LTC3600_15 Datasheet, PDF (17/28 Pages) Linear Technology – 15V, 1.5A Synchronous Rail-to-Rail Single Resistor Step-Down Regulator

LTC3600
Applications Information
Design Example
As a design example, consider using the LTC3600 in an
application with the following specifications:
V_IN = 10.8V to 13.2V
V_OUT = 1.8V
I_OUT(MAX) = 1.5A
I_OUT(MIN) = 500mA
f_SW = 2MHz
First, R_SET is selected based on:
R_SET
=
V_OUT
50µA
=
1.8V
50µA
=
36kΩ
For best accuracy, a 0.1% 36.1k resistor is selected.
Because efficiency is important at both high and low load
current, discontinuous mode operation will be utilized.
Select from the characteristic curves the correct R_T resis-
tor value for 2MHz switching frequency. Based on that,
R_T should be 18.2k. Then calculate the inductor value for
about 40% ripple current at maximum V_IN:
L
=


1.8V
2MHz • 0.6A




1
−
1.8V _
13.2V ^
= 1.3µH
The nearest standard value inductor would be 1.2µH.
C_OUT 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, one
47µF ceramic capacitor will be used.
C_IN should be sized for a maximum current rating of:
I_{R M S}
=
1.5A


1.8V _
13.2V ^


13.2V
1.8V
−
1^{}
1/ 2
=
0.51A
Decoupling the V_IN pin with one 22µF ceramic capacitor
is adequate for most applications.
3600fc
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