LTC3862 Datasheet, PDF (32/40 Pages) Linear Technology – Multi-Phase Current Mode Step-Up DC/DC Controller

LTC3862
APPLICATIONS INFORMATION
45.3k
10nF
4.7nF
30.1k
100pF
12.4k
475k
V_OUT
D_MAX
SLOPE
3V8
SENSE1⁺
BLANK
PHASEMODE SENSE1^–
FREQ
RUN
SS
LTC3862 ^VIN
ITH
FB
SGND
INTV_CC
GATE1
PGND
CLKOUT
SYNC
PLLFLTR
GATE2
SENSE2^–
SENSE2⁺
V_IN
5V TO 36V
L1
18.7μH
PB2020-223
1nF
10Ω
10nF
24.9k
1μF
84.5k
4.7μF
6.8μF 50V
6.8μF 50V
6.8μF 50V
10Ω
10nF
L2
18.7μH
PB2020-223
D1
30BQ060
Q1
HAT2266H
0.008Ω
1W
100μF
63V
100μF _{10μF 50V}
63V
0.008Ω
1W
Q2
HAT2266H
D2
30BQ060
10μF 50V
10μF 50V
10μF 50V
V_OUT
48V
5A (MAX)
3862 F25a
Figure 25a. A 5V to 36V Input, 48V/5A Output 2-Phase Boost Converter Application Circuit
6
5
4
3
2
1
0
0
10
20
30
40
INPUT VOLTAGE (V)
3862 F25b
Figure 25b. Output Current vs Input Voltage
4. A ripple current of 40% is chosen so the peak current
in each inductor is:
I_IN(PK)
=
1
n
•
⎛
⎝⎜
1–
χ⎞
2 ⎠⎟
•
I_O(MAX)
1– D_MAX
=
1
2
•
⎛
⎝⎜
1+
0.4⎞
2 ⎠⎟
•
1–
5A
0.505
=
6.06A
32
5. The inductor ripple current is:
ΔI_L
=
χ
n
•
I_O(MAX)
1– D_MAX
=
0.4
2
• ^5A
1– 0.505
= 2.02A
6. The inductor value is therefore:
L
=
V_IN(MIN)
ΔI_L • f
• D_MAX
=
24V
2.02A • 300kHz
•
0.505
= 20μH
7. For a current limit value 30% higher than the maximum
load current:
I_O(CL) = 1.3 • I_O(MAX) = 1.3 • 5A = 6.5A
The saturation current rating of the inductors must
therefore exceed:
I_L(SAT)
≥
1
n
•
⎛
⎝⎜
1+
χ⎞
2 ⎠⎟
•
1.3 • I_O(MAX)
1– D_MAX
=
1
2
•
⎛
⎝⎜
1+
0.4⎞
2 ⎠⎟
•
1.3 • 5A
1– 0.505
=
7.9A
3862fb