LTC3613 Datasheet, PDF (26/36 Pages) Linear Technology – 24V, 15A Monolithic Step Down Regulator

LTC3613
APPLICATIONS INFORMATION
Design Example
Consider a step-down converter with V_IN = 6V to 24V, V_OUT
= 1.2V, I_OUT(MAX) = 15A, and f = 350kHz (see Figure 9).
The regulated output voltage is determined by:
V_OUT
=0.6V
•
⎛
⎝⎜
1+
R_FB2
R_FB1
⎞
⎠⎟
Using a 20k resistor from V_OSNS+ to V_OSNS–, the top
feedback resistor is also 20k.
The frequency is programmed by:
R_T
[kΩ]=
41550
f[kHz]
–2.2=
41550
350
–2.2
≈
116.5k
The minimum on-time occurs for maximum V_IN and should
be greater than 65ns, which is the best that the LTC3613
can achieve. The minimum on-time for this application is:
t_ON(MIN) =
V_OUT
V_IN(MAX)
•
f
=
24V
1.2V
• 350kHz
≈
143ns
Set the inductor value to give 40% ripple current at maxi-
mum V_IN:
L=
1.2V
350kHz • 40%• 15A
•
⎛
⎝⎜
1–
1.2V
24V
⎞
⎠⎟
≈ 0.54μH
Select 0.56μH, which is the nearest standard value.
Select the nearest standard value of 115k.
INTV_CC
R_DIV1
52.3k
R_PGD
100k
R_DIV2
10k
350kHz
C_SS
0.1μF
C_ITH1
220pF RITH
28k
SV_IN
PV_IN
PGOOD
V_OUT
LTC3613
V_RNG
SENSE^–
RUN
SENSE⁺
MODE/PLLIN
EXTV_CC
SW
BOOST
TRACK/SS
INTV_CC
ITH
C_ITH2 100pF
R_T
115k
RT
SGND
PGND
V_OSNS+
V_OSNS–
C_DCR R_DCR
0.1μF 3.09k
C_B 0.1μF
L1
0.56μH
D_B
INTV_CC
C_VCC
4.7μF
C_IN2 ⁺
10μF
V_IN
C_IN1 ^{6V TO 24V}
82μF
25V
V_OUT
1.2V
15A
R_FB2
20k
C_OUT2 +
100μF
C_OUT1
330μF
R_FB1
×2
20k
2.5V
×2
3613 F10
100
90 ^{PULSE-SKIPPING}
MODE
80
70
60
FORCED
CONTINUOUS
50
MODE
40
30
20
10
0
0.1
V_IN = 12V
V_OUT = 1.2V
1
10
100
LOAD CURRENT (A)
3613 F10a
C_IN1: SANYO 25SVPD82M
C_OUT1: SANYO 2R5TPE330M9
D_B: CENTRAL CMDSH-3
L1: VISHAY IHLP4040DZ-056μH
Figure 9. 1.2V, 15A, 350kHz Step-Down Converter
3613fa
26