BQ24040_16 Datasheet, PDF (29/38 Pages) Texas Instruments – Single Cell Li-Ion and Li-Pol Battery Charger With Auto Start

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bq24040, bq24041, bq24045
SLUS941F – SEPTEMBER 2009 – REVISED MARCH 2015
10 Power Supply Recommendations
The devices are designed to operate from an input voltage supply range between 3.5 V and 28 V and current
capability of at least the maximum designed charge current. This input supply should be well regulated. If located
more than a few inches from the bq24040x IN and GND terminals, a larger capacitor is recommended.
11 Layout
11.1 Layout Guidelines
To obtain optimal performance, the decoupling capacitor from IN to GND (thermal pad) and the output filter
capacitors from OUT to GND (thermal pad) should be placed as close as possible to the bq2405x, with short
trace runs to both IN, OUT and GND (thermal pad).
• All low-current GND connections should be kept separate from the high-current charge or discharge paths
from the battery. Use a single-point ground technique incorporating both the small signal ground path and the
power ground path.
• The high current charge paths into IN terminal and from the OUT terminal must be sized appropriately for the
maximum charge current in order to avoid voltage drops in these traces
• The bq2404x family is packaged in a thermally enhanced MLP package. The package includes a thermal pad
to provide an effective thermal contact between the IC and the printed circuit board (PCB); this thermal pad is
also the main ground connection for the device. Connect the thermal pad to the PCB ground connection. It is
best to use multiple 10mil vias in the power pad of the IC and close enough to conduct the heat to the bottom
ground plane. The bottom ground place should avoid traces that “cut off” the thermal path. The thinner the
PCB the less temperature rise. The EVM PCB has a thickness of 0.031 inches and uses 2 oz. (2.8mil thick)
copper on top and bottom, and is a good example of optimal thermal performance.
11.2 Layout Example
Figure 39. Layout
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