Linear Technology Demo Circuit 1402A, Быстрый старт

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LTC3577 AND LTC3577-1
6
USING THE LTC3577 SOFTWARE
The LTC3577 program provides control of the mode and
slew rate of the buck regulators, plus controls the inten-
sity and slew rate of the LED boost controller. It also al-
lows the user to view the contents of the status register.
Refer to Figure 3 for an illustration of the LTC3577 con-
trol window.
VIEW LTC3577 PRODUCT PAGE button opens an inter-
net browser and searches the Linear Technology Corpo-
ration web site for information on the LTC3577 when an
internet connection is available.
REG0 through REG3 text box windows display the hexa-
decimal value that has been written to the corresponding
registers.
STATUS REG text box window displays the hexadecimal
value that has been last read from the LTC3577 status
register.
LDO1 and LDO2 EN/DIS buttons enable or disable LDO1
and LDO2 respectively via the I
2
C interface.
BUCK1 through BUCK3 MODE select buttons are used to
individually set each buck regulator into Pulse Skip Mode
for low noise or Burst Mode for high efficiency.
BUCK SW SLEW RATE option buttons are used to
choose one of four slew rates for optimal EMI reduction
or efficiency. Choose “1ns” for optimal efficiency.
HV/SHDN HI/LOW select button is used to turn on or
shutdown the high voltage buck demo board with the
shutdown feature.
PWR_ON HI/LOW select button is used to set the
PWR_ON pin high or low to turn on or off VOUT1,
VOUT2, and VOUT3.
AUTO READ BACK EN/DIS select button is used to auto-
matically update the status register every 250ms when
enabled. When disabled the read register may be updated
by selecting the “Read Back Status” button.
Read Back Status button is used to update the status
register when selected.
AUTO UPDATE EN/DIS select button is used to automati-
cally update the LTC3577 I
2
C registers when any of the
buck or LED buttons or sliders have been changed.
When auto update is disabled, the LTC3577 I
2
C registers
may be updated by selecting the “Update All Registers”
button.
Update All Registers button is used to update all of the
LTC3577 I
2
C write registers when selected.
NOTE: When power is turned off or removed, the I2C registers are re-
set and the LTC3577 control window will not match the actual condi-
tion of the evaluation board. Use the “Update All Registers” button to
set the device to the current settings selected on the LTC3577 control
window.
LED EN/DIS select button is used to enable or disable the
LED boost controller.
BOOST SW SLEW RATE FAST/SLOW button is used to
turn on and off the LED switch faster or slower for opti-
mal efficiency or EMI reduction. Choose “FAST” for op-
timal efficiency.
LED MODE option buttons are used to choose one of
three Boost controller modes. CC Boost mode is a con-
stant current mode where the LED current is controlled
by the LED DAC REG vertical slider. HV Boost mode
regulates the ILED pin to 0.8V to operate the Boost at a
fixed voltage.
HV Boost mode should not be enabled
unless the demo circuit has been modified to support
this mode of operation.
PWM mode allows the LED in-
tensity to be controlled by pulse width modulating the
LEDs based on the LED DAC REG, PWM Numerator,
PWM Denominator, and PWM Clock Speed settings.
NOTE: When in CC Boost or HV Boost LED modes, the PWM controls
are disabled.
GRADATION TIME option buttons set the desired time to
gradate up to or down from the selected intensity when-
ever the LED controller is enabled or disabled.
LED DAC REG vertical slider controls the LED current
from 20uA to 20mA in 64 logarithmic steps. The inten-
sity slider may be adjusted by clicking on the up or down
arrows to increment or decrement by one LSB or by
clicking and dragging the slide pointer. The hex code and
LED current are displayed in the two text boxes below
the slider.
PWM Clock Speed option buttons are used to select the
PWM clock speed. The PWM clock speed is divided by
the PWM denominator to determine the PWM frequency.