LTC4076 查看數據表（PDF） - Linear Technology
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LTC4076 Datasheet PDF : 16 Pages
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OPERATIOU
The LTC4076 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 LTC4076 has two internal P-channel power MOSFETs
and thermal regulation circuitry. No blocking diodes or
external sense resistors are required.
Power Source Selection
The LTC4076 can charge a battery from either the wall
adapter input or the USB port input. The LTC4076 automati-
cally senses the presence of voltage at each input. If both
power sources are present, the LTC4076 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 output (PWR) indicates that
sufficient power is available. Table 1 describes the behavior
of this status output.
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
PWR: LOW
VDCIN < 4.15V or
VDCIN < BAT + 50mV
Device powered from
USB source;
PWR: LOW
VUSBIN < 3.95V or
VUSBIN < BAT + 50mV
Device powered from
wall adapter source
PWR: LOW
No charging
PWR: Hi-Z
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.
RIDC
=
1000V
ICHRG(DC)
,
ICHRG(DC)
=
1000V
RIDC
LTC4076
Similarly, the charge current from the USB supply is
programmed using a single resistor from the IUSB pin
to ground. Setting HPWR pin to its high state will select
100% of the programmed charge current, while setting
HPWR to its low state will select 20% of the programmed
charge current.
RIUSB
=
1000V
ICHRG(USB)
(HPWR = HIGH)
ICHRG(USB)
=
1000V
RIUSB
(HPWR = HIGH)
ICHRG(USB)
=
200V
RIUSB
(HPWR = LOW)
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
from
wall
adapter)
IBAT
=
VIUSB
RIUSB
•
1000, (charging from USBsupply,
HPWR = HIGH)
IBAT
=
VIUSB
RIUSB
•
200, (charging from USBsupply,
HPWR = LOW)
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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