LTC4078 查看數據表（PDF） - Linear Technology

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LTC4078

Dual Input Li-Ion Battery Charger with Overvoltage Protection

Linear Technology 

LTC4078/LTC4078X

OPERATION

The LTC4078/LTC4078X are designed to efficiently 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 final float 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 defined as:

• Supply voltage is greater than the UVLO threshold

and less than the OVLO threshold.

• Supply voltage is greater than the battery voltage by

40mV.

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 (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

applying the following equations:

IBAT

=

VIDC

RIDC

• 1000, (charging

from

wall

adapter)

IBAT

=

VIUSB

RIUSB

• 1000, (charging

from

USBsupply)

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 VBDET threshold

(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, 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

The termination condition is detected using an internal

filtered comparator to monitor the ITERM pin. When the

ITERM pin voltage drops below 100mV* for longer than

tTERMINATE (typically 1.6ms), charging is terminated. The

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.

4078xfb

9

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