ISL6292_06 Datasheet, PDF (17/20 Pages) Intersil Corporation – Li-ion/Li Polymer Battery Charger

ISL6292
V_IN
V_PACK
V_IN
V_PACK
V_IN
V_PACK
Power
Const. Cur
Charge
Current
Constant Voltage
(A)
TIME
Power
Charge
Current
Const. Cur
Res
Limit
Constant Voltage
(B)
TIME
Power
Const. Cur
Charge
Current
Constant Voltage
(C)
FIGURE 27. THE OPERATING CURVES WITH THREE DIFFERENT CURRENT LIMITED ADAPTERS
TIME
Figure 29 shows the actual captured waveforms depicted in
Figure 27 (C). The constant charge current is 750mA. A step
in the adapter voltage during the transition from CC mode to
CV mode is demonstrated.
IREF Programming Using Current-Limited Adapter
The ISL6292 has 10% tolerance for the charge current.
Typically the current-limited adapter also has 10% tolerance.
In order to guarantee proper operation, it is recommended
that the nominal charge current be programmed at least
30% higher than the nominal current limit of the adapter.
Board Layout Recommendations
The ISL6292 internal thermal foldback function limits the
charge current when the internal temperature reaches
approximately +100°C. In order to maximize the current
capability, it is very important that the exposed pad under the
package is properly soldered to the board and is connected
to other layers through thermal vias. More thermal vias and
more copper attached to the exposed pad usually result in
better thermal performance. On the other hand, the number
of vias is limited by the size of the pad. The exposed pads for
the 5x5 and 4x4 QFN packages are able to have 9 and 5
vias respectively. The 3x3 DFN package allows 8 vias be
placed in two rows. Since the pins on the 3x3 DFN package
are on only two sides, as much top layer copper as possible
should be connected to the exposed pad to minimize the
thermal impedance. Refer to the ISL6292 evaluation boards
for layout examples.
CV Mode
CC Mode
Resistance Limit Mode
FIGURE 28. SCOPE CAPTURED WAVEFORMS SHOWING THE
THREE MODES
1 hour
FIGURE 29. SCOPE CAPTURED WAVEFORMS SHOWING THE
CASE THAT THE FULL-LOAD ADAPTER
VOLTAGE IS HIGHER THAN THE CRITICAL
VOLTAGE
17
FN9105.8
November 14, 2006