LTC3589_12 Datasheet, PDF (45/50 Pages) Linear Technology – 8-Output Regulator with Sequencing and I2C

LTC3589/LTC3589-1/
LTC3589-2
APPLICATIONS INFORMATION
Earlier i.MX family processors such as the i.MX31 included
two VSTB pins used for controlling the regulator outputs
for a low voltage standby mode, nominal voltage run mode,
and a higher voltage overdrive mode. The LTC3589 can
be used with these processors using the VSTB input pin
to select between run and standby voltages and using
minimal software overhead to set the overdrive voltage
in I²C command registers.
The default DAC reference value in all xxBTVx registers
is 0x19. This accommodates i.MX processors and others
requiring an overdrive voltage. The value can be increased
up to 0x1F for overdrive or supply margining above the
nominal run voltage. Once programmed into the I²C com-
mand registers xxBTVx two voltage outputs are selected
by the VSTB pin. All voltage levels and changes are fully
controllable using the I²C serial port.
Reference Designs and Drivers
Reference designs, schematics, and software drivers are
available to assist the development of Freescale i.MX53
systems that use the LTC3589. Please contact your local
Linear Technology sales representative for details.
OMAP3 and DaVinci Processor Support
The OMAP3 family of ARM processors has similar require-
ments to the processors described above. The LTC3589 I²C
control can fully accommodate the smart reflex dynamic
voltage control with proper embedded software drivers
tailored to the LTC3589 register mapping. The LTC3589
demo board demonstrates configuring and dynamically
slewing and sequencing the outputs using I²C control. The
same provisions can be incorporated into embedded soft-
ware drivers for the OMAP3 or any other target processor.
Back-Driving LTC3589 Outputs
Multirail processors or board level designs may have
surprise leakage paths between power rails. During a
start-up sequence an LTC3589 regulator output may be
pulled higher than 300mV. This violates the default set-
tings for a LTC3589 and LTC3589-1 start-up sequence.
The LTC3589-2 power up default is to allow its regulators
to enable at any output voltage and is recommended for
designs with rail back-drive conditions.
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