 3. sample current register convers, Table 3. sample current register conversions

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MAX17047

ModelGauge m3 Fuel Gauge

values. If V

CELL

is larger than the maximum or less than

the minimum, the corresponding value is replaced with
the new reading. At power-up, the MaxV

CELL

value is set

to 00h (the minimum) and the MinV

CELL

value is set to

FFh (the maximum). Therefore, both values are changed
to the V

CELL

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.

Figure 50

shows the MaxMinV

CELL

register format.

Current Measurement

While in active mode, the device periodically measures
the voltage between the CSN and CSP pins over a
Q

51.2mV range. The resulting data is stored as a signed

two’s-complement value in the Current register every
175.8ms with an LSb value of 1.5625FV/R

SENSE

. All

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.

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
of 1.5625FV/R

SENSE

. Voltages outside the minimum and

maximum register values are reported as the minimum or
maximum value.

Figure 51

shows the Current register format

and

Table 3

shows the Sample Current register conversions.

Figure 51. Current Register Format (Output)

Figure 50. MaxMinV

CELL

Register Format (Output)

Table 3. Sample Current Register Conversions

FUNCTION

SENSE

RESISTOR (I)

CGAIN

REGISTER

CURRENT REGISTER

RESOLUTION (µA)

CURRENT REGISTER

RANGE (A)

MAXIMUM CELL

CAPACITY (Ah)

Adjusting sense

resistor to meet

range and accuracy

requirements

0.005

4000h

312.50

Q

10.24

32.768

0.010

4000h

156.25

Q

5.12

16.384

0.020

4000h

78.125

Q

2.56

8.192

Adjusting CGAIN to
keep units constant

0.005

8000h

156.25

Q

5.12

16.384

0.010

4000h

156.25

Q

5.12

16.384

0.020

2000h

156.25

Q

5.12

16.384

Figure 51

MSB—ADDRESS 0Ah

LSB—ADDRESS 0Ah

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: 1.5625FV/R

SENSE

Figure 50

MSB—ADDRESS 1Bh

LSB—ADDRESS 1Bh

MAX

7

MAX

6

MAX

5

MAX

4

MAX

3

MAX

2

MAX

1

MAX

0

MIN

7

MIN

6

MIN

5

MIN

4

MIN

3

MIN

2

MIN

1

MIN

0

MSb

LSb

MSb

LSb

UNITS: 20mV