LTC4075 LINER [Linear Technology], LTC4075 Datasheet - Page 9

• Manufacturer Part Number: LTC4075
• Description: Dual Input USB/AC Adapter Standalone Li-Ion Battery Chargers
• Manufacturer: LINER [Linear Technology]

OPERATIO
The LTC4075 is designed to effi ciently 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 fi nal fl oat 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 suffi cient power is present
at the DCIN input. “Suffi cient power” is defi ned as:
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
V
V
V
V
DCIN
DCIN
DCIN
DCIN
• Supply voltage is greater than the UVLO threshold.
• Supply voltage is greater than the battery voltage by
50mV (180mV rising, 50mV falling).
> 4.15V and
> BAT + 50mV
< 4.15V or
< BAT + 50mV
U
V
V
Device powered from
wall adapter source;
USBIN current < 25µA
⎯ P ⎯ W ⎯ R : LOW
USBPWR: LOW
Device powered from
USB source;
⎯ P ⎯ W ⎯ R : LOW
USBPWR: Hi-Z
USBIN
USBIN
> 3.95V and
> BAT + 50mV
V
V
Device powered from
wall adapter source
⎯ P ⎯ W ⎯ R : LOW
USBPWR: LOW
No charging
⎯ P ⎯ W ⎯ R : Hi-Z
USBPWR: LOW
USBIN
USBIN
< 3.95V or
< BAT + 50mV
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 (I
following equations:
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:
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, R
The charge termination current threshold (I
set by the following equation:
I
I
R
R
R
BAT
BAT
ITERM
IDC
IUSB
=
=
=
=
R
R
V
V
I
=
CHRG DC
IDC
IUSB
IDC
IUSB
I
1000
CHRG USB
I
TERMINATE
1000
•
100
−
1000
•
LTC4075/LTC4075X
V
−
1000
ITERM
V
V
,
I
, ( arg
CHRG DC
, ( arg
,
ch
, from the ITERM pin to ground.
I
,
ch
CHRG USB
I
CHRG
TERMINATE
−
ing fromwall adapter
−
) are calculated using the
ing fromUSB
=
1000
R
=
IDC
=
1000
R
R
V
IUSB
100
ITERM
V
TERMINATE
V
sup
ply
)
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)
9
) is