DS2780 Standalone Fuel Gauge IC
10 of 31
current measurement and the conversion timebase. The ACR has a range of 0 to 409.6mVh with an LSb of
6.25Vh. Additional read-only registers (ACRL) hold fractional results of each accumulation to avoid truncation
errors. Accumulation of charge current above the maximum register value is reported at the maximum register
value (7FFFh); conversely, accumulation of discharge current below the minimum register value is reported at the
minimum value (8000h).
Charge currents (positive Current register values) less than 100V are not accumulated in order to mask the effect
of accumulating small positive offset errors over long periods. This limits the minimum charge current, for coulomb-
counting purposes, to 5mA for RSNS = 0.020 and 20mA for RSNS = 0.005.
Read and write access is allowed to the ACR. The ACR must be written MSByte first then LSByte. The write must
be completed within 3.515s (one ACR register update period). A write to the ACR forces the ADC to perform an
offset correction conversion and update the internal offset correction factor. Current measurement and
accumulation begins with the second conversion following a write to the ACR. Writing the ACR clears the fractional
values in the ACRL. The format of the ACR is shown in Figure 8, and the ACRL is shown in Figure 9.
To preserve the ACR value in case of power loss, it is backed up to EEPROM. The ACR value is recovered from
EEPROM on power-up. See the Memory Map in Table 2 for specific address location and backup frequency.
Figure 8. Accumulated Current Register Format, ACR
ACR
R/W & EE
MSB—Address 10h LSB—Address 11h
2
15
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: 6.25Vh/Rsns
Figure 9. Fractional/Low Accumulated Current Register Format, ACRL
ACRL
Read Only
MSB—Address 12h LSB—Address 13h
2
11
2
10
2
9
2
8
2
7
2
6
2
5
2
4
2
3
2
2
2
1
2
0
X X X X
MSb LSb MSb LSb
“X”: reserved Units:1.526nVHr/R
SNS
ACR LSb
R
SNS
VSS
-
VSNS
20m 15m 10m 5m
6.25Vh 312.5Ah 416.7Ah 625Ah
1.250mAh
