LTC3589_12 Datasheet, PDF (16/50 Pages) Linear Technology – 8-Output Regulator with Sequencing and I2C

LTC3589/LTC3589-1/
LTC3589-2
OPERATION
INTRODUCTION
The LTC3589 is a complete power management solution
for portable microprocessors and peripheral devices. It
generates a total of eight voltage rails for supplying power
to the processor core, SDRAM, system memory, PC cards,
always-on real-time clock and HDD functions. Supplying
the voltage rails are an always-on low quiescent current
25mA LDO, one 1.6A and two 1A (1.2A for LTC3589-1/
LTC3589-2) step-down regulators, a 1.2A buck-boost
regulator, and three 250mA low dropout regulators. Sup-
porting the multiple regulators is a highly configurable
power-on sequencing capability, dynamic voltage slewing
DAC output voltage control, a pushbutton interface con-
troller, regulator control via an I²C interface, and extensive
status and interrupt outputs.
The LTC3589 operates over an input supply range of 2.7V
to 5.5V. The input supplies for the 250mA LDO regulators
may operate as low as 1.7V to limit power loss at low
output voltages.
The always-on LDO1 provides a resistor programmable
output voltage as low as 0.8V and is capable of supplying
25mA. With only the always-on LDO active the LTC3589
draws just 8μA (typical). Always-on LDO1 will continue to
operate with V_IN levels as low as 2.0V (typical) to maintain
memory and RTC function as long as possible.
Each of the 250mA LDO regulators has unique output
voltage configurations. LDO3 has a fixed 1.8V (2.8V for
LTC3589-1/LTC3589-2) output. LDO4 has four output
levels selectable via the I²C interface. Its possible outputs
are 1.8V, 2.5V, 2.8V, and 3.3V (1.2V, 1.8V, 2.5V, 3.2V for
LTC3589-1/ LTC3589-2). LDO2 has a dynamically slewing
DAC set point reference and an external feedback pin to
set the output voltage range with a resistive divider. Each
LDO draws 60μA (typical) quiescent current.
The LTC3589 includes three internally compensated
constant frequency current mode step-down switching
regulators two capable of supplying 1A of output cur-
rent and one capable of supplying 1.6A. The LTC3589-1/
LTC3589-2 step-down regulators can supply 1.2A, 1.2A,
and 1.6A. Step-down regulator switching frequencies of
2.25MHz or 1.125MHz are independently selected for each
step-down regulator using the I²C command registers.
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The power-on default frequency is 2.25MHz. Each of the
step-down regulators have dynamically slewing DAC input
references and external feedback pins to set output voltage
range. The step-down regulators three operating modes,
pulse-skipping, burst, or forced continuous, are set using
the I²C interface. In pulse-skipping mode the regulator
will support 100% duty cycle. For best efficiency at low
output loads select Burst Mode operation. Forced continu-
ous mode minimizes output voltage ripple at light loads.
The 4-switch buck-boost DC/DC voltage mode converter
generates a user-programmable output voltage rail from
1.8V to 5V. Utilizing a proprietary switching algorithm,
the buck-boost converter maintains high efficiency and
low noise operation with input voltages that are above,
below or equal to the required output rail. The buck-boost
error amplifier uses a fixed 0.8V reference and the output
voltage is set by an external resistor divider. Burst Mode
operation is enabled through the I²C control registers. No
external compensation components are required for the
buck-boost converter.
The reference inputs for the three step-down regulators
and LDO2 are 5-bit D to A converters with up-down ramp-
ing at selectable slew rates. The slew endpoint voltages
and select bits are stored in I²C registers for each DAC.
A select bit in the I²C command registers chooses which
register to use for each target voltage. Variable reference
slew rates from 0.88mV/μs to 7mV/μs are selectable in
the I²C register. Each of the four DACs has independent
voltage, voltage select, and slew rate control registers.
The LTC3589 is equipped with a pushbutton control circuit
that will activate the WAKE output, indicate pushbutton
status via the PBSTAT pin, and initiate a hard reset shut-
down of the regulators. Grounding the ON pin with the
pushbutton for 400ms will force the WAKE pin to release
HIGH. The WAKE pin output can be tied to the enable pin
of the first regulator in a power-on sequence. Once in the
power-on state, subsequent pushes of the button longer
than 50ms are mirrored by the PBSTAT output. Holding
ON LOW for five seconds disables all the regulators, pulls
down the WAKE pin, and pulls down RSTO for one second
to indicate to the processor that a hard reset occurred. All
regulator enables and pushbutton inputs are inhibited for
one second following the hard reset.
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