Specifications

LTC4056-4.2
13
405642f
TYPICAL APPLICATIO S
U
USB Charging
The applications shown in Figures 5 and 6 are USB Li-Ion
chargers with automatic PowerPath
TM
control. In order to
comply with USB power specifications a Li-Ion battery
charger must be able to limit the current draw from the
USB power port to 500mA, operate at input voltages as low
as 4.75V (ignoring resistive drops in the cable and connec-
tors which further reduce this value to 4.4V), and have a
low current standby mode.
As described in Undervoltage Charge Current Limiting, the
LTC4056 will automatically reduce charge current if the
input supply voltage reaches V
UVCL
(typically 4.575V).
This feature ideally solves the additional 350mV of resis-
tive drop that the USB power specification requires. If an
LTC4056 is connected to a particularly resistive USB
cable, then charge current will be reduced to ensure that
the input voltage does not drop below the undervoltage
lockout threshold.
The TIMER/SHDN pin can be used to put the LTC4056 into
a low current standby mode. By pulling TIMER/SHDN to
GND, the LTC4056 and LTC4412 will draw about 50µA to
60µA combined from the USB power port.
The LTC4056 actually regulates the current delivered to
the I
SENSE
pin (rather than the BAT pin current). This fact
allows the 500mA maximum USB power port consump-
tion to be easily enforced by tying all system loads to the
I
SENSE
pin and programming the charger to supply just
under 500mA (Figures 5 and 6 are programmed for
490mA). The total impedance between the V
CC
pin and
I
SENSE
pin is typically 0.2Ω, so the maximum drop is just
100mV (at 500mA).
V
CC
I
SENSE
CHRG
DRIVE
TIMER/SHDN
BAT
GND
8
7
6
5
1
2
3
4
PROG
4056-4.2 F05
Li-Ion
C1
1µF
C4
4.7µF
M1
2N7002
ON 0FF
USB
POWER
C3
1µF
BAT
C2
0.1µF
Q1
ZXT1M322
M2A
1/2 IRF7329
M2B
1/2 IRF7329
R2
1.87k
R5
0.5Ω
R1
750Ω
LTC4056
SENSE
GATE
V
IN
SYSTEM
LOAD
STAT
GND
CTL
LTC4412
RED
+
R3
470k
V
CC
I
SENSE
CHRG
DRIVE
TIMER/SHDN
BAT
GND
PROG
4056-4.2 F06
Li-Ion
C1
1µF
C4
4.7µF
M1
2N7002
ON 0FF
USB
POWER
C3
1µF
BAT
C2
0.1µF
Q1
ZXT1M322
M2
Si2315BDS
MBRS130LT3
M3
Si1301DL
GREEN
R2
1.87k
R5
0.5Ω
R1
750Ω
8
7
6
5
1
2
3
4
LTC4056
SENSE
GATE
V
IN
SYSTEM
LOAD
STAT
GND
CTL
LTC4412
RED
+
R3
470k
R4
750Ω
Figure 5. USB Charging and Automatic PowerPath Control with Auxiliary P-Channel MOSFET for Lowest Loss
Figure 6. USB Charging and Automatic PowerPath Control with LTC4412 in Comparator Mode
PowerPath is a trademark of Linear Technology Corporation.