LTC4067 datasheet(18/20 Pages) LINER

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LTC4067

4067f

TYPICAL APPLICATIO S

the PROG pin to the most positive supply rail (IN, BAT or

OUT)(not shown). In low-power shutdown total current

consumption of the LTC4067 is less than 20μA.

Figure 6 illustrates an application for charging single-cell

Li-Ion batteries directly from a USB bus conforming to

the USB requirements for low-power (LPWR), high-power

(HPWR), or self-powered functions. Here, the LTC4067

ensures that the load at OUT sees the USB potential when

the USB port is applied. When the USB port is removed

the load is powered from the battery through an internal

200mΩ ideal diode. Optionally an external PFET driven by

the GATE pin is used to improve performance by reducing

the series resistance.

The 2k resistor at the CLPROG pin ensures that the maxi-

mum current drawn from the USB input port is kept below

the maximum allowed depending on the permitted power

allocation. 500mA for HPWR USB function or 100mA for

LPWR USB function. The LTC4067 is conﬁgured to comply

with the USB SUSPEND speciﬁcation by driving the ILIM0

pin low and the ILIM1 pin high, whereby the load at OUT is

powered from the battery and the only current drawn from

the USB port is due to the two series NTC pin resistors.

The 2k resistor at the PROG pin selects 500mA for the

charge current to automatically charge a single-cell Li-Ion

battery following a constant-current/constant-voltage

(CC/CV) algorithm with a built-in timer that halts charg-

ing after the battery achieves the maximum ﬂoat voltage

of 4.2V. Note that actual charge current depends on the

load current, as the charger shares the USB current with

the load. During a charge cycle the ⎯C⎯H⎯R⎯⎯G pin signals that

the battery is charging in constant-current mode by pull-

ing to GND through an open-drain drive output capable

of driving an LED for visual indication of charge status.

When the charge current drops to less than 10% of the

programmed charge current, and the battery is above the

recharge threshold (4.1V), the ⎯C⎯H⎯R⎯⎯G pin assumes a high

impedance state (but top-off charge current continues to

ﬂow until the internal charge timer elapses). Bad battery

and battery out-of-temperature conditions are also ﬂagged

with the ⎯C⎯H⎯R⎯⎯G pin as described in the Fault Conditions

section.

If the load demands more current than allowed by the USB

current limit, the charge current is automatically scaled

back. Up to the point where an ideal diode function from

BAT to OUT turns on once the OUT voltage drops below the

BAT voltage. When the ideal diode is engaged, the battery

charge cycle is paused and the load at OUT draws current

both from the USB port as well as from the battery.

At any time, the user may monitor both instantaneous

charge current and instantaneous USB current by observ-

ing the PROG pin and CLPROG pin voltages respectively.

When probing these nodes with a capacitive sensor, a series

resistance is recommended to ensure that bulk capacitance

from these two nodes to GND does not exceed 50pF.

Figure 6. USB Battery Charger

LTC4067

OUT

1-CELL

Li-Ion

TO LOAD

OPTIONAL

μF

4067 F06

RPROG

RCLPROG

CHRG

BAT

GATE

NTC

ILIM0

PROG

ILIM1

CLPROG

GND

USB INPUT

μF

SOURCE

DRAIN

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