DS2746G+TR MAXIM [Maxim Integrated Products], DS2746G+TR Datasheet - Page 9

• Manufacturer Part Number: DS2746G+TR
• Description: Low-Cost 2-Wire Battery Monitor with Ratiometric A/D Inputs
• Manufacturer: MAXIM [Maxim Integrated Products]

AUXILARY INPUT MEASUREMENTS
The DS2746 allows for measuring two auxiliary measurement inputs, AIN0 and AIN1, with respect to V
inputs are designed for measuring resistor ratios, particularly useful for measuring thermistor or pack identification
resistors. At a time of t
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 V
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 (>15M) to be connected to a wide range of voltage divider
resistances.
Figure 7. Auxiliary Input Registers Format
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, R
pins. The voltage sense range between SNS and V
V
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
SNS
is less than V
AIN0
MSb
“S”: sign bit, “X”: reserved
AIN1
MSb
“S”: sign bit, “X”: reserved
MSb
“S”: sign bit
S
S
S
2
2
2
10
10
12
SS
, and negative current values occur when V
2
MSB—Address 0Ah
MSB—Address 0Eh
MSB—Address 08h
2
2
PRE
11
9
9
prior to the beginning of a measurement cycle on AIN0 or AIN1, the V
2
2
2
10
8
8
2
2
2
7
7
9
2
2
2
6
6
8
2
2
2
5
5
7
2
2
2
LSb
LSb
LSb
4
4
6
SS
9 of 17
is ±51.2mV. Note that positive current values occur when
MSb
MSb
MSb
2
2
2
3
3
5
SNS
2
2
2
is greater than V
2
2
4
SNS
2
LSB—Address 0Bh
2
2
LSB—Address 09h
LSB—Address 0Fh
1
1
3
, connected between the SNS and V
OUT
Units: 1LSB = V
Units: 1LSB = V
2
2
2
removes reference tolerance from
0
0
2
Units: 2
SS
2
X
X
1
. Peak signal amplitudes up
0
2
= 6.25V/Rsns
X
X
0
VOUT
VOUT
X
X
X
OUT
* 1/2047
* 1/2047
pin puts out a
LSb
LSb
LSb
X
X
X
SS
. These
SS