LTC4088-1_12 LINER [Linear Technology], LTC4088-1_12 Datasheet - Page 10

• Manufacturer Part Number: LTC4088-1_12
• Description: High Efficiency Battery Charger/USB Power Manager
• Manufacturer: LINER [Linear Technology]

OR WALL
ADAPTER
LTC4088-1/LTC4088-2
operaTion
Introduction
The LTC4088-1/LTC4088-2 includes a PowerPath control-
ler, battery charger, internal ideal diode, external ideal diode
controller and a SUSPEND LDO. Designed specifically for
USB applications, the PowerPath controller incorporates a
precision average input current limited step-down switch-
ing regulator to make maximum use of the allowable USB
power. Because power is conserved, the LTC4088-1/
LTC4088-2 allows the load current on V
current drawn by the USB port without exceeding the USB
load specifications.
The switching regulator and battery charger communicate
to ensure that the average input current never exceeds the
USB specifications.
The ideal diodes from BAT to V
power is always available to V
ficient or absent power at V
Finally, to prevent battery drain when a device is con-
nected to a suspended USB port, an LDO from V
V
current to the application.
Input Current Limited Step Down Switching Regulator
The power delivered from V
by a 2.25MHz constant frequency step-down switching
10
TO USB
OUT
provides either low power or high power suspend
11
2
I
V
SWITCH
CLPROG
BUS
1.188V
/N
AVERAGE INPUT
CURRENT LIMIT
CONTROLLER
–
+
BUS
GATE DRIVE
BUS
PWM AND
OUT
OUT
.
to V
even if there is insuf-
guarantee that ample
AVERAGE OUTPUT
OUT
VOLTAGE LIMIT
OUT
CONTROLLER
to exceed the
is controlled
–
+
+
3.6V
BUS
CONSTANT CURRENT
CONSTANT VOLTAGE
BATTERY CHARGER
0.3V
+ –
to
Figure 1
regulator. To meet the USB maximum load specification,
the switching regulator contains a measurement and
control system that ensures that the average input cur-
rent remains below the level programmed at CLPROG.
V
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
from V
the ideal diodes even when the battery charger is enabled.
The current at CLPROG is a precise fraction of the V
current. When a programming resistor and an averaging
OUT
drives the combination of the external load and the
BUS
IDEAL
DIODE
15mV
OV
, load current will be drawn from the battery via
–
+
+
–
OUT
V
GATE
V
OUTS
BAT
OUT
SW
exceeds the programmed power
12
10
3
8
9
408812 F01
+
SINGLE CELL
Li-Ion
EXTERNAL
IDEAL DIODE
PMOS
SYSTEM LOAD
3.5V TO
(BAT + 0.3V)
40881fc
OUT
BUS