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LTC4068XEDD-4.2 Datasheet Download

Part No.:
LTC4068XEDD-4.2
Download:
Download Datasheet
Description:
[Standalone Linear Li-Ion Battery Charger with Programmable Termination]
File Size:
140 K
Page:
12 Pages
Logo:
Manufacturer:
LINER [ LINEAR TECHNOLOGY ]
PCB Prototype
 LTC4068XEDD-4.2 Datasheet Page:3LTC4068XEDD-4.2 Datasheet Page:4LTC4068XEDD-4.2 Datasheet Page:5LTC4068XEDD-4.2 Datasheet Page:6LTC4068XEDD-4.2 Datasheet Page:8LTC4068XEDD-4.2 Datasheet Page:9LTC4068XEDD-4.2 Datasheet Page:10LTC4068XEDD-4.2 Datasheet Page:11 
LTC4068-4.2/LTC4068X-4.2
OPERATIO
The LTC4068 is a single cell lithium-ion battery charger
using a constant-current/constant-voltage algorithm. It
can deliver up to 950mA of charge current (using a good
thermal PCB layout) with a final float voltage accuracy of
±1%.
The LTC4068 includes an internal P-channel power
MOSFET and thermal regulation circuitry. No blocking
diode or external current sense resistor is required; thus,
the basic charger circuit requires only two external com-
ponents. Furthermore, the LTC4068 is capable of operat-
ing from a USB power source.
Normal Charge Cycle
A charge cycle begins when the voltage at the V
CC
pin rises
above the UVLO threshold level and a 1% program resistor
is connected from the PROG pin to ground. If the BAT pin
is less than 2.9V, the charger enters trickle charge mode.
In this mode, the LTC4068 supplies approximately 1/10th
the programmed charge current to bring the battery volt-
age up to a safe level for full current charging. (Note: The
LTC4068X does not include this trickle charge feature.)
When the BAT pin voltage rises above 2.9V, the charger
enters constant-current mode where the programmed
charge current is supplied to the battery. When the BAT pin
approaches the final float voltage (4.2V), the LTC4068
enters constant-voltage mode and the charge current
begins to decrease. When the charge current drops to the
programmed termination threshold (set by the external
resistor R
TERM
), the charge cycle ends.
Programming Charge Current
The charge current is programmed using a single resistor
from the PROG pin to ground. The charge current out of
the BAT pin is 1000 times the current out of the PROG pin.
The program resistor and the charge current are calcu-
lated using the following equations:
R
PROG
=
1000 V
1000 V
, I
CHG
=
I
CHG
R
PROG
Charge current out of the BAT pin can be determined at any
time by monitoring the PROG pin voltage and using the
following equation:
I
BAT
V
=
PROG
• 1000
R
PROG
U
Programming Charge Termination
The charge cycle terminates when the charge current
falls below the programmed termination threshold. This
threshold is set by connecting an external resistor, R
TERM
,
from the ITERM pin to ground. The charge termination
current threshold (I
TERM)
is set by the following equation:
I
TERM
=
100V I
CHG
R
PROG
100V
=
, R
TERM
=
R
TERM
10 R
TERM
I
TERM
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
t
TERM
(typically 1ms), charging is terminated. The charge
current is latched off and the LTC4068 enters standby
mode where the input supply current drops to 200µA.
(Note: Termination is disabled in trickle charging and
thermal limiting modes.)
I
TERM
can be set to be 1/10th of I
CHG
by shorting the ITERM
pin to the PROG pin, thus eliminating the need for external
resistor R
TERM
. When configured in this way, I
TERM
is
always set to I
CHG
/10, and the programmed charge current
is set by the equation:
500V
500V
I
CHG
=
,R
PROG
=
R
PROG
I
CHG
**
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 to 10% of
the programmed value. The 1ms filter time (t
TERM
) on the
termination comparator ensures that transient loads of
this nature do not result in premature charge cycle termi-
nation. Once the
average
charge current drops below the
programmed termination threshold, the LTC4068 termi-
nates the charge cycle and ceases to provide any current
out of the BAT pin. In this state, any load on the BAT pin
must be supplied by the battery.
The LTC4068 constantly monitors the BAT pin voltage in
standby mode. If this voltage drops below the 4.1V recharge
*
Any external sources that hold the ITERM pin above 100mV will prevent the LTC4068 from
terminating a charge cycle.
**
These equations apply only when the ITERM pin is shorted to the PROG pin.
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