Datasheet

LTC3675/LTC3675-1
28
36751fc
For more information www.linear.com/LTC3675
applicaTions inForMaTion
Optional capacitor C
FF
is not needed and may compromise
loop stability.
Buck-Boost Regulator
The buck-boost regulator is an internally compensated
voltage mode regulator that is designed to be used with
a 2.2µH inductor. Recommended inductors are listed in
the Table 8.
The input supply needs to be decoupled with a 10µF
capacitor while the output needs to be decoupled with
a 22µF capacitor. Refer to “Capacitor Selection” in the
Applications Information section for details on selecting
a proper capacitor.
The buck-boost regulator can be programmed via I
2
C. To
program the buck-boost regulator, use sub-address 06h.
The bit format is explained in Table 10.
To ensure loop stability, feedback resistor R1 in Figure 5
should be no greater than 105kΩ. Optional capacitor C
FF
is not needed and may compromise loop stability.
LED Driver
For proper operation the LED driver boost circuit needs
a 10µH inductor. Recommended inductors are listed in
Table 11.
The LED driver also needs a rectifier diode. Recommended
schottky diodes are listed in Table 12.
The LED driver has two registers that can be programmed
via I
2
C. One of the registers is accessed at sub-address
07h and the bit format is as shown in Table 13.
The
rate at which the gradation circuit ramps the LED cur-
rent is set by GRAD[2:0]. GRAD[2:0] sets the time the LED
driver will take to transition through one LSB of LED current.
Table 10. Buck-Boost Regulator Program Register Bit Format
Bit7 Enable Default is ‘0’ which disables the buck-boost. The buck-boost regulator can alternately be enabled via its enable pin.
When enabled via pin, the contents of the I
2
C register program its functionality.
Bit6 x Unused
Bit5 Mode Mode = 0 is PWM mode, Mode = 1 is Burst Mode operation. Default is ‘0.’
Bit4 Slow edge This bit controls the slew rate of the switch node. Default is ‘0’ which enables the switch node to slew at a faster rate
than if the bit were programmed a ‘1.’
Bit3(DAC3)
Bit2(DAC2)
Bit1(DAC1)
Bit0(DAC0)
DAC control These bits are used to program the feedback regulation voltage. Default is ‘1111’ which programs a full-scale voltage of
800mV. Bits ‘0000’ program the lowest feedback regulation of 425mV. A LSB (DAC0) has a bit weight of 25mV.
Table 11. Recommended Inductors for LED Driver
PART NUMBER L(µH) MAX I
DC
(A) MAX DCR (mΩ)
SIZE IN mm (L × W × H)
MANUFACTURER
LPS6225-103M 10 2.1 105
6 × 6 × 2.5
Coilcraft
www.coilcraft.com
IHLP2020BZER10RM01 10 4 184
5.2 × 5.5 × 2
Vishay
www.vishay.com
Table 12. Recommended Schottky Diodes for LED Driver
PART NUMBER I
F
(A) MANUFACTURER
PD3S140 1.0 Diodes Inc.
www.diodes.com
ZLLS1000 1.16 Diodes Inc./Zetex
www.diodes.com
CTLSH1-40M322 1.0 Central Semiconductor
www.centralsemi.com