ltc3586 Linear Technology Corporation, ltc3586 Datasheet - Page 14

• Manufacturer Part Number: ltc3586
• Description: High Ef? Ciency Usb Power Manager With Boost, Buck-boost And Dual Bucks
• Manufacturer: Linear Technology Corporation

OPERATION
LTC3586
Introduction
The LTC3586 is a highly integrated power management IC
which includes 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 switch-
ing 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 allows the load current on V
current drawn by the USB port without exceeding 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
power is always available to V
or absent power at V
An “always on” LDO provides a regulated 3.3V from avail-
able power at V
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
ing regulator is enabled, power is delivered from V
V
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
will track 0.3V above the battery (Bat-Track). By keeping
14
OUT
via SW. V
BUS
OUT
OUT
is available and the PowerPath switch-
. Drawing very little quiescent current,
drives the combination of the external
BUS
.
OUT
OUT
even if there is insufficient
guarantees that ample
OUT
to exceed the
BUS
OUT
to
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
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
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
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
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
V
automatically detects that V
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
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.
OUT
from falling below this level, an undervoltage circuit
OUT
BUS,
below the 3.6V “instant-on” voltage. To prevent
OUT
V
OUT
OUT
will always be prioritized and only excess
will range between the no-load voltage
will regulate at 3.6V, as shown in Figure
OUT
BUS
OUT
is large enough to cause the
to V
is falling and reduces the
OUT
is controlled by a
3586f