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Number 2191
Application Note Simulating Battery Impedance
Series with the Model 2302 and 2306
Battery Simulator/Chargers
to 0.00. With the exception of the brief transient at the begin-
Introduction ning and end of the pulse, the voltage drop at the battery termi-
The impedance of cells and battery packs varies according to a nals of the handset is nearly zero. The objective is to maintain
variety of factors, such as, but not limited to, chemistry, mechan- the programmed voltage across the DUT (or in other words,
ical construction, number of charge/discharge cycles, tempera- maintain an effective output impedance of approximately 0.0).
ture, and depth of discharge. In applications using batteries with In reality, batteries do not have zero impedance and the
dynamic or pulsed current loads, the voltage across the DUT voltage drop produced by pulsed current loads may have a sig-
may vary significantly. If the peak load current is high enough, nificant effect on the performance of the device. Figure 2 shows
the voltage drop caused by the impedance of the battery may a simple schematic of a battery, represented by an ideal voltage
compromise the performance of the device, including shutdown source (Vcell), the internal impedance (Ri(t)), connected to a
if the voltage transient is below the operating threshold. This DUT with interconnects having a resistance (Rinterconnect).
phenomenon is common in TDMA and GSM cellular handsets
where the magnitude of the high and low current levels during
RF transmission vary by as much as a factor of 20. In the
absence of any filtering capacitance between the battery and the
RF power amplifier, the handset will shut off if the supply volt- Rinterconnect
age is below the operating threshold for periods as short as sev- I(t)
eral microseconds. The variable impedance output, available
exclusively in the Model 2302/2306 battery simulators, enables
test and design engineers to simulate the transient voltage Ri(t)
Cell or V(t)
response of a battery with pulsed current loads. Battery Pack
+ DUT
Vcell