LTC4067 View Datasheet(PDF) - Linear Technology
Part Name
Description
MFG CO.
'LTC4067' PDF : 20 Pages View PDF
LTC4067
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.
18
USB INPUT
10μF
IN
RCLPROG
2k
CHRG
IN
OUT
SOURCE
OPTIONAL
NTC
GATE
LTC4067
BAT
ILIM0
ILIM1
CLPROG
4067 F06
PROG
GND
1-CELL
Li-Ion
DRAIN
RPROG
2k
Figure 6. USB Battery Charger
TO LOAD
10μF
4067f
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