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R
T2
+
2.5 R
TC
R
TH
R
TC
* 3.5 R
TH
+
2.5 (27.28k) (4.912k)
27.28k * 3.5(4.912k)
+ 33.2k;
R
T1
+
7 R
TH
R
T2
3
ƪ
R
TH
) R
T2
ƫ
+
7 (4.921k) (33.2k)
3 [4.921k ) 33.2k]
+ 10k
(6)
THERMAL CONSIDERATIONS
q(JA) +
T
J
* T
A
P
(7)
bq2406x
SLUS689A – JUNE 2006 – REVISED OCTOBER 2006
APPLICATION INFORMATION (continued)
PIN COMPONENTS
IN In most applications, the minimum input capacitance needed is a 0.1 µ F ceramic decoupling
capacitor near the input pin connected to ground (preferably to a grond plane through vias).
The recommended amount of input capacitance is 1 µ F or at least as much as on the
output pin. This added capacitance helps with hot plug transients, input inductance and
initial charge transients.
OUT There is no minimum value for capacitance for this output, but it is recommended to connect
a 1 µ F ceramic capacitor between OUT and ground. This capacitance helps with
termination, and cycling frequency between charge done and refresh charge when no
battery is present. It also helps cancel out any battery lead inductance for long leaded
battery packs. It is recommended to put as much ceramic capacitance on the input as the
output so as not to cause a drop out of the input when charging is initiated.
ISET/BAT For stability reasons, it may be necessary to put a 0.47- µ F capacitor between the ISET and
BAT pin..
STAT1/2 and PG Optional (LED STATUS – See below, Processor Monitored; or no status)
STAT1 Connect the cathode of a red LED to the open-collector STAT1 output, and connect the
anode of the red LED to the input supply through a 1.5 k Ω resistor that limits the current.
STAT2 Connect the cathode of a green LED to the open-collector STAT2 output, and connect the
anode of the green LED to the input supply through a 1.5 k Ω resistor that limits the current.
PG Connect the cathode of an LED to the open-collector PG output, and connect the anode of
the LED to the input supply through a 1.5 k Ω resistor to limit the current.
The bq2406x 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). Full PCB design
guidelines for this package are provided in the application note entitled: QFN/SON PCB Attachment Application
Note (SLUA271 ).
The most common measure of package thermal performance is thermal impedance ( θ
JA
) measured (or
modeled) from the chip junction to the air surrounding the package surface (ambient). The mathematical
expression for θ
JA
is:
Where:
T
J
= chip junction temperature
T
A
= ambient temperature
P = device power dissipation
Factors that can greatly influence the measurement and calculation of θ
JA
include:
• Whether or not the device is board mounted
• Trace size, composition, thickness, and geometry
• Orientation of the device (horizontal or vertical)
• Volume of the ambient air surrounding the device under test and airflow
26
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