DS2780 Standalone Fuel Gauge IC

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Figure 12. Cell Model Example Diagram

0°C

10°C

20°C

30°C

40°C

100%

1

2

3

4

Derivative

[ppm / °C]

Active

Empty

Standby

Empty

FULL

Cell

Characterization

data points

Full:

The Full curve defines how the full point of a given cell depends on temperature for a given charge

termination. The application’s charge termination method should be used to determine the table values. The

DS2780 reconstructs the Full line from the cell characteristic table to determine the Full capacity of the battery at

each temperature. Reconstruction occurs in one-degree temperature increments.

Active Empty:

The Active Empty curve defines the variation of the Active Empty Point over temperature. The

Active Empty Point is defined as the minimum voltage required for system operation at a discharge rate based on a

high level load current (one that is sustained during a high power operating mode).

This load current is

programmed as the Active Empty current (IAE) and should be a 3.5s average to correspond to values read from

the Current register. The specified minimum voltage, or Active Empty voltage (VAE), should be a 220ms average

to correspond to values read from the Voltage register. The DS2780 reconstructs the Active Empty line from the

cell characteristic table to determine the Active Empty capacity of the battery at each temperature. Reconstruction

occurs in one-degree temperature increments.

Standby Empty:

The Standby Empty curve defines the variation of the standby empty point over temperature.

The standby empty point is defined as the minimum voltage required for standby operation at a discharge rate

dictated by the application standby current. In typical PDA applications, Standby Empty represents the point that

the battery can no longer support RAM refresh and thus the standby voltage is set by the RAM voltage supply

requirements. In other applications, Standby Empty can represent the point that the battery can no longer support a

subset of the full application operation, such as games or organizer functions on a wireless handset. The standby

load current and voltage are used for determining the cell characteristics but are not programmed into the DS2780.

The DS2780 reconstructs the Standby Empty line from the cell characteristic table to determine the Standby Empty

capacity of the battery at each temperature. Reconstruction occurs in one-degree temperature increments.