DS2746 Просмотр технического описания (PDF) - Maxim Integrated

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DS2746

Low-Cost 2-Wire Battery Monitor with Ratiometric A/D Inputs

Maxim Integrated 

DS2746 Low-Cost 2-Wire Battery Monitor

Table 1. Current Resolution for Various RSNS Values

VSS - VSNS

6.25μV

CURRENT RESOLUTION (1 LSB)

20mΩ

312.5µA

15mΩ

416.7µA

RSNS

10mΩ

625µA

5mΩ

1.25mA

Table 2. Current Range for Various RSNS Values

VSS - VSNS

±51.2mV

CURRENT INPUT RANGE

20mΩ

±2.56A

15mΩ

±3.41A

RSNS

10mΩ

±5.12A

5mΩ

±10.24A

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

approximately once per hour. The resulting correction factor is applied to the subsequent 1023 measurements.

During the offset correction conversion, the ADC does not measure the SNS to VSS 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 error due to offset correction is typically

much less than 1/1024 of the expected reading.

CURRENT ACCUMULATION

The Accumulated Current register (ACR) serves as an up/down counter holding a running count of charge stored in

the battery. Current measurement results, plus a programmable bias value are internally summed, or accumulated,

at the completion of each current measurement conversion period with the results displayed in the ACR. The ACR

has a range of 0mVh to +409.6mVh with an LSb of 6.25μVh. Additional registers hold fractional results of each

accumulation, however, these bits are not user accessible. The ACR count clamps at FFFFh when accumulating

charge values and at 0000h when accumulating discharge values.

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

cleared. A write to the ACR also forces the ADC to measure its offset and update the offset correction factor.

Current measurement and accumulation resume (using the new offset correction) with the second conversion

following the write to the ACR. Figure 9 describes the ACR address, format, and resolution. Table 3 shows the

ACR’s dynamic range for several different sense resistor options.

Figure 9. Accumulated Current Register Format

MSB—Address 10h

LSB—Address 11h

215 214 213 212 211 210 29 28

MSb

LSb

“S”: sign bit

27 26 25 24 23 22 21 20

MSb

LSb

Units: 6.25μVh/Rsns

10 of 16

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