LTC4075HVXEDD 查看數據表（PDF） - Linear Technology

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LTC4075HVXEDD

High Voltage Dual Input Li-Ion/Polymer Battery Charger

Linear Technology 

LTC4075HVX

OPERATION

The LTC4075HVX is designed to efficiently manage charg-

ing of a single-cell lithium-ion battery from two separate

power sources: a wall adapter and USB power bus. Us-

ing 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 LTC4075HVX has two internal P-channel power

MOSFETs and thermal regulation circuitry. No blocking

diodes or external sense resistors are required.

Power Source Selection

The LTC4075HVX can charge a battery from either the wall

adapter input or the USB port input. The LTC4075HVX au-

tomatically senses the presence of voltage at each input. If

both power sources are present, the LTC4075HVX defaults

to the wall adapter source provided a valid voltage is pres-

ent at the DCIN input. “Valid voltage” is defined as:

• Supply voltage is greater than the undervoltage lock-

out threshold and less than the overvoltage lockout

threshold.

• Supply voltage is greater than the battery voltage by

40mV.

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.

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)

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 by 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 LTC4075HVX enters

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

programmed termination current. The 1.6ms filter time

(tTERMINATE) on the termination comparator ensures that

transient loads of this nature do not result in premature

charge cycle termination. Once the average charge cur-

rent drops below the programmed termination threshold,

the LTC4075HVX terminates the charge cycle and stops

providing current out of the BAT pin. In this state, any load

on the BAT pin must be supplied by the battery.

*Any external sources that hold the ITERM pin above 100mV will prevent the LTC4075HVX from

terminating a charge cycle.

4075hvxf

9

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