DS2740 データシートの表示（PDF） - Maxim Integrated

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DS2740

High-Precision Coulomb Counter

Maxim Integrated 

DS2740

PART

DS2740U

DS2740BU

CONVERSION

TIME

3.515s

0.878s

CURRENT RESOLUTION (1 LSB)

VIS1 - VIS2 20mΩ

RSNS

15mΩ 10mΩ

5mΩ

1.5625μV 78.13μA 104.2μA 156.3μA 312.5μA

6.250μV 312.5μA 416.7μA 625μA 1.250mA

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

correction occurs approximately once per hour in the DS2740U and four times per hour in the

DS2740BU. 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 a 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 10h

LSB—Address 11h

S 214 213 212 211 210 29 28

MSb

LSb

27 26 25 24 23 22 21 20

MSb

LSb

Units: 6.25μVh/RSNS

PART

UPDATE

INTERVAL VIS1 - VIS2

DS2740U

3.515s

DS2740BU 0.878s

6.25μVh

20mΩ

312.5μAh

ACR LSB

RSNS

15mΩ 10mΩ

416.7μAh 625μAh

5mΩ

1.250mAh

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