LTC4075XEDD(RevA) 查看數據表（PDF） - Linear Technology
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LTC4075XEDD Datasheet PDF : 16 Pages
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U
OPERATIO
The LTC4075 is designed to efficiently manage charging of
a single-cell lithium-ion battery from two separate power
sources: a wall adapter and USB power bus. Using the
constant-current/constant-voltage algorithm, the charger
can deliver up to 950mA of charge current from the wall
adapter supply or up to 650mA of charge current from the
USB supply with a final float voltage accuracy of ±0.6%.
The LTC4075 has two internal P-channel power MOSFETs
and thermal regulation circuitry. No blocking diodes or
external sense resistors are required.
Power Source Selection
The LTC4075 can charge a battery from either the wall
adapter input or the USB port input. The LTC4075 automati-
cally senses the presence of voltage at each input. If both
power sources are present, the LTC4075 defaults to the
wall adapter source provided sufficient power is present
at the DCIN input. “Sufficient power” is defined as:
• Supply voltage is greater than the UVLO threshold.
• Supply voltage is greater than the battery voltage by
50mV (180mV rising, 50mV falling).
The open drain power status outputs (⎯P⎯W⎯R and USBPWR)
indicate which power source has been selected. Table 1
describes the behavior of these status outputs.
Table 1. Power Source Selection
VDCIN > 4.15V and
VDCIN > BAT + 50mV
VUSBIN > 3.95V and
VUSBIN > BAT + 50mV
Device powered from
wall adapter source;
USBIN current < 25µA
⎯P⎯W⎯R: LOW
USBPWR: LOW
VDCIN < 4.15V or
VDCIN < BAT + 50mV
Device powered from
USB source;
⎯P⎯W⎯R: LOW
USBPWR: Hi-Z
VUSBIN < 3.95V or
VUSBIN < BAT + 50mV
Device powered from
wall adapter source
⎯P⎯W⎯R: LOW
USBPWR: LOW
No charging
⎯P⎯W⎯R: Hi-Z
USBPWR: LOW
LTC4075/LTC4075X
Programming and Monitoring Charge Current
The charge current delivered to the battery from the wall
adapter supply is programmed using a single resistor
from the IDC pin to ground. Likewise, the charge current
from the USB supply is programmed using a single resis-
tor from the IUSB pin to ground. The program resistor
and the charge current (ICHRG) are calculated using the
following equations:
RIDC
=
1000V
ICHRG−DC
, ICHRG−DC
=
1000V
RIDC
RIUSB
=
1000V
ICHRG−USB
,
ICHRG−USB
=
1000V
RIUSB
Charge current out of the BAT pin can be determined at
any time by monitoring the IDC or IUSB pin voltage and
using the following equations:
IBAT
=
VIDC
RIDC
•1000, (charging
fromwall adapter)
IBAT
=
VIUSB
RIUSB
•1000, (charging
fromUSB supply)
Programming Charge Termination
The charge cycle terminates when the charge current falls
below the programmed termination threshold during con-
stant-voltage mode. This threshold is set by connecting an
external resistor, RITERM, from the ITERM pin to ground.
The charge termination current threshold (ITERMINATE) is
set by the following equation:
RITERM
=
100V
ITERMINATE
, ITERMINATE
=
100V
RITERM
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