Datasheet

LTC4089/LTC4089-5
17
40895fc
USB and 5V Wall Adapter Power
Although the LTC4089/LTC4089-5 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/LTC4089-5 when 5V wall power is
not available. When 5V wall power is available, D1 both
supplies power to the LTC4089, 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 effi ciency 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/LTC4089-5 circuit
with a 1μF, or higher value ceramic capacitor of X7R or
X5R type. Y5V types have poor performance over tempera-
ture 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 signifi cant
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
BAT
+
MP1
D1
I
CHG
Li-Ion
BATTERY
5V WALL
ADAPTER
850mA I
CHG
USB POWER
500mA I
CHG
4089 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