LTC4067 Просмотр технического описания (PDF) - Linear Technology
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LTC4067 Datasheet PDF : 20 Pages
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U
OPERATIO
Introduction
The LTC4067 is a complete PowerPath controller for bat-
tery powered USB applications. The LTC4067 is designed
to receive power from a USB source (or a wall adapter)
or a battery. It can then deliver power to an application
connected to the OUT pin and a battery connected to the
BAT pin (assuming that an external supply other than the
battery is present). Power supplies that have limited cur-
rent resources (such as USB VBUS supplies) should be
connected to the IN pin which has a programmable current
limit. Battery charge current will be adjusted to ensure that
the sum of the charge current and the load current does
not exceed the programmed input current limit.
An internal ideal diode function provides power from the
battery when output/load current exceeds the input cur-
rent limit or when the input power is removed. Powering
the load through the ideal diode instead of connecting the
load directly to the battery allows a fully charged battery
to remain fully charged until external power is removed.
Once external power is removed the output drops until
the ideal diode is forward biased. The forward biased
ideal diode will then provide the output power to the load
from the battery.
Furthermore, powering switching regulator loads from the
OUT pin (rather than directly from the battery) results in
shorter battery charge times. This is due to the fact that
switching regulators typically require constant input power.
When this power is drawn from the OUT pin voltage (rather
than the lower BAT pin voltage) the current consumed
by the switching regulator is lower leaving more current
available to charge the battery.
Finally, the LTC4067 provides overvoltage controller circuitry
which, when used in conjunction with an external P-channel
MOSFET, will protect against overvoltage damage if a wall
adapter with greater than 6V output is used. The circuit will
tolerate input voltages up to 13V without damage.
USB PowerPath Controller
The input current limit and charge control circuits of the
LTC4067 are designed to limit input current as well as
control battery charge current as a function of IOUT. OUT
drives the combination of the external load and the bat-
tery charger.
LTC4067
If the combined load does not exceed the programmed
input current limit, OUT will be connected to IN through
an internal 200mΩ P-channel MOSFET.
If the combined load at OUT exceeds the programmed input
current limit, the battery charger will reduce its charge
current by the amount necessary to enable the external
load to be satisfied while maintaining the programmed
input current. Even if the battery charge current is set to
exceed the allowable USB current, the USB specification
will not be violated. The input current limit will ensure that
the USB specification is never violated. Furthermore, load
current at OUT will always be prioritized and only excess
available current will be used to charge the battery.
The current out of the CLPROG pin is a fraction (1/1000th)
of the IN current. When a programming resistor is con-
nected from CLPROG to GND, the voltage on CLPROG
represents the input current:
IIN
=
VCLPROG
RCLPROG
• 1000
The input current limit is programmed by the ILIM0 and
ILIM1 pins (see Table 1 in PIN FUNCTIONS). The LTC4067
can be configured to limit input current to one of several
possible settings as well as be deactivated (USB suspend).
The input current limit will be set by the appropriate servo
voltage and the resistor on CLPROG according to the fol-
lowing expressions:
ILIM (A) = 0 (SUSPEND)
ILIM
=
200V
RCLPROG
(Low
Power)
ILIM
=
1000V
RCLPROG
(High
Power)
ILIM (A) = 2A (CLDIS)
Under worst-case conditions, the USB specification will
not be violated with an RCLPROG of greater than 2.1k.
Current Limit Disable (CLDIS)
When ILIM1 is low and ILIM0 is high, the input current limit
is set to a higher current limit for increased charging and
4067f
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