DS2438EVKIT+
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END-OF-CHARGE AND DISCONNECT TIMESTAMPS
To demonstrate the DS2438’s end-of-charge timestamp, wire the evaluation board in the charging configuration
shown in Figure 1a, start the demonstration, and then disconnect one side of the load resistor (BAT– or PACK–).
As soon as this is done, the end-of-charge Timestamp Register updates to reflect the end-of-charge time. To
demonstrate the disconnect timestamp feature, simply unplug the RJ-11 cable from the evaluation board. During
the time the cable is unplugged, the displayed values of the Elapsed Time Meter and both Timestamp Registers
become invalid because the software is not able to communicate with the DS2438. When the RJ-11 cable is
plugged back in, the software updates the displayed values to reflect the contents of the DS2438, including the new
Disconnect Timestamp Register value.
CURRENT MEASUREMENT CALIBRATION
The Calibrate Current button on the Meters Screen opens the Calibrate Current Measurement window. This
window gives a real-time demonstration of how current measurements are acquired, corrected and reported using
the DS2438. First, the DS2438 takes an uncorrected measurement of the voltage drop across the current sense
resistor. The DS2438 then adds the contents of the Offset Register to the uncorrected current measurement and
writes the corrected result to the Current Register. The host system then divides the voltage value in the Current
Register by the value of the sense resistor to obtain the measured current.
To calibrate DS2438 current measurements for offset error, follow these steps:
1. Press the Calibrate Current button in the Meters Screen.
2. Reduce the actual current driven through the sense resistor to zero.
3. Set the Offset Register value to 0 and press the Apply button.
4. Set the Offset Register value to -1 times the observed Uncorrected Current value and press the Apply button.
This uncorrected current value is the DS2438’s offset error.
5. The Current Register line should now be reporting 0 LSb, 0mV.
To calibrate DS2438 current measurements for sense resistor variation and the effects of trace resistance, follow
these steps:
6. Force a known current through the sense resistor.
7. Enter a different sense resistor value and click the Apply button.
8. Repeat step 7 until the Current reading shown by the software equals the actual current being forced.
9. Click the OK button to leave the Calibrate Current Measurement window. The DS2438 should now be correctly
calibrated, and the Current Meter on the Meters Screen should now show the actual current flowing through
the sense resistor.
