Datasheet

LTC4090/LTC4090-5
12
4090fc
OPERATION
Introduction
The LTC4090/LTC4090-5 are complete PowerPath™
controllers for battery powered USB applications. The
LTC4090/LTC4090-5 are 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. They 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 cur-
rent 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 LTC4090/LTC4090-5 also include 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 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 LTC4090’s Bat-Track maintains ap-
proximately 300mV between the OUT pin and the BAT pin,
while the LTC4090-5 provides a fi xed 5V output.
HVOUT
OUT
GATE
BATBAT
OUT
HVPR
4090 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
30mV
30mV
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