DS2740

5 of 15

CURRENT RESOLUTION (1 LSB)

PART

CONVERSION

TIME

20m

W

15m

W

10m

W

5m

W

DS2740

3.515s

1.5625

mV 78.13mA 104.2mA

156.3

mA

312.5

mA

DS2740B

0.878s

6.250

mV

312.5

mA 416.7mA

625

mA

1.250mA

Every 1024th conversion, the ADC measures its input offset to facilitate offset correction. Offset

correction occurs approximately once per hour in the DS2740 and four times per hour in the DS2740B.

The resulting correction factor is applied to the subsequent 1023 measurements. During the offset

correction conversion, the ADC does not measure the IS1 to IS2 signal. A maximum error of 1/1024 in

the accumulated current register (ACR) is possible, however, to reduce the error, the current measurement

just prior to the offset conversion is displayed in the current register and is substituted for the dropped

current measurement in the current accumulation process. The typical error due to offset correction is

much less than 1/1024.

CURRENT ACCUMULATOR

Current measurements are internally summed, or accumulated, at the completion of each conversion

period with the results displayed in the ACR. The accuracy of the ACR is dependent on both the current

measurement and the conversion timebase. The ACR has a range of ±204.8mVh with an LSb of

6.25µVh

. Additional registers hold fractional results of each accumulation, however, these bits are not

user accessible.

Read and write access is allowed to the ACR. Whenever the ACR is written, fractional accumulation

results are cleared. Also, a write forces the ADC to measure its offset and update the offset correction

factor. The current measurement and accumulation begin with the second conversion following a write to

the ACR. Figure 4 describes the ACR address, format, and resolution.

Figure 4. CURRENT ACCUMULATOR FORMAT

MSB—Address 10

LSB—Address 11

MSb

LSb

MSb

LSb

Units: 6.25

mVh/Rsns

ACR LSB

PART

UPDATE

INTERVAL

20m

W

15m

W

10m

W

5m

W

DS2740

3.515s

DS2740B

0.878s

6.25

mVh

312.5

mAh

416.7

mAh

625

mAh

1.250mAh