LTC4075 LINER [Linear Technology], LTC4075 Datasheet - Page 10

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

OPERATIO
LTC4075/LTC4075X
The termination condition is detected by using an internal
fi ltered comparator to monitor the ITERM pin. When the
ITERM pin voltage drops below 100mV
t
charge current is latched off and the LTC4075 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 1.5ms fi lter time
(t
transient loads of this nature do not result in premature
charge cycle termination. Once the average charge current
drops below the programmed termination threshold, the
LTC4075 terminates 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.
Low Battery Charge Conditioning (Trickle Charge)
This feature ensures that near-dead batteries are gradually
charged before reapplying full charge current . If the BAT
10
*Any external sources that hold the ITERM pin above 100mV will prevent the LTC4075 from
terminating a charge cycle.
pin voltage is below 2.9V, the LTC4075 supplies 1/10th
of the full charge current to the battery until the BAT pin
rises back above 2.9V. For example, if the charger is
programmed to charge at 800mA from the wall adapter
input and 500mA from the USB input, the charge current
during trickle charge mode would be 80mA and 50mA,
respectively.
The LTC4075X does not include the trickle charge feature;
it outputs full charge current to the battery when the
BAT pin voltage is below 2.9V. The LTC4075X is useful
in applications where the trickle charge current may be
insuffi cient to supply the load during low battery voltage
conditions.
Automatic Recharge
In standby mode, the charger sits idle and monitors the
battery voltage using a comparator with a 6ms fi lter time
(t
battery voltage falls below 4.1V (which corresponds to
approximately 80%-90% battery capacity). This ensures
that the battery is kept at, or near, a fully charged condi-
TERMINATE
TERMINATE
RECHRG
). A charge cycle automatically restarts when the
(typically 1.5ms), charging is terminated. The
) on the termination comparator ensures that
U
*
for longer than
tion and eliminates the need for periodic charge cycle
initiations.
If the battery is removed from the charger, a sawtooth
waveform of approximately 100mV appears at the battery
output. This is caused by the repeated cycling between
termination and recharge events. This cycling results in
pulsing at the ⎯ C ⎯ H ⎯ R ⎯ G output; an LED connected to this pin
will exhibit a blinking pattern, indicating to the user that
a battery is not present. The frequency of the sawtooth is
dependent on the amount of output capacitance.
Manual Shutdown
The ENABLE pin has a 2MΩ pulldown resistor to GND. The
defi nition of this pin depends on which source is supplying
power. When the wall adapter input is supplying power,
logic low enables the charger and logic high disables it (the
pulldown defaults the charger to the charging state). The
opposite is true when the USB input is supplying power;
logic high disables the charger and logic high enables it
(the default is the shutdown state).
The DCIN input draws 20µA when the charger is in shut-
down. The USBIN input draws 18µA during shutdown if
no power is applied to DCIN, but draws only 10µA when
V
Charge Current Soft-Start and Soft-Stop
The LTC4075 includes a soft-start circuit to minimize
the inrush current at the start of a charge cycle. When a
charge cycle is initiated, the charge current ramps from
zero to full-scale current over a period of 250µs. Likewise,
internal circuitry slowly ramps the charge current from
full-scale to zero in a period of approximately 30µs when
the charger shuts down or self terminates. This minimizes
the transient current load on the power supply during
start-up and shut-off.
Status Indicators
The charge status output ( ⎯ C ⎯ H ⎯ R ⎯ G ) has two states: pull-down
and high impedance. The pull-down state indicates that
the LTC4075 is in a charge cycle. Once the charge cycle
has terminated or the LTC4075 is disabled, the pin state
becomes high impedance. The pull-down state is capable
of sinking up to 10mA.
DCIN
> V
USBIN
.
4075Xf