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# BQ24157S View Datasheet(PDF) - Texas Instruments

 Part Name Description Manufacturer BQ24157S 1.55-A Fully Integrated Switch-Mode One-Cell Li-Ion Charger With Full USB Compliance and USB-OTG Support Texas Instruments BQ24157S Datasheet PDF : 45 Pages
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bq24157S
SLUSB76B – FEBRUARY 2013 – REVISED MAY 2015
www.ti.com
9.2.2.1 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 11.
IO(TERM_STEP)
=
VI(TERM0)
R(SNS)
(11)
Table 12 shows the termination current settings for three sensing resistors.
Table 12. Termination Current Settings for 55-m, 68-m, and 100-mSense 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) = 55 m
247
124
62
62
I(TERM) (mA)
R(SNS) = 68 m
200
100
50
50
I(TERM) (mA)
R(SNS) = 100 m
136
68
34
34
For example, with a 68-mΩ sense resistor, V(ITERM2) = 1, V(ITERM1) = 0, and V(ITERM0) = 1, ITERM = [(13.6 mV × 1) +
(6.8 mV × 0) + (3.4 mV × 1) + 3.4 mV] / 68 mΩ = 200 mA + 0 + 50 mA + 50 mA = 300 mA.
The charge current step (IO(CHARGE_STEP)) is calculated using Equation 12.
IO(CHARGE_STEP)
=
VI(CHRG0)
R(SNS)
(12)
Table 13 shows the charge current settings for three sensing resistors.
Table 13. Charge Current Settings for 55-m, 68-m, and 100-mSense 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) = 55 m
989
495
247
124
680
IO(CHARGE) (mA)
R(SNS) = 68 m
800
400
200
100
550
IO(CHARGE) (mA)
R(SNS) = 100 m
544
272
136
68
374
For example, with a 68-mΩ sense resistor, V(CHRG3) = 1, V(CHRG2) = 0, V(ICHRG1) = 0, and V(ICHRG0) = 1, ITERM =
[(54.4 mV × 1) + (27.2 mV × 0) + (13.6 mV × 0) + (6.8 mV × 1) + 37.4 mV] / 68 mΩ = 800 mA + 0 + 0 + 100 mA
= 900 mA.
9.2.2.2 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, ƒo, is approximately 40 kHz (20 to 80 kHz). Equation 13 can be used to
calculate the value of the output inductor, LOUT, and output capacitor, COUT.
1
fo =
2p ´ LOUT ´ COUT
(13)
To reduce the output voltage ripple, TI recommends a ceramic capacitor with the capacitance between 4.7 to 47
μF for COUT. See previous sections in the Detailed Design Procedure for components selection.
32
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