DS2790 Maxim Integrated Products, DS2790 Datasheet - Page 30

• Manufacturer Part Number: DS2790
• Description: Programmable 1-Cell Li-Ion Fuel Gauge and Protector
• Manufacturer: Maxim Integrated Products

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ANALOG-TO-DIGITAL CONVERSION
The DS2790 performs real-time measurements of system temperature, voltage, current, and accumulated current.
The DS2790’s analog-to-digital converter is controlled by an internal state machine that sequences the
measurements, and stores the results in memory. The conversion results of the ADC are mapped into data
memory starting at word address 6003h, as shown in table 12. Programs should read a measurement value as a
word to ensure that the value does not change between instructions.
The DS2790 current measurement system is designed to provide timely data on charge and discharge current at a
moderate resolution level while simultaneously accumulating high resolution average data to support accurate
coulomb counting. Current is measured by sampling the voltage drop across a series sense resistor, R
connected between SNS1 and SNS2. Individual current samples are taken every 1/f
averaged to report Current, Average Current, and Accumulated Current values.
The DS2790 measures voltage as a difference between the V
samples are taken approximately every 1/f
Voltage register.
The DS2790 measures temperature directly on chip. Individual temperature samples are taken every 10/f
(6.87ms). Multiple samples are averaged to update the Average Temperature register.
Table 22. ADC Related Registers
Current Measurement
The voltage signal developed across the sense resistor (between SNS1 and SNS2) is differentially sampled by the
ADC inputs via internal 10kΩ resistors connected between SNS1 and IS1, and SNS2 and IS2. Isolating the ADC
inputs (IS1 and IS2 pins) from the sense resistor with 10kΩ facilitates the use of an RC filter by adding a single
external capacitor. The RC filter extends the effective input range beyond ±64mV in pulse-load or pulse-charge
applications. The ADC accurately measures large peak signals as long as the differential signal level at IS1 and
IS2 does not exceed ±64mV.
The Current register reports the average of 128 individual current samples every 88ms. The reported value
represents the average current during the 88ms measurement period. The Average Current register reports the
average of 4096 current samples and is updated every 2.8s.
Figures 11 and 12 specify the update interval and units for the Current and Average Current registers. Values are
posted in two’s compliment format. Positive values represent charge currents (V
represent discharge currents (V
maximum value, 7FFFh. Negative currents below the minimum register value are reported at the minimum value,
8000h.
4
ADDRESS
WORD
600Ah
6003h
6004h
6005h
6006h
6007h
6008h
6009h
Read Only
Read Only
Read Only
Read Only
Read Only
Read Only
ACCESS
R/W
R/W
IS2
> V
Voltage Register
Current Register
Temperature Register
Accumulated Current Register
Accumulated Current (Middle Word)
Accumulated Current (Lower Word)
Average Current Register
ADC Configuration Register
IS1
). Positive currents above the maximum register value are reported at the
SAMP
(687µs). Multiple samples are averaged to update the Average
DS2790 Programmable 1-Cell Li-Ion Fuel Gauge and Protector
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IN
pin and analog ground pin AVSS. Individual voltage
DESCRIPTION
IS1
SAMP
> V
(687µs). All samples are
IS2
) and negative values
SAMP
SNS
,