Datasheet
LTC4089-3
11
40893f
For more information www.linear.com/4089-3
OPERATION
The LTC4089-3 is a complete PowerPath™ controller
for battery-powered USB applications. The LTC4089-3
is designed to receive power from a low voltage source
(e.g., USB or 5V wall adapter), a high voltage source (e.g.,
Firewire/IEEE1394, automotive battery, 12V wall adapter,
etc.), and a single-cell Li-Ion battery. It can then deliver
power to an application connected to the OUT pin and a
battery connected to the BAT pin (assuming that an external
supply other than the battery is present). Power supplies
that have limited current resources (such as USB V
BUS
supplies) should be connected to the IN pin which has a
programmable current limit. Battery charge current will
be adjusted to ensure that the sum of the charge current
and load current does not exceed the programmed input
current limit (see Figure 1).
An ideal diode function provides power from the battery
when output / load current exceeds the input current limit or
when input power is removed. Powering the load through
the ideal diode instead of connecting the load directly to
the battery allows a fully charged battery to remain fully
charged until external power is removed. Once external
power is removed the output drops until the ideal diode is
forward biased. The forward biased ideal diode will then
provide the output power to the load from the battery.
The LTC4089-3 also includes a high voltage switching
regulator which has the ability to receive power from a high
voltage input. This input takes priority over the USB V
BUS
input (i.e., if both HVIN and IN are present, load current
and charge current will be delivered via the high voltage
path). When enabled, the high voltage regulator regulates
the HVOUT voltage using a 750kHz constant frequency,
current mode regulator. An external PFET between HVOUT
(drain) and OUT (source) is turned on via the HVPR pin
allowing OUT to charge the battery and/or supply power
to the application. The LTC4089-3 maintains approximately
300mV between the OUT pin and the BAT pin.
(Refer to Block Diagram)
HVOUT
OUT
GATE
BATBAT
OUT
HVPR
40893 F01
–
+
EDA
D1
L1
CC/CV REGULATOR
CHARGER
HIGH VOLTAGE
BUCK REGULATOR
USB CURRENT LIMIT
ENABLE
–
+
–
+
C1
HVIN
IN
Q1
SW
25mV
25mV
IDEAL
DIODE
4.25V (RISING)
3.15V (FALLING)
75mV (RISING)
25mV (FALLING)
+
LOAD
LI-ION
+
–
+
–
+
–
21
12
11
10
13
7
18
19
Figure 1. Simplified PowerPath Block Diagram