AS3658 datasheet(60/158 Pages) AMSCO

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AS3658

Data Sheet Confidential - Detail ed Descri ption-Power Management Functions

The key building block of the VFC is an integrator. It will integrate the voltage VSNS across input pins ISENSP and

ISENSN. If VSNS is positive (battery is charged), the output voltage of the integrator increases; a negative input voltage

(battery is discharged) will cause the integrator output voltage to decrease.

Table 50. Fuel Gauge parameters

Symbol

Parameter

Min

Typ

Max

Unit

Note

Charge Current Accumulator

The output signals of the charge count dividers are used as inputs for the charge current accumulator that is realized

as a 15-bit up-down counter with separate inputs for incrementing and decrementing the counter. An additional sign bit

indicates the polarity of the counter value that is maintained in two’s complement format. The current accumulator is

updated at a rate equivalent to one count per 3.05µVh, which is equivalent to one count per 61.03µAh when using a

50m

Ω current sense resistor. It will roll over beyond (7FFF)h when incremented and (0000)h when decremented, and

the value given by the counter will be ambiguous in that case. It is the responsibility of the host to read the counter

before rollover occurs.

The content of the charge current accumulator will be transferred into the DeltaCharge register when the UpdReq bit in

the FuelGauge register has been set. The update of the register has to be synchronized to the sample clock fVFC and

can take up to 1.5 clock cycles (max. 2.5µs). After the registers have been updated successfully, the UpdReq bit is

cleared automatically and the charge current accumulator together with the sign bit will be reset.

Elapsed Time Counter

The sample clock fVFC of the fuel gauge circuit is fed to a 14-bit clock count divider. Its output signal is used as a

clocking signal for the 16-bit elapsed time counter, resulting in an equivalent rate of 1.1379 counts per second

(4096.60 counts = 1 hour). The elapsed time counter will rollover beyond (FFFF)h, and the value given by the counter

will be ambiguous in that case. It is the responsibility of the host to read the counter before rollover occurs.

The content of the elapsed time counter will be transferred into the ElapsedTime register when the UpdReq bit in the

FuelGauge register has been set. The update of the register has to be synchronized to the sample clock fVFC and can

take up to 1.5 clock cycles (max. 2.5µs). After the registers have been updated successfully, the UpdReq bit is cleared

automatically and the elapsed time counter will be reset.

Offset Calibration Mode

Although the VFC compensates for the offset of the integrator the fuel gauge features an additional offset calibration

mode to enhance the measurement accuracy even further. By setting the CalReq bit in the FuelGauge register the

integrator is reset and the offset calibration mode is activated. The charge count dividers are bypassed during offset

calibration to allow a faster calibration procedure with adequate resolution. The offset is accumulated during 16 clocks

of the elapsed time counter, the resulting offset calibration value FGOffCal has a resolution of 3.05µV and is

fCLK

Internal reference

clock

fclk_int/

MHz

internal CLK frequency/2

Programmable: 0.8 to 1.15 MHz

fVFC

Sample frequency

fCLK/59

VISENSP

VISENSN

Input voltage

-0.1

0.1

ZISENSP

ZISENSN

Input impedance

4.67

AVFC

Discharge and Charge

gain

91.0

Hz / V

fCLK = 1.1MHz

FRVFC

Fundamental rate

3.05

µVh

VOFF

Uncompensated offset

voltage

-500

500

µV

VOFF,COMP

Compensated offset

voltage

-50

±10

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