Advanced features 27
Two methods are used to determine the impedance value of the cell or battery pack. The first
method uses data from the battery manufacturer or another source and is simply entered into the
Model 2306 from the front panel or over the GPIB bus. The second method involves a simple
series of measurements as follows.
Figure 15
Voltage drop sample (with supplied Li ion battery pack)
NOTE
Figure 15
shows the voltage drop during the transmit portion of the pulse with the
supplied Li ion battery pack. See
Figure 16
for the comparative illustration using the
Model 2306.
Figure 15
shows the transient voltage response at the battery terminals with the handset
battery. Using
Figure 15
, the voltage drop during the transmit portion of the pulse of a GSM
phone with the supplied Li ion battery is 0.348V. Using the pulse current mode of the battery
channel the measured current during the transmit portion of the data frame is I
H
= 1.536A and
the idle portion of the data frame is I
L
= 0.082A. To estimate R
i
from the measured voltage, we
use
:
Using this value for the output impedance setting in the battery channel, the voltage drop
across the output terminals, as shown in
Figure 16
, is 0.360V. This value is in agreement, to
within 3%, with the results obtained with the battery included with the handset.
NOTE
Figure 16
shows the voltage drop during the transmit portion of the pulse of a GSM
phone using the Model 2306 battery channel with output impedance set to 0.24
Ω.
See
Figure 15
for actual Li ion battery results.
VH – VL = 0.348 V
R
i
V
H
V
L
–
I
H
I
L
–
--------------------
0.348
V
1.454
A
-----------------
0.239
Ω
=
=
≅