ltc4078 Linear Technology Corporation, ltc4078 Datasheet - Page 9

• Manufacturer Part Number: ltc4078
• Description: Dual Input Li-ion Battery Charger With Overvoltage Protection
• Manufacturer: Linear Technology Corporation

OPERATION
The LTC4078/LTC4078X are designed to effi ciently man-
age 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 850mA of charge current
from the USB supply with a fi nal fl oat voltage accuracy of
±0.6%. The LTC4078/LTC4078X have two internal P-chan-
nel power MOSFETs and thermal regulation circuitry. No
blocking diodes or external sense resistors are required.
Power Source Selection
The LTC4078/LTC4078X can charge a battery from ei-
ther the wall adapter input or the USB port input. The
LTC4078/LTC4078X automatically sense the presence of
voltage at each input. If both power sources are present,
the LTC4078/LTC4078X default to the wall adapter source
provided a valid voltage is present at the DCIN input. “Valid
voltage” is defi ned as:
The open-drain power status output (PWR) indicates which
power source has been selected. Table 1 describes the
behavior of this status output.
Programming and Monitoring Charge Current
The charge current delivered to the battery from the wall
adapter or USB supply is programmed using a single re-
sistor from the IDC or IUSB pin to ground. Both program
resistors and charge currents (I
the following equations:
• Supply voltage is greater than the UVLO threshold
• Supply voltage is greater than the battery voltage by
R
R
and less than the OVLO threshold.
40mV.
IDC
IUSB
=
=
I
CHRG DC
I
1000V
CHRG USB
1000V
, I
CHRG DC
, I
CHRG USB
=
CHRG
1000V
R
=
IDC
) are calculated using
1000V
R
IUSB
Charge current out of the BAT pin can be determined at
any time by monitoring the IDC or IUSB pin voltage and
applying the following equations:
Battery Detection
By default, the BATDET pin is pulled high with an internal
resistor, disabling the charger. To enable the charger, the
BATDET pin must be pulled below the V
(typically 1.75V). An external resistor to ground less than
100k (typically 3.9k) located in the battery pack is used to
detect battery presence.
Programming Charge Termination
The charge cycle terminates when the charge current
falls below the programmed termination threshold level
during constant-voltage mode. This threshold is set by
connecting an external resistor, R
pin to ground. The charge termination current threshold
(I
The termination condition is detected using an internal
fi ltered comparator to monitor the ITERM pin. When the
ITERM pin voltage drops below 100mV* for longer than
t
charge current is latched off and the LTC4078/LTC4078X
enter standby mode.
When charging, transient loads on the BAT pin can cause
the ITERM pin to fall below 100mV for short periods of
time before the DC charge current has dropped below the
*Any external sources that hold the ITERM pin above 100mV will prevent the LTC4078X from
terminating a charge cycle.
TERMINATE
TERMINATE
I
I
R
BAT
BAT
ITERM
=
=
R
R
V
V
=
IDC
IUSB
IDC
IUSB
(typically 1.6ms), charging is terminated. The
) is set by the following equation:
I
TERMINATE
• 1000, (charging from wall adapter)
100V
• 1000, (charging from USBsupply)
LTC4078/LTC4078X
, I
TERMINATE
ITERM
=
R
, from the ITERM
100V
ITERM
BDET
threshold
4078xfb
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