LTC3675_15 Datasheet, PDF (26/38 Pages) Linear Technology – 7-Channel Configurable High Power PMIC

LTC3675/LTC3675-1
Applications Information
Switching Regulator Output Voltage and Feedback
Network
The output voltage of the switching regulators is pro-
grammed by a resistor divider connected from the switching
regulator’s output to its feedback pin and is given by V_OUT
= V_FB (1 + R2/R1) as shown in Figure 5. Typical values for
R1 range from 40kΩ to 1MΩ. The buck regulator transient
response may improve with optional capacitor C_FF that
helps cancel the pole created by the feedback resistors
and the input capacitance of the FB pin. Experimentation
with capacitor values between 2pF and 22pF may improve
transient response.
V_OUT
SWITCHING
REGULATOR
(BUCK, BOOST,
BUCK-BOOST) ^FB
R2
C_FF ⁺ C_OUT
(OPTIONAL)
R1
36751 F05
Figure 5. Feedback Components
Buck Regulators
All four buck regulators are designed to be used with
2.2µH inductors. Tables 4 and 5 show the recommended
inductors for the 500mA and 1A buck regulators.
The input supply needs to be decoupled with a 10µF
capacitor while the output needs to be decoupled with
a 22µF capacitor for a 1A buck regulator and 10µF for a
500mA buck regulator. Refer to Capacitor Selection in the
Applications Information section for details on selecting
a proper capacitor.
Each buck regulator can be programmed via I²C. To program
buck regulator 1 (1A) use sub-address 01h, buck regulator 2
(1A) sub-address 02h, buck regulator 3 (500mA) sub-
address 03h and buck regulator4 (500mA) sub-address
04h. The bit format is explained in Table 6.
Combined Buck Regulators
A single 2A buck regulator is available by combining both
1A buck regulators together. Both the 500mA buck regula-
tors may also be combined together to form a 1A buck
regulator. Tables 4 and 7 show the recommended inductors.
The input supply needs to be decoupled with a 22µF
capacitor while the output needs to be decoupled with
Table 4. Recommended Inductors for 1A Buck Regulators and Ganged Buck 3, Buck 4 Application
PART NUMBER
L(µH)
MAX I_DC (A)
MAX DCR (mΩ) SIZE IN mm (L × W × H)
LPS4018-222
2.2
2.8
70
4 × 4 × 1.8
XFL4022-222
2.2
3.5
21.35
4×4×2
LTF5022-2R2
2.2
3.2
36
5 × 5.2 × 2.2
LPS3015-222
2.2
2.0
110
3 × 3 × 1.5
MANUFACTURER
Coilcraft
www.coilcraft.com
Coilcraft
www.coilcraft.com
TDK
www.tdk.com
Coilcraft
www.coilcraft.com
Table 5. Recommended Inductors for 500mA Buck Regulators
PART NUMBER
L(µH)
MAX I_DC (A) MAX DCR (mΩ)
LPS3015-222
2.2
2.0
110
MLPS3015-2R2
2.2
1.4
110
MDT2520-CR2R2
2.2
1.35
90
LQM2HPN2R2
2.2
1.0
120
SIZE IN mm (L × W × H)
3 × 3 × 1.5
3 × 3 × 1.5
2.5 × 2 × 1
2.5 × 2 × 1.1
MANUFACTURER
Coilcraft
www.coilcraft.com
Maglayers
www.maglayers.com
Toko
www.toko.com
Murata
www.murata.com
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For more information www.linear.com/LTC3675
36751fc