LTC4067 View Datasheet(PDF) - Linear Technology
Part Name
Description
MFG CO.
'LTC4067' PDF : 20 Pages View PDF
LTC4067
TYPICAL APPLICATIO S
Li-Ion Charger from 5V Wall Adapter with Overvoltage
Protection
Figure 5 illustrates an application where the LTC4067 is
used to charge a single-cell Li-Ion battery from a wall
adapter with built-in overvoltage protection.
Overvoltage protection is achieved with the OVI and OVP
pins of the LTC4067 along with an external PFET in se-
ries with the IN pin. This PFET disconnects the LTC4067
from potentially damaging overvoltage conditions that
are caused by attaching the wrong wall adapter. When
the OVI input senses a voltage greater than VOVTH, the
OVP output is pulled up to disable the PFET. When OVI is
below this threshold, the OVP output is pulled low, turning
on this PFET. In the event that large in-rush currents are
expected, it is recommended that a decoupling capacitor
be placed from OVI to GND. The body diode of this PFET
must be connected so that it is reverse biased when an
overvoltage condition exists.
A 10nF capacitor is recommended to dynamically pull-up on
the gate of Q1 if a fast edge occurs at the wall input during
a hot-plug. In the event that this capacitor is pre-charged
below the OVI rising threshold when a high voltage spike
occurs, the OVP output cannot guarantee turning off Q1
before the IN pin voltage exceeds the absolute maximum
voltage for this pin. This may occur in the event that the
wall input suddenly steps from 5.5V to a higher voltage.
In this case, a zener diode is also recommended to keep
the IN pin voltage to a safe level.
In the example of Figure 5, the input current limit from
the wall adapter is programmed to 1A with a 1k resistor
from CLPROG to GND (assuming ILIM0 and ILIM1 are held
high). And the charge current is programmed to 500mA
via the 2k resistor from the PROG pin to GND.
An optional second external PFET connected between
OUT and BAT serves as a high-performance ideal diode;
to connect the load to the battery with an extremely low
impedance. This ideal diode is controlled by the GATE
output pin whenever the wall adapter is not present or
the load demands more current than is available from
the wall adapter input (Connect the source of the PFET to
OUT and the drain to BAT).
Instantaneous monitoring of both input current and
charge current is achieved by measuring the voltages at
the CLPROG and PROG pins respectively.
Low-power shutdown is engaged by any of the following.
Disabling an external NFET tied in series with the PROG
pin resistor, by floating the PROG pin with a single-pole
switch, by tying RPROG to an open-drain output, by pulling
WALL
ADAPTER
1μF
10nF
Q1
10μF
D1
OPTIONAL
INPUT
CURRENT
MONITOR
Q1, Q2: IFR7404
IN
RCLPROG
1k
OVI
OUT
OVP
CHRG
IN
GATE
LTC4067
SOURCE
Q2
OPTIONAL
DRAIN
LOAD
10μF
NTC
BAT
1-CELL
Li-Ion
PROG
ILIM0
ILIM1
CLPROG
4067 F05
GND
RPROG
2k
CHARGE CURRENT
MONITOR
Q3
ENABLE
Figure 5. Li-Ion Charger/Controller with Overvoltage Protection
4067f
17
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