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L6924U View Datasheet(PDF) - STMicroelectronics

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L6924U Datasheet PDF : 37 Pages
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L6924U
Applications information: charging process
Equation 6
RAC
=
⎜⎜⎝⎛
VBG
IAC
⎟⎟⎠⎞ KPRG
Where VBG is the internal reference equal to 1.23 V, whereas KPRG is a constant equal to
9500.
Figure 11. IAC pin connection
In USB mode (MODE pin high), the RUSB resistor can be selected as:
Equation 7
RUSB
=
⎜⎜⎝⎛
VBG
IUSB
⎟⎟⎠⎞ KPRG
Where VBG and KPRG have the same meaning and value above mentioned.
The charge current in USB mode depends on RUSB as well as the state of the ISEL pin.
When this pin is high, the “high-power” USB mode is selected and the charge current is
determined by the equation 7.
The charge current in USB mode should be set in accordance with the typical USB current
capability (up to 500 mA). If ISEL is low, the “low-power” USB mode is selected and the
charge current is a fifth of the high-power USB mode charge current (up to 100 mA)
During low power USB mode operation, since the charge current is reduced by one fifth, the
maximum charging time is proportionally increased (Section 7.7: Maximum charging time).
Figure 12. IUSB pin connection
Regardless of the operation mode (AC adapter or USB), during the fast-charge phase the
battery voltage increases until it reaches the programmed output voltage (4.2 V). A safety
timer is also present. If the Fast-charge phase does not finish within the programmed time
(see Chapter 7.7: Maximum charging time on page 21), a fault is given.
Doc ID 14716 Rev 2
19/37
 

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