DS2792 Programmable Fuel Gauge with UART Interface

32 of 40

ANALOG-TO-DIGITAL CONVERSION

The DS2792 performs real-time measurements of system temperature, voltage, current, and accumulated current.

The DS2792’s ADC 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

6000h, as shown in Table 13.

The DS2792 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

averaged to report current, average current, and accumulated current values.

The DS2792 measures voltage on three separate inputs. The voltage of the lower cell, VIN1, is reported as the

reported as the difference between the VIN2 and VIN1 pins. The auxiliary voltage, Vx, is reported both as an

absolute value of the difference between the Vx pin and AVSS, and as a ratio metric percentage of the voltage of

averaged to update the voltage measurement registers.

(6.87ms). Multiple samples are averaged to update the average temperature register.

Table 13. ADC Related Registers

WORD

ADDRESS

ACCESS

DESCRIPTION

6000h

Read Only

Vx Voltage Ratiometric

6001h

Read Only

Vx Voltage Absolute

6002h

Read Only

VIN2 Voltage

6003h

Read Only

VIN1 Voltage

6004h

Read Only

Current

6005h

Read Only

Temperature

6006h

R/W

Accumulated Current

6007h

Read Only

Accumulated Current (Middle Word)

6008h

Read Only

Accumulated Current (Lower Word)

6009h

Read Only

Average Current

600Ah

R/W

ADC Configuration

Current Measurement

The voltage signal developed across the sense resistor (between SNS1 and SNS2) is differentially sampled by the

ADC inputs via internal 10k

resistors connected between SNS1 and IS1, and SNS2 and IS2. Isolating the ADC

inputs (IS1 and IS2 pins) from the sense resistor with 10kŸ 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. Figure 17 specifies the update interval and

resolution of the current register. Values are posted in two’s complement format. Positive values represent charge

maximum register value are reported at the maximum value, 7FFFh. Negative currents below the minimum register

value are reported at the minimum value, 8000h.