AN2681 Freescale Semiconductor / Motorola, AN2681 Datasheet - Page 13

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

5 Experimental Battery Discharge Data
Using the code presented here and the scenario described here, battery voltage readings were taken every
few minutes from the battery gauge over the 1-Wire interface with the load current held at a constant
value. Data for two values of the current, 500 mA and 250 mA, are presented in Table 6.
5.1 500 mA Current
The battery voltage was read every 15 minutes, and the potentiometer was set to such a value as to draw a
load current of 500 mA. Table 6 lists the amount of time elapsed since the battery was connected to the
circuit, and the battery voltage was read from the DS2751.
No voltage is seen across the battery terminals after the voltage drops below 2.6 V, because of the
protection circuit built-in to the battery. At the same point, the DS2751 also shuts down, since its
threshold voltage for operation is 2.5 V.
5.2 250 mA Current
To obtain a different discharging curve, the load current was held at 250 mA. Using the stopwatch timer
in the i.MX21, the battery voltage was read from the DS2751 every 5 minutes. The following table lists
the voltage values observed over time.
MOTOROLA
Table 6.
Elapsed Time (Minutes)
Freescale Semiconductor, Inc.
Battery Voltage During Discharge with 500 mA Current
For More Information On This Product,
105
120
135
150
165
180
195
200
15
30
45
60
75
90
0
MC9328MX21 Application Note
Go to: www.freescale.com
Battery Voltage (V)
Experimental Battery Discharge Data
4.19
4.01
3.95
3.90
3.84
3.80
3.75
3.66
3.54
3.38
3.23
3.00
2.80
2.58
0
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