LTC3576-1_15 Datasheet, PDF (18/48 Pages) Linear Technology – Switching Power Manager with USB On-the-Go Triple Step-Down DC/DCs

LTC3576/LTC3576-1
OPERATION
Introduction
The LTC3576/LTC3576-1 are highly integrated power man-
agement ICs designed to make optimal use of the power
available from a variety of sources, while minimizing power
dissipation and easing thermal budgeting constraints.
They include a high efficiency bidirectional PowerPath
switching regulator, a controller for an external high volt-
age step-down switching regulator, a battery charger, an
ideal diode, an always-on LDO, an overvoltage protection
circuit and three general purpose step-down switching
regulators. The entire chip is controlled by either direct
digital control or by an I²C serial port or both.
The innovative PowerPath architecture ensures that the
application is powered immediately after external voltage is
applied, even with a completely dead battery, by prioritizing
power to the application.
When acting as a step-down converter, the LTC3576/
LTC3576-1’s bidirectional switching regulator takes
power from USB, wall adapters, or other 5V sources and
provides power to the application and efficiently charges
the battery using Bat-Track. Because power is conserved
the LTC3576/LTC3576-1 allow the load current on V_OUT to
exceed the current drawn by the USB port making maxi-
mum use of the allowable USB power for battery charging.
For USB compatibility the switching regulator includes
a precision average input current limit. The PowerPath
switching regulator and battery charger communicate to
ensure that the average input current never exceeds the
USB specifications.
Additionally, the bidirectional switching regulator can also
operate as a 5V synchronous step-up converter taking
power from V_OUT and delivering up to 500mA to V_BUS
without the need for any additional external components.
This enables systems with USB dual-role transceivers to
function as USB on-the-go dual-role devices. True output
disconnect and average output current limit features are
included for short-circuit protection.
For automotive, firewire, and other high voltage applica-
tions, the LTC3576/LTC3576-1 provide Bat-Track control of
an external LTC step-down switching regulator to maximize
battery charger efficiency and minimize heat production.
When power is available from both the USB and an auxiliary
input, the auxiliary input is given priority.
The LTC3576/LTC3576-1 contain both an internal 180mΩ
ideal diode as well as an ideal diode controller for use
with an optional external P-channel MOSFET. The ideal
diode(s) from BAT to V_OUT guarantee that ample power
is always available to V_OUT even if there is insufficient or
absent power at V_BUS or WALL.
An always-on LDO provides a regulated 3.3V from avail-
able power at V_OUT. Drawing very little quiescent current,
this LDO will be on at all times and can be used to supply
20mA.
The LTC3576/LTC3576-1 feature an overvoltage protection
circuit which is designed to work with an external N-chan-
nel MOSFET to prevent damage to their inputs caused by
accidental application of high voltage.
To prevent battery drain when a device is connected to a
suspended USB port, an LDO from V_BUS to V_OUT provides
either low power or high power USB suspend current to
the application.
The three general purpose switching regulators can be
independently enabled either by direct digital control or
by operating the I²C serial port. Under I²C control, all
three switching regulators have adjustable set points so
that voltages can be reduced when high processor perfor-
mance is not needed. Along with constant frequency PWM
mode, all three switching regulators have automatic Burst
Mode operation and LDO modes for significantly reduced
quiescent current under light load conditions.
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