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

6.25

Vh. 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 100

V 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:

6.25

Vh/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

ACR LSb

VSS -

VSNS

20m



15m



10m



5m



6.25

Vh

312.5

Ah

416.7

Ah

625

Ah

1.250mAh