LTC4056-4.2

13

405642f

TYPICAL APPLICATIO S

USB Charging

The applications shown in Figures 5 and 6 are USB Li-Ion

chargers with automatic PowerPath

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

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 50

µA to

60

µA combined from the USB power port.

The LTC4056 actually regulates the current delivered to

allows the 500mA maximum USB power port consump-

tion to be easily enforced by tying all system loads to the

under 500mA (Figures 5 and 6 are programmed for

100mV (at 500mA).

CHRG

DRIVE

TIMER/SHDN

BAT

GND

8

7

6

5

1

2

3

4

PROG

4056-4.2 F05

Li-Ion

C1

1

µF

C4

4.7

µF

M1

2N7002

ON 0FF

USB

POWER

C3

1

µF

BAT

C2

0.1

µF

Q1

ZXT1M322

M2A

1/2 IRF7329

M2B

1/2 IRF7329

R2

1.87k

R5

0.5

Ω

R1

750

Ω

LTC4056

SENSE

GATE

SYSTEM

LOAD

STAT

GND

CTL

LTC4412

RED

+

R3

470k

CHRG

DRIVE

TIMER/SHDN

BAT

GND

PROG

4056-4.2 F06

Li-Ion

C1

1

µF

C4

4.7

µF

M1

2N7002

ON 0FF

USB

POWER

C3

1

µF

BAT

C2

0.1

µF

Q1

ZXT1M322

M2

Si2315BDS

MBRS130LT3

M3

Si1301DL

GREEN

R2

1.87k

R5

0.5

Ω

R1

750

Ω

8

7

6

5

1

2

3

4

LTC4056

SENSE

GATE

SYSTEM

LOAD

STAT

GND

CTL

LTC4412

RED

+

R3

470k

R4

750

Ω

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.