Datasheet

LTC4089-3
18
40893f
For more information www.linear.com/4089-3
USB and 5V Wall Adapter Power
Although the LTC4089-3 is designed to draw power from
a USB port, a higher power 5V wall adapter can also be
used to power the application and charge the battery
(higher voltage wall adapters can be connected directly to
HVIN). Figure 5 shows an example of combining a 5V wall
adapter and a USB power input. With its gate grounded
by 1k, P-channel MOSFET MP1 provides USB power to
the LTC4089-3 when 5V wall power is not available. When
5V wall power is available, D1 both supplies power to the
LTC4089-3, pulls the gate of MN1 high to increase the
charge current (by increasing the input current limit),
and pulls the gate of MP1 high to disable it and prevent
conduction back to the USB port.
expected application load current. For robust operation in
fault conditions, the saturation current should be ~2.3A. To
keep efficiency high, the series resistance (DCR) should
be less than 0.1
. Table 1 lists several vendors and types
that are suitable.
Table 1: Inductor Vendors
VENDOR URL
PART
SERIES
INDUCTANCE
(µH)
SIZE
(mm)
Sumida www.sumida.com CDRH5D28 8.2, 10 6
6 3
CDRH6D38 10 7
7 4
TDK www.tdk.com SLF6028T 10 6
6 2.8
Toko www.toko.com D63LCB 10 6.3
6.3 3
Catch Diode
Depending on load current, a 1A to 2A Schottky diode is
recommended for the D1 catch diode. The diode must
have a reverse voltage rating equal to, or greater than,
the maximum input voltage. The ON Semiconductor
MBRM140 and the Diodes Inc. DFLS140/160/240 are
good choices.
High Voltage Regulator Capacitor Selection
Bypass the HVIN pin of the LTC4089-3 circuit with a 1µF,
or higher value ceramic capacitor of X7R or X5R type. Y5V
types have poor performance over temperature and applied
voltage and should not be used. A 1µF ceramic is adequate
to bypass the high voltage input and will easily handle the
ripple current. However, if the input power source has
high impedance, or there is significant inductance due to
long wires or cables, additional bulk capacitance may be
necessary. This can be provided with a low performance
electrolytic capacitor.
Figure 5. USB or 5V Wall Adapter Power
APPLICATIONS INFORMATION
2k1k
MN1
2.87k
59k
IN
PROG
CLPROG
LTC4089-3
BAT
+
MP1
D1
I
CHG
Li-Ion
BATTERY
5V WALL
ADAPTER
850mA I
CHG
USB POWER
500mA I
CHG
40893 F05
Inductor Selection and Maximum Output Current
A good choice for the inductor value is L = 10µH. With
this value the maximum load current will be 1A. The RMS
current rating of the inductor must be greater than the
maximum load current and its saturation current should
be about 30% higher. Note that the maximum load current
will be the programmed charge current plus the largest