AN2681 Freescale Semiconductor / Motorola, AN2681 Datasheet - Page 15

• Manufacturer Part Number: AN2681
• Description: 1-Wire Interface on the i.MX21 Application Processor
• Manufacturer: Freescale Semiconductor / Motorola

The battery lasts approximately twice as long when the load current is divided by half.
5.3 Estimating Battery Capacity
After the characterization of the battery is complete, the remaining capacity can be calculated using a few
equations. Knowing the FULL
given the most recent voltage reading V, the remaining battery capacity can be estimated as:
The estimated battery capacity for both the 500 mA and 250 mA load currents over the duration of the
discharge are presented in the following plot. The FULL value for both cases is 4.19V, while the
EMPTY
MOTOROLA
500
= 2.42V and EMPTY
Elapsed Time (Minutes)
Capacity = [(V - EMPTY
Freescale Semiconductor, Inc.
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I
255
260
265
270
275
280
285
290
295
300
305
310
315
320
325
330
335
340
345
350
355
360
365
370
375
380
385
390
395
400
405
410
415
and EMPTY
250
= 2.58V.
MC9328MX21 Application Note
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I
values of the battery voltage for a given load current I, and
I
) / (FULL
I
- EMPTY
Battery Voltage (V)
Experimental Battery Discharge Data
3.46
3.44
3.42
3.39
3.36
3.34
3.31
3.28
3.25
3.23
3.20
3.17
3.14
3.11
3.08
3.05
3.02
2.99
2.97
2.94
2.91
2.88
2.85
2.83
2.80
2.77
2.74
2.71
2.67
2.63
2.55
2.42
I
)] x 100%
0
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