bq2016

GAS GAUGE IC FOR

HIGH DISCHARGE RATES

SLUS475A– JANUARY 2001 – REVISED NOVEMBER 2002

13

POST OFFICE BOX 655303

• DALLAS, TEXAS 75265

discharge compensation (continued)

The bq2016 adjusts the discharge-compensation efficiency for temperature. At lower temperatures, the

discharge-efficiency factor decreases by 5% for each 10

°C temperature step below 10°C.

FDE (new) = FDE – (5% × N)

where N = number of 10

°C steps below 10°C.

For example at a 1C discharge,

T

> 10°C:

N = 0 and FDE(NEW) = 100%

0

°C < T < 10°C:

N = 1 and FDE(NEW) = 95%

–10

°C < T < 0°C:

N = 2 and FDE(NEW) = 90%

–20

°C < T < –10°C:

N = 3 and FDE(NEW) = 85%

–20

°C < T < –30°C:

N = 4 and FDE(NEW) = 80%

error summary

capacity inaccurate

The LMD is susceptible to error on initialization or if no updates occur. On initialization, the LMD value includes

the error between the programmed full capacity and the actual capacity. This error is present until a valid

discharge occurs and LMD is updated. The other cause of LMD error is battery wear-out. As the battery ages,

the measured capacity must be adjusted to account for changes in actual battery capacity. The bq2016

increments the capacity inaccurate count (CPI) register each time a valid charge occurs and is reset whenever

LMD is updated from the DCR. The counter does not wrap around but stops counting at 255. The capacity

inaccurate flag (CI) is set if LMD has not been updated following 64 valid charges.

display

The bq2016 can directly display capacity information using low-power LEDs. The bq2016 displays the battery

charge as a percentage of the LMD.

The capacity display is also adjusted for the present battery temperature. The temperature adjustment reflects

the available capacity at a given temperature but does not affect the NAC register. Tables 6 and 7 show the

temperature adjustments:

Table 6. Temperature Translation for NiCd

TEMPERATURE

(C)

TEMPERATURE TRANSLATION

(%)

T

≥ 10

100

10

> T ≥ 0

100

0

> T ≥ –10

90

–10

> T ≥ –20

75

T

< –20

50

Table 7. Temperature Translation for NiMH

TEMPERATURE

(C)

TEMPERATURE TRANSLATION

(%)

T

≥ 10

100

10

> T ≥ 0

75

0

> T ≥ –10

40

–10

> T ≥ –20

0

T

< –20

0