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BQ24140_14 Datasheet, PDF (30/39 Pages) Texas Instruments – Integrated Dual-Input Switch-Mode One-Cell Li-Ion Charger with Full USB Compliance and USB-OTG Support
◁
bq24140
SLUSAO5 – OCTOBER 2011
APPLICATION SECTION
www.ti.com
Charge Current Sensing Resistor Selection Guidelines
Both the termination current range and charge current range depend on the sensing resistor (RSNS). The
termination current step (IOTERM_STEP) can be calculated using Equation 1:
IO(TERM_STEP)
=
VI(TERM0)
R(SNS)
(1)
Table 2 shows the termination current settings for three sensing resistors.
Table 2. Termination Current Settings for 55-mΩ, 68-mΩ, 100-mΩ Sense Resistors
BIT
VI(TERM2)
VI(TERM1)
VI(TERM0)
Offset
VI(TERM) (mV)
13.6
6.8
3.4
3.4
I(TERM) (mA)
R(SNS) = 55mΩ
247
124
62
62
I(TERM) (mA)
R(SNS) = 68mΩ
200
100
50
50
I(TERM) (mA)
R(SNS) = 100mΩ
136
68
34
34
The charge current step (IO(CHARGE_STEP)) is calculated using Equation 2:
IO(CHARGE_STEP)
=
VI(CHRG0)
R(SNS)
(2)
Table 3 shows the charge current settings for three sensing resistors.
Table 3. Charge Current Settings for 55-mΩ, 68-mΩ and 100-mΩ Sense Resistors
BIT
VI(CHRG3)
VI(CHRG2)
VI(CHRG1)
VI(CHRG0)
Offset
VI(REG) (mV)
54.4
27.2
13.6
6.8
37.4
IO(CHARGE) (mA)
R(SNS) = 55mΩ
989
495
247
124
680
IO(CHARGE) (mA)
R(SNS) = 68mΩ
800
400
200
100
550
IO(CHARGE) (mA)
R(SNS) = 100mΩ
544
272
136
68
374
Output Inductor and Capacitance Selection Guidelines
The IC provides internal loop compensation. With the internal loop compensation, the highest stability occurs
when the LC resonant frequency, fo, is approximately 40 kHz (20 kHz to 80 kHz). Equation 3 can be used to
calculate the value of the output inductor, LOUT, and output capacitor, COUT.
1
fo =
2p ´ LOUT ´ COUT
(3)
To reduce the output voltage ripple, a ceramic capacitor with the capacitance between 4.7 μF and 47 μF is
recommended for COUT, see the application section for components selection.
30
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