参数资料
型号: LTC3865IUH#PBF
厂商: LINEAR TECHNOLOGY CORP
元件分类: 稳压器
英文描述: DUAL SWITCHING CONTROLLER, 880 kHz SWITCHING FREQ-MAX, PQCC32
封装: 5 X 5 MM, LEAD FREE, PLASTIC, MO-220WHHD, QFN-32
文件页数: 26/38页
文件大小: 400K
代理商: LTC3865IUH#PBF
LTC3865/LTC3865-1
32
3865fb
APPLICATIONS INFORMATION
With ILIM oating, the equivalent RSENSE resistor value
can be calculated by using the minimum value for the
maximum current sense threshold (44mV).
R
V
I
SENSE EQUIV
SENSE MIN
LOAD MAX
L NOM
()
(
=
+
Δ
))
.
2
44
5
15
2
77
=
+
mV
A
m
Ω
The equivalent RSENSE is the same for Channel 2.
The Coiltronics (Cooper) HCP0703-2R2 (20mΩ DCRMAX
at 20°C) and HCP0703-3R3 (30mΩ DCRMAX at 20°C) are
chosen. At 100°C, the estimated maximum DCR values are
26.4mΩ and 39.6mΩ. The divider ratios are:
R
DCR
at T
m
D
SENSE EQUIV
MAX
L MAX
==
()
.
77
26 4
Ω
==
03
77
39 6
02
.;
.
and
m
Ω
For each channel, 0.1μF is selected for C1.
RR
L
DCR
at
C C
H
mF
MAX
12
20
1
22
20
0 1
1
||
()
.
=
°
=
μ
Ω
..
;
.
1
33
30
0 1
11
kand
H
mF
k
μ
Ω
=
For channel 1, the DCRSENSE lter/divider values are:
R
RR
R
k
R
RR
R
k
D
1
12
11
02
55
2
1
55
==
=
=
||
.
.;
.
0
02
10 2
137
.
k
The power loss in R1 at the maximum input voltage is:
PR
VV
V
R
VV
LOSS
IN MAX
OUT
1
20
3 3
3
=
=
()
(.
)
()
..
.
3
55
10
V
k
mW
=
The respective values for Channel 2 are R1 = 3.66k,
R2 = 1.57k; and PLOSS R1 = 8mW.
Burst Mode operation is chosen for high light load efciency
(Figure 15) by oating the MODE/PLLIN pin. Power loss
due to the DCR sensing network is slightly higher at light
loads than would have been the case with a suitable sense
resistor (8mΩ). At heavier loads, DCR sensing provides
higher efciency.
The power dissipation on the topside MOSFET can be easily
estimated. Choosing a Siliconix Si4816BDY dual MOSFET
results in: RDS(ON) = 0.023Ω/0.016Ω, CMILLER 100pF.
At maximum input voltage with T(estimated) = 50°C:
P
V
CC
MAIN =
()
°
[]
33
20
5
1
0 005 50
25
00
2
.
(.
)(
)
. 2
23
20
5
2
100
1
52 3
1
2
Ω
()+()
Ω
()(
)
+
V
A
pF
–.
..3
500
186
()=
kHz
mW
LOAD CURRENT (mA)
0.01
70
EFFICIENCY
(%)
POWER
LOSS
(mW)
80
90
0.1
1
10
60
50
40
100
0.1
1
0.01
10
3865 F16
DCR
8mΩ
POWER LOSS
EFFICIENCY
Figure 15. Design Example Efciency vs Load
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