ISL78693 Datasheet, PDF (15/18 Pages) Intersil Corporation – Reverse battery leakage 700nA

ISL78693
full-load voltage. The cell voltage 3.65V uses the assumption that
the pack resistance is 200mΩ. Figure 29A illustrates the adapter
voltage, battery pack voltage, the charge current, and the power
dissipation in the charger respectively in the time domain.
If the battery pack voltage reaches 3.65V before the adapter
reaches point B in Figure 27, a voltage step is expected at the
adapter output when the pack voltage reaches the final charge
voltage. As a result, the charger power dissipation is also
expected to have a step rise. This case is shown in Figure 20 on
page 10 as well as Figure 30C. Under this condition, the worst
case thermal dissipation in the charger happens when the
charger enters the constant voltage mode.
If the adapter voltage reaches the full-load voltage before the
pack voltage reaches 3.65V, the charger will experience the
resistance-limit situation. In this situation, the ON-resistance of
the charger is in series with the adapter output resistance. The
equivalent circuit for the resistance-limit region is shown in
Figure 28B. Eventually, the battery pack voltage will reach 3.65V
because the adapter no-load voltage is higher than 3.65V, then
Figure 28C becomes the equivalent circuit until charging ends. In
this case, the worst-case thermal dissipation also occurs in the
constant current charge mode. Figure 29B shows the I-V curves of
the adapter output, the battery pack voltage, and the cell voltage
for the case VFL = 3.55V. In this case, the full-load voltage is
lower than the final charge voltage (3.65V), but the charger is still
able to fully charge the battery as long as the no-load voltage is
above 3.65V. Figure 29B illustrates the adapter voltage, battery
pack voltage, the charge current, and the power dissipation in
the charger respectively in the time domain.
Based on the previous discussion, the worst-case power
dissipation occurs during the constant current charge mode if the
adapter full-load voltage is lower than the critical voltage given in
Equation 13. Even if that is not true, the power dissipation is still
much less than the power dissipation in the traditional linear
charger. Figures 27 and 28 are scope-captured waveforms to
demonstrate the operation with a current-limited adapter.
The waveforms in Figure 27 are the adapter output voltage
(1V/div), the battery voltage (1V/div), and the charge current
(200mA/div) respectively. The time scale is 1ks/div. The adapter
current is limited to 600mA and the charge current is
programmed to 1A. Note that the voltage difference is only
approximately 200mV and the adapter voltage tracks the battery
voltage in the CC mode. Figure 27 also shows the resistance limit
mode before entering the CV mode.
Figure 28 shows the actual captured waveforms depicted in
Figure 30C. The constant charge current is 750mA. A step in the
adapter voltage during the transition from CC mode to CV mode
is demonstrated.
ADAPTER
CHARGER
VADAPTER ^rDS(ON)
I_LIM
I
VCELL
VPACK
RPACK
BATTERY
PACK
ADAPTER
RO
CHARGER
VADAPTER ^rDS(ON)
VNL
I
VCELL
VPACK
RPACK
BATTERY
PACK
ADAPTER
RO
VNL
CHARGER
VADAPTER
3.65V DC
OUTPUT
I
VCELL
V_PACK
R_PACK
BATTERY
PACK
FIGURE 28A. THE EQUIVALENT CIRCUIT IN THE FIGURE 28B. THE EQUIVALENT CIRCUIT IN THE FIGURE 28C. THE EQUIVALENT CIRCUIT WHEN
CONSTANT CURRENT REGION
RESISTANCE-LIMIT REGION
THE PACK VOLTAGE REACHES
THE FINAL CHARGE VOLTAGE
FIGURE 28. THE EQUIVALENT CIRCUIT OF THE CHARGING SYSTEM WORKING WITH CURRENT-LIMITED ADAPTERS
5.5V
3.65V
V_ADAPTER
V_PACK
V_CELL
3.825V
3.65V
3.45V
V_NL
3.65V
V_ADAPTER
V_CELL
V_PACK
3.65V
3.55V
3.25V
3.175V
500mA
500mA
FIGURE 29A.
FIGURE 29B.
FIGURE 29. THE I-V CHARACTERISTICS OF THE CHARGER WITH DIFFERENT CURRENT LIMITED POWER SUPPLIES
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December 12, 2016