LTC4065 LINER [Linear Technology], LTC4065 Datasheet - Page 10

• Manufacturer Part Number: LTC4065
• Description: High Efficiency Battery Charger/USB Power Manager
• Manufacturer: LINER [Linear Technology]

OR WALL
ADAPTER
LTC4088
operaTion
to ensure that the average input current never exceeds the
USB specifications.
The ideal diodes from BAT to V
Introduction
The LTC4088 includes a PowerPath controller, battery
charger, internal ideal diode, optional external ideal diode
controller, SUSPEND LDO and an always-on 3.3V LDO.
Designed specifically for USB applications, the PowerPath
controller incorporates a precision average input current
limited step-down switching regulator to make maximum
use of the allowable USB power. Because power is con-
served, the LTC4088 allows the load current on V
exceed the current drawn by the USB port without exceed-
ing the USB load specifications.
The switching regulator and battery charger communicate
power is always available to V
ficient or absent power at V
To prevent battery drain when a device is connected to a
suspended USB port, an LDO from V
either low power or high power suspend current to the
application.
Finally, an “always on” LDO provides a regulated 3.3V
from V
used to supply up to 25mA to a system microprocessor.
10
TO USB
OUT
. This LDO will be on at all times and can be
11
2
I
V
SWITCH
CLPROG
BUS
1.188V
/N
AVERAGE INPUT
CURRENT LIMIT
CONTROLLER
–
+
BUS
GATE DRIVE
PWM AND
OUT
OUT
.
even if there is insuf-
guarantee that ample
BUS
AVERAGE OUTPUT
VOLTAGE LIMIT
CONTROLLER
to V
OUT
–
+
+
provides
3.6V
OUT
CONSTANT CURRENT
CONSTANT VOLTAGE
BATTERY CHARGER
0.3V
+ –
to
Figure 1
Input Current Limited Step Down Switching Regulator
The power delivered from V
2.25MHz constant frequency step-down switching regu-
lator. To meet the USB maximum load specification, the
switching regulator contains a measurement and control
system that ensures that the average input current remains
below the level programmed at CLPROG. V
combination of the external load and the battery charger.
If the combined load does not cause the switching power
supply to reach the programmed input current limit, V
will track approximately 0.3V above the battery voltage.
By keeping the voltage across the battery charger at this
low level, power lost to the battery charger is minimized.
Figure 1 shows the power path components.
If the combined external load plus battery charge current
is large enough to cause the switching power supply to
reach the programmed input current limit, the battery
charger will reduce its charge current by precisely the
amount necessary to enable the external load to be satis-
fied. Even if the battery charge current is programmed to
exceed the allowable USB current, the USB specification
for average input current will not be violated; the battery
charger will reduce its current as needed. Furthermore, if
the load current at V
IDEAL
DIODE
15mV
OV
–
+
+
–
OUT
GATE
V
BAT
OUT
SW
exceeds the programmed power
12
10
8
9
BUS
4088 F01
to V
OUT
+
is controlled by a
SINGLE CELL
Li-Ion
OUT
OPTIONAL
EXTERNAL
IDEAL DIODE
PMOS
drives the
SYSTEM LOAD
3.5V TO
(BAT + 0.3V)
4088fb
OUT