LTC4011_15 Datasheet, PDF (22/26 Pages) Linear Technology – High Efficiency Standalone Nickel Battery Charger

LTC4011
Applications Information
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TOC
Figure 10. Charging Waveforms Example
TIMER CHEM ^VTEMP
10
4
7
BATTERY
PACK
+
NC
66.5k
10k
1200mAhr
NTC
NiCd CELLS
CHEM ^VTEMP
4
7
V_CELL
8
BATTERY
PACK
+
10k
R2
1500mAhr
NTC
NiMH CELLS
–
4011 F11
Figure 11. NiCd Battery Pack with Time Limit Control
–
4011 F12
Figure 12. NiMH Battery Pack Indicating Number of Cells
A second possibility is to configure an LTC4011-based
charger to accept battery packs with varying numbers of
cells. By including R2 of the average cell voltage divider
network shown in Figure 3, battery-based programming
of the number of series-stacked cells could be realized
without defeating LTC4011 detection of battery insertion
or removal. Figure 12 shows a 2-cell NiMH battery pack
that programs the correct number of series cells when it is
connected to the charger, along with indicating chemistry
and providing temperature information.
Any of these battery pack charge control concepts could be
combined in a variety of ways to service custom application
needs. Charging parallel cells is not recommended.
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PCB Layout Considerations
To prevent magnetic and electrical field radiation and
high frequency resonant problems, proper layout of the
components connected to the LTC4011 is essential. Refer
to Figure 13. For maximum efficiency, the switch node
rise and fall times should be minimized. The following
PCB design priority list will help ensure proper topology.
Layout the PCB using this specific order.
1. Input capacitors should be placed as close as possible
to switching FET supply and ground connections with
the shortest copper traces possible. The switching
FETs must be on the same layer of copper as the input
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