LTC3675_15 Datasheet, PDF (17/38 Pages) Linear Technology – 7-Channel Configurable High Power PMIC

LTC3675/LTC3675-1
Operation
The LTC3675/LTC3675-1 have six monolithic synchronous
switching regulators and a dual string boost LED driver and
is designed to operate from a single Li-Ion battery. All of
the switching regulators and the LED driver are internally
compensated and need only external feedback resistors for
regulation. The switching regulators also offer two operat-
ing modes: Burst Mode operation for higher efficiency at
light loads and pulse-skipping/PWM mode. In Burst Mode
operation at light loads, the output capacitor is charged
to a voltage slightly higher than its regulation point. The
regulator then goes into sleep, during which the output
capacitor provides the load current. In sleep most of the
regulator’s circuitry is powered down, helping conserve
battery power. When the output capacitor droops below
its programmed value, the circuitry is powered on and
another burst cycle begins. The sleep time decreases as
load current increases.
All switching regulators and LED driver may be configured
via I²C, providing the user with the flexibility to operate
the LTC3675/LTC3675-1 in the most efficient manner. I²C
commands can also be read back via the I²C port, to ensure
a command was not corrupted during a transmission.
All the regulators can be enabled via I²C commands. The
buck regulators and the buck-boost regulator may also be
enabled via enable pins. The enable pins have two different
enable threshold voltages that depend on the operating state
of the LTC3675/LTC3675-1. With all regulators disabled,
the enable pin threshold is at 650mV. If any regulator
is enabled either by its enable pin or an I²C command,
then the enable pin thresholds are at 400mV. A precision
comparator detects a voltage greater than 400mV on the
enable pin and turns that regulator on. This precision
threshold may be used to sequentially enable regulators.
If all regulators are disabled, all the command registers
are set in their default state.
There are also 2 bytes of data that report any fault condi-
tions on the LTC3675/LTC3675-1 via I²C read back.
Buck Switching Regulator
The LTC3675/LTC3675-1 contain four buck regulators.
Two of the buck regulators are designed to deliver up to
1A load current each while the other two regulators can
deliver up to 500mA each.
The buck regulators can operate in either of two modes. In
pulse-skipping mode, the regulator will skip pulses at light
loads but will operate at a constant frequency of 2.25MHz
at higher loads. In Burst Mode operation, the regulator will
burst at light loads whereas at higher loads it will operate
at constant frequency PWM mode of operation, much the
same as pulse-skipping mode at high load. In shutdown,
an I²C control bit provides the flexibility to either keep the
SW node in a high impedance state or pull the SW node
to GND through a 10k resistor.
The buck regulators have forward and reverse current
limiting, soft-start to limit inrush current during start-up,
short-circuit protection and slew rate control for lower
radiated EMI.
Each buck regulator may be enabled via its enable pin or
I²C. The mode of operation, the feedback regulation volt-
age and switch slew rate can all be controlled via I²C. For
applications that require higher power, buck regulators
may be combined together.
Buck Regulators with Combined Power Stages
Two adjacent buck regulators may be combined in a
master-slave configuration by connecting their SW pins
together and connecting the higher numbered buck’s
FB pin to the input supply. The lower numbered buck is
always the master. The higher numbered buck is a slave
and its enable pin must be tied to ground. In Figure 1, buck
V_IN
SW1
BUCK REGULATOR 1
(MASTER)
EN1
FB1
V_IN
L1
400k
800k
C_OUT
1.2V
2A
V_OUT
SW2
BUCK REGULATOR 2 ^VIN
(SLAVE)
EN2
FB2
36751 F01
Figure 1. Buck Regulators Configured as Master-Slave
36751fc
For more information www.linear.com/LTC3675
17