LTC3589 datasheet(45/50 Pages) LINER

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LTC3589/LTC3589-1/

LTC3589-2

3589fe

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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