LTC3675 Datasheet, PDF (28/36 Pages) Linear Technology – 7-Channel Confi gurable High Power PMIC

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 I²C. 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 I²C. 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 I²C 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)
LPS6225-103M
10
2.1
IHLP2020BZER10RM01
10
4
MAX DCR (mΩ)
105
184
SIZE IN mm (L × W × H)
6 × 6 × 2.5
5.2 × 5.5 × 2
MANUFACTURER
Coilcraft
www.coilcraft.com
Vishay
www.vishay.com
Table 12. Recommended Schottky Diodes for LED Driver
PART NUMBER
PD3S140
I_F (A)
1.0
MANUFACTURER
Diodes Inc.
www.diodes.com
ZLLS1000
1.16 Diodes Inc./Zetex
www.diodes.com
CTLSH1-40M322
1.0
Central Semiconductor
www.centralsemi.com
3675f
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