ltc3566 Linear Technology Corporation, ltc3566 Datasheet - Page 12

• Manufacturer Part Number: ltc3566
• Description: High Ef?ciency Usb Power Manager Plus 1a Buck-boost Converter
• Manufacturer: Linear Technology Corporation

LTC3566
Introduction
The LTC3566 is a highly integrated power management IC
which includes a high effi ciency switch mode PowerPath
controller, a battery charger, an ideal diode, an always-on
LDO, and a 1A buck-boost switching regulator. The entire
chip is controlled via direct digital inputs.
Designed specifi cally for USB applications, the PowerPath
controller incorporates a precision average input current
step-down switching regulator to make maximum use of
the allowable USB power. Because power is conserved,
the LTC3566 allows the load current on V
the current drawn by the USB port without exceeding the
USB load specifi cations.
The PowerPath switching regulator and battery charger
communicate to ensure that the input current never violates
the USB specifi cations.
The ideal diode from BAT to V
power is always available to V
fi cient 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 25mA.
The LTC3566 also has a general purpose buck-boost
switching regulator, which can be independently enabled
via direct digital control. Along with constant frequency
PWM mode, the buck-boost regulator has a low power
burst-only mode setting for signifi cantly reduced quiescent
current under light load conditions.
High Effi ciency Switching PowerPath Controller
Whenever V
regulator is enabled, power is delivered from V
via SW. V
buck-boost regulator) and the battery charger.
OPERATION
12
OUT
BUS
drives both the external load (including the
OUT
is available and the PowerPath switching
. Drawing very little quiescent current,
BUS
OUT
OUT
.
guarantees that ample
even if there is insuf-
OUT
BUS
to exceed
to V
OUT
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
the voltage across the battery charger low, effi ciency 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 power supply to reach the programmed input
current limit, the battery charger will reduce its charge
current by the amount necessary to enable the external
load to be satisfi ed. Even if the battery charge current is
set to exceed the allowable USB current, the USB specifi ca-
tion will not be violated. The switching regulator will limit
the average input current so that the USB specifi cation
is never violated. Furthermore, load current at V
always be prioritized and only remaining 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 switch-
ing regulator to exceed the USB specifi cation, V
regulate at 3.6V, thereby providing “Instant-On” operation.
If the load exceeds the available power, V
a voltage between 3.6V and the battery voltage. If there
is no battery present when the load exceeds the available
USB power, V
The power delivered from V
by a 2.25MHz constant-frequency step-down switching
regulator. To meet the USB maximum load specifi cation,
the switching regulator includes a control loop which
ensures that the average input current is below the level
programmed at CLPROG.
The current at CLPROG is a fraction (h
current. When a programming resistor and an averaging
capacitor are connected from CLPROG to GND, the voltage
OUT
can drop toward ground.
OUT
is large enough to cause the
BUS
to V
CLPROG
OUT
OUT
–1
is controlled
) of the V
will drop to
OUT
OUT
3566p
OUT
BUS
will
will