ltc3853euj Linear Technology Corporation, ltc3853euj Datasheet - Page 29

• Manufacturer Part Number: ltc3853euj
• Description: Triple Output, Multiphase Synchronous Step-down Controller
• Manufacturer: Linear Technology Corporation

APPLICATIONS INFORMATION
standard values are 3.3μH, 3.3μH and 1.5μH. At the
maximum input voltage (20V), the ripple will be:
Channel 1 will have ~2.3A (46%) ripple, and both channel
2 and channel 3 will have ~1.75A (35%) ripple. The peak
inductor current will be the maximum DC value plus one-
half the ripple current, or 6.15A for channel 1 and 5.88A
for channels 2 and 3.
With I
calculated by using the minimum value for the maximum
current sense threshold (65mV).
V
OUT1
R
ΔI
5V
5A
SENSE EQUIV
L MAX
LIM
+
(
M1, M2, M3: Si4816BDY
CHANNEL 1: R
CHANNEL 2: R
CHANNEL 3: R
FOR CHANNEL 3, 0.068μF WAS SUBSTITUTED FOR 0.1μF AND 2.43k WAS SUBSTITUTED
FOR 2.21k TO MEET MINIMUM 15mV RIPPLE AT SENSE INPUT REQUIREMENT
high, the equivalent R
330μF
10V
3.3μH
105k
10pF
1%
1430Ω
(
4.75k
)
=
V
C
ITH1
ITH2
ITH3
20k
1%
f
P1,2,3
OUT
)
M1
•
= 15k, C
= 18k, C
= 10k, C
=
=
L
1 2
I
⎛
⎜
⎝
LOAD MAX
. •
0.1μF
ITH1
ITH2
ITH3
1
−
= 1.5nF, C
= 1.5nF, C
= 1.5nF, C
R
⎛
⎝ ⎜
ITH1,2,3
C
(
V
V
ITH1,2,3
5
IN MAX
SENSE MIN
V
A
65
Figure 13. High Effi ciency Triple 5V/3.3V/1.2V Step-Down Converter
OUT
(
P1
P2
P3
SENSE
+
)
mV
= 220pF
= 220pF
= 330pF
4.7μF
+
Δ
(
I
)
Δ
L MAX
⎞
⎟
⎠
TG1
PGOOD12
PGOOD3
SW1
BG1
MODE/PLLIN
ILIM
SENSE1
SENSE1
V
I
V
SGND
EXTV
resistor value can be
(
TH1,2,3
I
FB1
FB3
2
L NOM
V
)
(
IN
CC
2
+
–
TK/SS1,2,3
DRV
LTC3853
)
⎞
⎠ ⎟
FREQ/PLLFLTR
CC12
) )
BOOST1,2,3
≅
C
0.1μF
RUN1,2,3
INTV
SENSE2
SENSE2
SENSE3
SENSE3
SS1,2,3
9
PGND
m
SW2
V
SW3
CC
BG2
BG3
TG2
TG3
FB2
Ω
+
–
+
–
C
B1,2,3
D
3.16k
B1,2,3
10k
0.1μF
SW1,2,3
The 1.2 factor adds margin for component variation and
overcurrent headroom during full load transients.
The equivalent R
and 3.
The Vishay IHLP2525CZER3R3M01 (30mΩ DCR
20°C) and IHLP2525CZER1R5M01 (15mΩ DCR
20°C,) are chosen. At 100°C, the estimated maximum DCR
values are 39.6mV and 19.8mV. The divider ratios are:
For each channel, 0.1μF is selected for C1.
INTV
R
CC
R
1nF
1
D
||
=
R
2
and
DCR
M2
=
=
20k
1%
63.4k
R
1%
(
1
DCR
SENSE EQUIV
19 8
MAX
1 1 00
4.75k
9
1430Ω
3.3μH
0.1μF
10pF
.
m
SENSE
MAX
Ω
m
at T
Ω
(
Ω
+
and
L MAX
330μF
6V
at
L
(
V
3.3V
5A
≅
OUT2
is the same for channels 1, 2
0 45
20
)
15
.
)
°
m
C C
=
1 5
) •
Ω
.
39 6
• .
μ
9
1
0 1
.
m
H
M3
3853 F13
=
m
Ω
μ
30
LTC3853
Ω
F
2.43k
20k
1%
m
=
0.068μF
=
1.5μH
1.82k
3 3
22μF
50V
10k
1%
Ω
1000
0
.
V
7V TO 20V
. .
IN
• .
μ
23
+
0 1
H
29
MAX
MAX
;
330μF
6V
Ω
V
1.2V
5A
μ
OUT3
F
3853f
at
at