LTC4089/LTC4089-5
11
40895fc
OPERATION
The LTC4089/LTC4089-5 is a complete PowerPath™
controller for battery powered USB applications. The
LTC4089/LTC4089-5 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 bat-
tery, 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 pres-
ent). 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/LTC4089-5 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 be-
tween 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 maintains
approximately 300mV between the OUT pin and the BAT
pin, while the LTC4089-5 provides a fi xed 5V output.
Input Current Limit
Whenever the input power path is enabled (i.e., SUSP =
0V and HVIN = 0V) and power is available at IN, power
is delivered to OUT. The current limit and charger control
circuits of the LTC4089/LTC4089-5 are designed to limit
(Refer to Block Diagram)
HVOUT
OUT
GATE
BATBAT
OUT
HVPR
4089 F01
–
+
EDA
19
D1
L1
CC/CV REGULATOR
CHARGER
HIGH VOLTAGE
BUCK REGULATOR
USB CURRENT LIMIT
ENABLE
–
+
–
+
21
21
21
C1
HVIN
IN
Q1
SW
25mV
25mV
IDEAL
DIODE
4.25V (RISING)
3.15V (FALLING)
75mV (RISING)
25mV (FALLING)
+
LOAD
LI-ION
+
–
+
–
+
–
Figure 1. Simplifi ed PowerPath Block Diagram
PowerPath is a trademark of Linear Technology Corporation.
