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| BQ24157S Datasheet, PDF (31/45 Pages) Texas Instruments – Full USB Compliance and USB-OTG Support | |||
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Not Recommended for New Designs
www.ti.com
bq24157S
SLUSB76B â FEBRUARY 2013 â REVISED MAY 2015
COUT = 15.8 μF
Select two 0603 X5R 6.3-V 10-μF ceramic capacitors in parallel, that is, Murata GRM188R60J106M.
3. Determine the sense resistor using Equation 9:
R(SNS)
=
V(RSNS)
I(CHARGE)
(9)
The maximum sense voltage across the sense resistor is 85 mV. To get a better current regulation accuracy,
V(RSNS) should equal 85 mV, and calculate the value for the sense resistor.
R(SNS)
=
85mV
1.25A
(10)
R(SNS) = 68 mâ¦
This is a standard value. If it is not a standard value, then choose the next close value and calculate the real
charge current. Calculate the power dissipation on the sense resistor:
P(RSNS) = I(CHARGE) 2 Ã R(SNS)
P(RSNS) = 1.252 Ã 0.068
P(RSNS) = 0.106 W
Select 0402 0.125-W 68-m⦠2% sense resistor, that is, Panasonic ERJ2BWGR068.
For 1.5A application, R(SNS)= 85mV/1.55A = 55 mâ¦
4. Measured efficiency and total power loss with different inductors are shown in Figure 29. SW node and
inductor current waveform are shown in Figure 37.
Battery Charge Efficiency
90
TA = 25°C
89
VBUS = 5 V
VBAT = 3 V
88
87
86
85
84
83
82
500
FDK
TOKO
Inter-Technical
muRata
600 700 800 900 1000 1100 1200 1300
Charge Current (mA)
Battery Charge Loss
800
TA = 25°C
700 VBUS = 5 V
VBAT = 3 V
600
500
400
300
FDK
200
TOKO
Inter-Technical
100
muRata
500 600 700 800 900 1000 1100 1200 1300
Charge Current (mA)
Figure 29. Measured Efficiency and Power Loss
Copyright © 2013â2015, Texas Instruments Incorporated
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