DS2746G Просмотр технического описания (PDF) - Maxim Integrated
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DS2746G Datasheet PDF : 16 Pages
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DS2746 Low-Cost 2-Wire Battery Monitor
AUXILARY INPUT MEASUREMENTS
The DS2746 allows for measuring two auxiliary measurement inputs, AIN0 and AIN1, with respect to VSS. These
inputs are designed for measuring resistor ratios, particularly useful for measuring thermistor or pack identification
resistors. At a time of tPRE prior to the beginning of a measurement cycle on AIN0 or AIN1, the VOUT pin puts out a
reference voltage in order to drive a resistive divider formed by a known resistor value, and the unknown resistance
to be measured. Making these measurements ratiometric with respect to VOUT removes reference tolerance from
the error calculations. Each auxiliary input measurement is updated every 660ms with the average voltage over the
220ms conversion period and placed in the AIN0 and AIN1 Registers in two’s complement form. The input
impedances of AIN0 and AIN1 are sufficiently large (>15MΩ) to be connected to a wide range of voltage divider
resistances.
Figure 7. Auxiliary Input Registers Format
AIN0
MSB—Address 08h
S 210 29 28 27 26 25 24
MSb
LSb
“S”: sign bit, “X”: reserved
LSB—Address 09h
23 22 21 20 X X X X
MSb
LSb
Units: 1LSB = VVOUT * 1/2047
AIN1
MSB—Address 0Ah
S 210 29 28 27 26 25 24
MSb
LSb
“S”: sign bit, “X”: reserved
LSB—Address 0Bh
23 22 21 20 X X X X
MSb
LSb
Units: 1LSB = VVOUT * 1/2047
CURRENT MEASUREMENT
In the active mode of operation, the DS2746 continually measures the current flow into and out of the battery by
measuring the voltage drop across a low-value current-sense resistor, RSNS, connected between the SNS and VSS
pins. The voltage sense range between SNS and VSS is ±51.2mV. Note that positive current values occur when
VSNS is less than VSS, and negative current values occur when VSNS is greater than VSS. Peak signal amplitudes up
to 102mV are allowed at the input as long as the continuous or average signal level does not exceed ±51.2mV over
the conversion period. The ADC samples the input differentially and updates the current register at the completion
of each conversion. The result is updated every 878ms with the average voltage and placed in the CURRENT
register in two’s compliment form. The current measurement register format is shown in Figure 8 and specifications
for several different sense resistor options are shown in Tables 1 and 2. Charge currents above the maximum
register value are reported at the maximum value (7FFFh = +51.2mV). Discharge currents below the minimum
register value are reported at the minimum value (8000h = -51.2mV).
Figure 8. Current Register Formats
MSB—Address 0Eh
S 212 211 210 29 28 27 26
MSb
LSb
“S”: sign bit
LSB—Address 0Fh
25 24 23 22 21 20 X X
MSb
LSb
Units: 20 = 6.25μV/Rsns
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