LTC3605_15 Datasheet, PDF (16/22 Pages) Linear Technology – 15V, 5A Synchronous Step-Down Regulator

LTC3605
Operation
Flood all unused areas on all layers with copper, which
reduces the temperature rise of power components. These
copper areas should be connected to PGND.
Design Example
As a design example, consider using the LTC3605 in an
application with the following specifications:
V_IN = 10.8V to 13.2V, V_OUT = 1.8V, I_OUT(MAX) = 5A,
I_OUT(MIN) = 500mA, f = 2MHz
Because efficiency is important at both high and low load
current, discontinuous mode operation will be utilized.
First select from the characteristic curves the correct R_T
resistor value for 2MHz switching frequency. Based on that
R_T should be 80.6k. Then calculate the inductor value for
about 50% ripple current at maximum V_IN:
L
=
⎛
⎝⎜
1.8V
2MHz • 2.5A
⎞⎠⎟⎛⎝⎜_1–
1.8V
13.2V
⎞
⎠⎟
=
0.31µH
The nearest standard value inductor would be 0.33µH.
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, two
47µF ceramic capacitors will be used.
C_IN should be sized for a maximum current rating of:
I_RMS
=
5A
⎛
⎝⎜
1.8V
13.2V
⎞⎛
⎠⎟⎝⎜
13.2V
1.8V
–
1^{⎞⎠⎟1/2}
=
1.7A
Decoupling the PV_IN pins with two 22µF ceramic capaci-
tors is adequate for most applications.
16
For more information www.linear.com/LTC3605
3605fd