LTC3586-1_15 Datasheet, PDF (14/36 Pages) Linear Technology – High Efficiency USB Power Manager with Boost, Buck-Boost and Dual Bucks

LTC3586/LTC3586-1
operation
Introduction
The LTC3586/LTC3586-1 are highly integrated power
management ICs which include a high efficiency switch
mode PowerPath controller, a battery charger, an ideal
diode, an always-on LDO, two 400mA buck switching
regulators, a 1A buck-boost switching regulator, and an
800mA boost switching regulator. All of the regulators can
be independently controlled via ENABLE pins.
Designed specifically for USB applications, the PowerPath
controller incorporates a precision average input current
buck switching regulator to make maximum use of the
allowable USB power. Because power is conserved, the
LTC3586/LTC3586-1 allow the load current on V_OUT to
exceed the current drawn by the USB port without exceed-
ing the USB load specifications.
The PowerPath switching regulator and battery charger
communicate to ensure that the input current never violates
the USB specifications.
The ideal diode from BAT to V_OUT guarantees that ample
power is always available to V_OUT even if there is insufficient
or absent power at V_BUS.
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
up to 20mA.
Along with constant frequency PWM mode, the buck and
the buck-boost switching regulators have a low power
burst mode setting for significantly reduced quiescent
current under light load conditions.
High Efficiency Switching PowerPath Controller
Whenever V_BUS is available and the PowerPath switch-
ing regulator is enabled, power is delivered from V_BUS to
V_OUT via SW. V_OUT drives the combination of the external
load (including switching regulators 1, 2, 3 and 4) and
the battery charger.
If the combined load does not exceed the PowerPath
switching regulator’s programmed input current limit, V_OUT
will track 0.3V above the battery (Bat-Track). By keeping
the voltage across the battery charger low, efficiency is
optimized because power lost to the linear battery char-
ger is minimized. Power available to the external load is
therefore optimized.
If the combined load at V_OUT is large enough to cause the
switching PowerPath supply to reach the programmed
input current limit, the battery charger will reduce its
charge current by that amount necessary to enable the
external load to be satisfied. Even if the battery charge
current is set to exceed the allowable USB current, the USB
specification will not be violated. The PowerPath switch-
ing regulator will limit the average input current so that
the USB specification is never violated. Furthermore, load
current at V_OUT will always be prioritized and only excess
available power will be used to charge the battery.
If the voltage at BAT is below 3.3V, or the battery is not
present, and the load requirement does not cause the
PowerPath switching regulator to exceed the USB
specification, V_OUT will regulate at 3.6V, as shown in
Figure 1. This “instant-on” feature will allow a portable
product to run immediately when power is applied without
waiting for the battery to charge. If the load exceeds the
current limit at V_BUS, V_OUT will range between the no-load
voltage and slightly below the battery voltage, indicated
by the shaded region of Figure 1.
For very low-battery voltages, the battery charger acts like
a load and, due to limited input power, its current will tend
to pull V_OUT below the 3.6V “instant-on” voltage. To prevent
V_OUT from falling below this level, an undervoltage circuit
automatically detects that V_OUT is falling and reduces the
battery charge as needed. This reduction ensures that load
current and output voltages are always priortized while
allowing as much battery charge current as possible. See
Over-Programming the Battery Charger in Applications
Information Section.
The power delivered from V_BUS to V_OUT is controlled by a
2.25MHz constant-frequency buck switching regulator. To
meet the USB maximum load specification, the switching
regulator includes a control loop which ensures that the
average input current is below the level programmed at
CLPROG.
3586fb
14