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BQ25619_V01 Datasheet(Arkusz danych) 45 Page - Texas Instruments

Numer części BQ25619_V01
Szczegółowy opis  BQ25619 I2C Controlled 1-Cell 1.5-A Battery Charger with 20-mA Termination and 1-A Boost Operation
Pobierz  59 Pages
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Producent  TI1 [Texas Instruments]
Strona internetowa  http://www.ti.com
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 45 page
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RIPPLE
COUT
RIPPLE
I
I
0.29
I
2
3
=
»
´
´
CIN
CHG
I
I
D (1 D)
=
´
´
-
IN
RIPPLE
V
D (1 D)
I
fs L
´
´
-
=
´
45
BQ25619
www.ti.com
SLUSDF8A – JUNE 2019 – REVISED JULY 2019
Product Folder Links: BQ25619
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Copyright © 2019, Texas Instruments Incorporated
Typical Application (continued)
9.2.1 Design Requirements
For this design example, use the parameters shown in the table below.
Table 20. Design Parameters
PARAMETER
VALUE
VBUS voltage range
4 V to 13.5 V
Input current limit (REG00[4:0])
2.4 A
Fast charge current limit (RG02[5:0])
1.024 A
Minimum system voltage (REG01[3:1])
3.5 V
Battery regulation voltage (REG04[7:3])
4.2 V
9.2.2 Detailed Design Procedure
9.2.2.1 Inductor Selection
The 1.5-MHz switching frequency allows the use of small inductor and capacitor values to maintain an inductor
saturation current higher than the charging current (ICHG) plus half the ripple current (IRIPPLE):
ISAT ≥ ICHG + (1/2) IRIPPLE
(2)
The inductor ripple current depends on the input voltage (VVBUS), the duty cycle (D = VBAT/VVBUS), the switching
frequency (fS) and the inductance (L).
(3)
The maximum inductor ripple current occurs when the duty cycle (D) is 0.5 or approximately 0.5. Usually inductor
ripple is designed in the range between 20% and 40% maximum charging current as a trade-off between
inductor size and efficiency for a practical design.
For compact solution size and efficiency at high current, 1 µH inductor is recommended. To achieve better light
load efficiency during boost mode (output current below 500mA) , the device also supports 2.2 µH inductor with
10 µF (min) cap on system.
9.2.2.2 Input Capacitor and Resistor
Design input capacitance to provide enough ripple current rating to absorb input switching ripple current. The
worst case RMS ripple current is half of the charging current when duty cycle is 0.5. If the converter does not
operate at 50% duty cycle, then the worst case capacitor RMS current ICin occurs where the duty cycle is closest
to 50% and can be estimated using Equation 4.
(4)
Low ESR ceramic capacitor such as X7R or X5R is preferred for input decoupling capacitor and should be
placed to the drain of the high-side MOSFET and source of the low-side MOSFET as close as possible. Voltage
rating of the capacitor must be higher than normal input voltage level. A rating of 25-V or higher capacitor is
preferred for 12-V input voltage. Capacitance of minimum 10 μF is suggested for typical of 1.5-A charging
current.
During high current output over 700 mA in boost mode, a 10 kΩ pull-down resistor on VBUS is recommended to
keep VBUS low in case Q1 BLKFET leakage gets high.
9.2.2.3 Output Capacitor
Ensure that the output capacitance has enough ripple current rating to absorb the output switching ripple current.
Equation 5 shows the output capacitor RMS current ICOUT calculation.
(5)
The output capacitor voltage ripple can be calculated as follows:




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