Datasheet

SAT CHG RIPPLE
I I + (1/2) I³
IN
RIPPLE
S
V D (1 D)
I =
Lf
´ ´ -
´
bq24707
bq24707A
www.ti.com SLUSA78B –JULY 2010– REVISED MARCH 2011
Table 8. Component List for Typical System Circuit of Figure 1
PART DESIGNATOR QTY DESCRIPTION
C1, C2, C3, C13, C14 5 Capacitor, Ceramic, 0.1µF, 25V, 10%, X7R, 0603
C4 1 Capacitor, Ceramic, 100pF, 25V, 10%, X7R, 0603
C5, C6 2 Capacitor, Ceramic, 1µF, 25V, 10%, X7R, 0603
C7 1 Capacitor, Ceramic, 0.047µF, 25V, 10%, X7R, 0603
C8, C9, C10, C11 4 Capacitor, Ceramic, 10µF, 25V, 10%, X7R, 1206
Ci 1 Capacitor, Ceramic, 2.2µF, 25V, 10%, X7R, 1210
Csys 1 Capacitor, Electrolytic, 220µF, 25V
D1 1 Diode, Schottky, 30V, 200mA, SOT-23, Fairchild, BAT54
D2 1 Diode, Schottky, 40V, 120mA, SOD-323, NXP, RB751V40
Q1, Q2, Q5 3 P-channel MOSFET, –30V, –9.4A, SO-8, Vishay Siliconix, Si4435DDY
Q3, Q4 2 N-channel MOSFET, 30V, 12A, PowerPAK 1212-8, Vishay Siliconix, SiS412DN
L1 1 Inductor, SMT, 4.7µH, 5.5A, Vishay Dale, IHLP2525CZER4R7M01
R1 1 Resistor, Chip, 430kΩ, 1/10W, 1%, 0603
R2 1 Resistor, Chip, 66.5kΩ, 1/10W, 1%, 0603
R3, R4, R5, R6, R10 5 Resistor, Chip, 10kΩ, 1/10W, 1%, 0603
R7 1 Resistor, Chip, 316kΩ, 1/10W, 1%, 0603
R8, R12 2 Resistor, Chip, 100kΩ, 1/10W, 1%, 0603
R9 1 Resistor, Chip, 10Ω, 1/4W, 1%, 1206
R11 1 Resistor, Chip, 39.2kΩ, 1/10W, 1%, 0603
R13 1 Resistor, Chip, 3.01MΩ, 1/10W, 1%, 0603
R14 1 Resistor, Chip, 10 Ω, 1/10W, 5%, 0603
R15 1 Resistor, Chip, 7.5 Ω, 1/10W, 5%, 0603
RAC, RSR 2 Resistor, Chip, 0.01Ω, 1/2W, 1%, 1206
Ri 1 Resistor, Chip, 2Ω, 1/2W, 1%, 1210
U1 1 Charger controller, 20 pin VQFN, TI, bq24707RGR or bq24707ARGR
APPLICATION INFORMATION
Negative Output Voltage Protection
Reversely insert the battery pack into the charger output during production or hard shorts on battery to ground
will generate negative output voltage on SRP and SRN pin. IC internal electrostatic-discharge (ESD) diodes from
GND pin to SRP or SRN pins and two anti-parallel (AP) diodes between SRP and SRN pins can be forward
biased and negative current can pass through the ESD diodes and AP diodes when output has negative voltage.
Insert two small resistors for SRP and SRN pins to limit the negative current level when output has negative
voltage. Suggest resistor value is 10Ω for SRP pin and 7-8Ω for SRN pin. After adding small resistors, the
suggested pre-charge current is at least 192mA for a 10mΩ current sensing resistor.
Inductor Selection
The IC has three selectable fixed switching frequencies. Higher switching frequency allows the use of smaller
inductor and capacitor values. Inductor saturation current should be higher than the charging current (I
CHG
) plus
half the ripple current (I
RIPPLE
):
(4)
The inductor ripple current depends on input voltage (V
IN
), duty cycle (D = V
OUT
/V
IN
), switching frequency (f
S
) and
inductance (L):
(5)
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