BQ2406X Datasheet, PDF (25/31 Pages) Texas Instruments – 1A SINGLE-CHIP Li-Ion/Li-Pol CHARGE MANAGEMENT IC WITH THERMAL REGULATION

bq2406x
www.ti.com
APPLICATION INFORMATION
SLUS689 – JUNE 2006
SELECTING INPUT AND OUTPUT CAPACITOR
In most applications, all that is needed is a high-frequency decoupling capacitor on the input power pin. A 1-µF
ceramic capacitor, placed in close proximity to the IN pin and GND pad, works fine. In some applications,
depending on the power supply characteristics and cable length, it may be necessary to increase the input filter
capacitor to avoid exceeding the IN pin maximum voltage rating during adapter hot plug events.
The bq2406x only requires a small output capacitor for loop stability. A 0.47 µF ceramic capacitor placed
between the BAT and ISET pad is typically sufficient.
bq2406x CHARGER DESIGN EXAMPLE
Requirements
• Supply voltage = 5 V
• Safety timer duration of 5 hours for fast charge
• Fast charge current of approximately 750 mA
• Battery temp sense is not used
Calculations
Program the charge current for 750 mA:
R_ISET = [V_(SET)× K_(SET) / I_(OUT)]
from electrical characteristics table. . . V_(SET) = 2.5 V
from electrical characteristics table. . . K_(SET) = 335
R_ISET = [2.5 V × 335 / 0.75 A] = 1.12 kΩ
Selecting the closest standard value, use a 1.13 kΩ resistor connected between ISET (pin 6) and ground.
Program 5-hour safety timer timeout:
R_(TMR) = [T_(CHG) / K_(CHG)]
from the electrical characteristics table. . . K_(CHG) = 0.1 hr / kΩ
K_(TMR) = [5 hrs / (0.1 hr / kΩ)] = 50 kΩ
Selecting the closest standard value, use a 49.9 kΩ resistor connected between TMR (pin 2) and ground.
Disable the temp sense function:
A constant voltage between V_TS1 and V_TS2 on the TS input disables the temp sense function.
from electrical characteristics table. . . V_(TS1) = 30% × V_IN
from electrical characteristics table. . . V_(TS2) = 61% × V_IN
A constant voltage of 50% × Vin disables the temp sense function, so a divide-by-2 resistor divider
connected between Vin and ground can be used. Two 1-mΩ resistors keeps the power dissipated in this
divider to a minimum.
PIN
IN
OUT
COMPONENTS
In most applications, the minimum input capacitance needed is a 0.1 µF 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 µF or at least as much as on the
output pin. This added capacitance helps with hot plug transients, input inductance and
initial charge transients.
There is no minimum value for capacitance for this output, but it is recommended to connect
a 1 µF 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.
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