參數(shù)資料
型號: LTC3879EUD#TRPBF
廠商: LINEAR TECHNOLOGY CORP
元件分類: 穩(wěn)壓器
英文描述: SWITCHING CONTROLLER, PQCC16
封裝: 3 X 3 MM, LEAD FREE, PLASTIC, MO-220WEED-4, QFN-16
文件頁數(shù): 13/28頁
文件大?。?/td> 302K
代理商: LTC3879EUD#TRPBF
LTC3879
20
3879f
at 25°C) is required to account for variation in MOSFET
on-resistance with temperature. Choosing an RJK0330
(RDS(ON) = 2.8mΩ (nominal) 3.9mΩ (maximum), VGS =
4.5V,
θJA = 40°C/W) yields a drain source voltage of:
VI
I
m
DS
LIMIT
RIPPLE
=
()
()
–.
1
2
39
Ωρτ
VRNG sets current limit by xing the maximum peak VDS
voltage on the bottom MOSFET switch. As a result, the
average DC current limit includes signicant temperature
and component variability. Design to guarantee that the
average DC current limit will always exceed the rated oper-
ating output current by assuming worst-case component
tolerance and temperature.
The worst-case minimum INTVCC is 5.15V. The bottom
MOSFET worst-case RDS(ON) is 3.9mΩ and the junction
temperature is 80°C above a 70°C ambient with
ρ150°C =
1.5. Set TON equal to the minimum specication of 15%
low and the inductor 15% high.
By setting ILIMIT equal to 15A we get 79mV for peak VDS
voltage which corresponds to a VRNG equal to 592mV:
VA
A
m
V
DS =
15
1
2
51
0 85
115
39
515
53
– .
.
Ω
V
VV
RNG
DS
.
15
75
=
Verify that the calculated nominal TJ is less than the
assumed worst-case TJ in the bottom MOSFET:
P
VV
V
Am
W
T
BOT
J
=
()
=
28
12
28
15
15 39
125
70
2
–.
. .
.
Ω
°°+
°
=
°
CW
C W
C
1 25
40
120
.
/
Because the top MOSFET is on for a short time, an
RJK0305DPB (RDS(ON) = 10mΩ (nominal) 13mΩ (maxi-
mum), CMILLER = QGD/10V = 150pF, VBOOST = 5V, VGS =
4.5V, VMILLER=3V,θJA=40°C/W)issufcient.Checkingits
power dissipation at current limit with =
ρ100°C = 1.4:
P
V
Am
V
A
TOP =
()
+
()
12
28
15
1 4 13
28
15
2
22
.
.
Ω
()
+
=
150
25
53
12
3
400
018
pF
VV
V
kHz
W
.
.
ΩΩ
++=
=° +
°
=
°
058
076
70
0 76
40
100
..
./
WW
TCW
C W
C
J
The junction temperatures will be signicantly less at
nominal current, but this analysis shows that careful
attention to heat sinking will be necessary.
Select CIN to give an RMS current rating greater than 4A
at 85°C. The output capacitor COUT1 is chosen for a low
ESR of 4.5mΩ to minimize output voltage changes due to
APPLICATIONS INFORMATION
Figure 10. Design Example: 1.2V/15A at 400kHz
+
TRACK/SS
LTC3879
BOOST
16
CB
0.22μF
M1
RJK0305DPB
CVCC
4.7μF
CC1
220pF
CC2
33pF
DB
CMDSH-3
L1
0.56μH
COUT1
330μF
2.5V
2
COUT2
47μF
6.3V
2
+
CIN1
10μF
50V
3
CIN2
100μF
50V
VOUT
1.2V
15A
3879 F10
VIN
4.5V TO 28V
1
PGOOD
RPG
100k
R2
80.6k
RC
27k
RFB1
10.0k
R1
10.0k
TG
15
2
VRNG
SW
14
3
MODE
PGND
13
4
ITH
BG
12
5
SGND
INVCC
11
6
ION
VIN
10
7
VFB
RUN
9
8
RON
432k
RFB2
10.0k
M2
RJK0330DPB
CIN1: UMK325BJ106MM 3
COUT1: SANYO 2R5TPE330M9 2
COUT2: MURATA GRM31CR60J476M 2
L1: VISHAY IHLP4040DZ-11 0.56μH
CSS
0.1μF
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PDF描述
LTC3879IUD#PBF SWITCHING CONTROLLER, PQCC16
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