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| LTC3622_15 Datasheet, PDF (18/24 Pages) Linear Technology – 17V, Dual 1A Synchronous Step-Down Regulator with Ultralow Quiescent Current | |||
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LTC3622/
LTC3622-2/LTC3622-23/5
Applications Information
Design Example
As a design example, consider using the LTC3622 in an
application with the following specifications:
VIN1 = VIN1 = 10.8V to 13.2V
VOUT1 = 5V
VOUT2 = 3.3V
IOUT1(MAX) = 1A
IOUT2(MAX) = 1A
IOUT(MIN) = 0
fSW = 2.25MHz
Because efficiency is important at both high and low load
current, Burst Mode operation will be utilized.
Given the internal oscillator of 2.25MHz, we can calculate
the inductors value for about 40% ripple current at maxi-
mum VIN:
L1=

ï£ï£¬
5V
2.25MHz
â¢
0.4A
ï£ï£¬1â
5V
13.2V


=
3.4µH
L2
=

ï£ï£¬
3.3V
2.25MHz â¢
0.4A
ï£ï£¬1â
3.3V
13.2V


=
2.75µH
Using standard value of 3.3µH and 2.7µH for inductors
results in maximum ripple currents of:
ÎIL1
=
5V
2.25MHz â¢
3.3µH
ï£ï£¬1â
5V
13.2V


=
0.42A
ÎIL2
=
3.3V
2.25MHz ⢠2.7µH
ï£ï£¬1â
3.3V
13.2V


=
0.41A
COUT will be selected based on the ESR that is required to
satisfy the output voltage ripple requirement and the bulk
capacitance needed for loop stability. For this design, a
22µF ceramic capacitor will be used.
CIN should be sized for a maximum current rating of:
IRMS1
=
1A

ï£ï£¬
5
13.2


13.2 â 1 = 0.49A
5
IRMS2
=
1A

ï£ï£¬
3.3
13.2


13.2 â 1 = 0.43A
3.3
Decoupling the VIN1 and VIN2 pins with 10µF ceramic
capacitors is adequate for most applications.
VOUT1
5V
1A
VIN
17V MAX
CIN
10µF
3.3µH
COUT1
22µF
22pF 619k
84.5k
VIN1
INTVCC
VIN2 MODE/SYNC
RUN1
RUN2
PHASE
ILIM
LTC3622-2
PGOOD1 PGOOD2
SW2
SW2
FB2 GND FB2
C1
1µF
2.7µH
619k
137k
22pF
VOUT2
3.3V
1A
COUT2
22µF
3622 F04
Figure 4. 5V/3.3V VOUT Burst Mode Operation Application
3622fa
18
For more information www.linear.com/LTC3622
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