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参数资料
| 型号： | ADP3170JRU-REEL |
| 厂商： | ANALOG DEVICES INC |
| 元件分类： | 稳压器 |
| 英文描述： | SWITCHING CONTROLLER, PDSO20 |
| 封装： | TSSOP-20 |
| 文件页数： | 4/16页 |
| 文件大小： | 177K |
| 代理商： | ADP3170JRU-REEL |
REV. 0
ADP3170
–12–
higher efficiency, but increase the system cost. A Fairchild
FDB7045L (RDS(ON) = 4.5 m nominal, 6 m worst-case) is a
good choice for both the low-side and high-side MOSFET.
With this choice, the high-side MOSFET dissipation is:
PR
I
VI
Q
f
I
VQ
f
Pm
A
nC
kHz
A
V
nC
kHz
W
HSF
DS ON HSF
HSF MAX
IN
L PEAK
G
MIN
G
IN
RR
MIN
HSF
=×
+
××
×
+
××
=×
+
××
×
+
××
=
()
(
)
()
.
2
614 7
5
28 6
50
183
21
5
100
183
2 04
(24)
where the second term represents the turn-off loss of the
MOSFET and the third term represents the turn-on loss due to
the stored charge in the body diode of the low-side MOSFET.
In the second term, QG is the gate charge to be removed from
the gate for turnoff and IG is the gate turn-off current. From the
data sheet, the value of QG for the FDB7045L is 50 nC and the
peak gate drive current provided by the ADP3170 is about 1 A. In
the third term, QRR is the charge stored in the body diode of
the low-side MOSFET at the valley of the inductor current.
The data sheet of the FDB7045L does not give that informa-
tion, so an estimated value of 100 nC is used. The estimate is
based on information found on the data sheets of similar devices.
The low-side MOSFET dissipation is:
PR
I
Pm
A
W
LSF
DS ON HSF
HSF MAX
LSF
=×
=
()
(
)
.
2
618
1 94
(25)
Note that there are no switching losses in the low-side MOSFET.
Surface mount MOSFETs are preferred in CPU core converter
applications due to their ability to be handled by automatic
assembly equipment. The TO-263 package offers the power
handling of a TO-220 in a surface mount package. However,
this package still needs adequate copper area on the PCB to
help move the heat away from the package.
The junction temperature for a given area of two-ounce copper
can be approximated using:
TP
T
AD
A
JJ
=×
() +
θ
(26)
assuming:
JA = 45°C/W for 0.5 in
2
JA = 36°C/W for 1 in
2
JA = 28°C/W for 2 in
2
For 1 in2 of copper area attached to each transistor and an
ambient temperature of 50
°C:
TC W
W
C
TC W
W
C
HSF
LSF
J
=×
() +=
=×
() +=
28
2 06
50
108
28
1 94
50
104
oo
o
oo
o
/.
All of the above-calculated junction temperatures are safely
below the 175
°C maximum specified junction temperature of
the selected MOSFETs.
Power MOSFETs
Two external N-channel power MOSFETs must be selected for
use with the ADP3170, one for the main switch and one for the
synchronous switch. The main selection parameters for the power
MOSFETs are the threshold voltage (VGS(TH)), the ON-resistance
(RDS(ON)), and the gate charge (QG). Logic-level MOSFETs are
highly recommended. Only logic-level MOSFETs with VGS ratings
higher than the absolute maximum value of VCC should be used.
The maximum output current IO(MAX) determines the RDS(ON)
requirement for the two power MOSFETs. When the ADP3170
is operating in continuous mode, the simplifying assumption can
be made that one of the two MOSFETs is always conducting
the average load current. For VIN = 5 V and VOUT = 1.8 V, the
maximum duty ratio of the high-side FET is:
Df
t
DkHz
s
HSF MAX
MIN
OFF
HSF MAX
()
–
–(
.
)
%
=×
()
=×
=
1
1183
3 3
40
(17)
The maximum duty ratio of the low-side (synchronous rectifier)
MOSFET is:
DD
LSF MAX
HSF MAX
()
–%
==
160
(18)
The maximum rms current of the high-side MOSFET is:
ID
II
I
vI
I
AA
A
HSF MAX
L VALLEY
L PEAK
HSF MAX
()
(
)
(
)
()
.
.(
.
)
.
=×
+×
() +
=×
+×
+
=
22
3
04
17 4
28 6
3
14 7
(19)
The maximum rms current of the low-side MOSFET is:
ID
II
I
AA
A
LSF MAX
L VALLEY
L PEAK
HSF MAX
()
(
)
(
)
()
.
..
.
=×
+×
()+
=×
+×
()+
=
22
3
06
17 4
28 6
3
18
(20)
The RDS(ON) for each MOSFET can be derived from the
allowable dissipation. If 10% of the maximum output power is
allowed for MOSFET dissipation, the total dissipation will be:
PV
I
PV
A
W
D FET
OUT
OUT MAX
D FET
s
()
(
)
()
.
..
.
=×
×
=×
×
=
01
01 18
23
41
(21)
Allocating half of the total dissipation for the high-side MOSFET and
half for the low-side MOSFET, and assuming that the resis-
tive loss of the high-side MOSFET is one-third, and the switching
loss is two-thirds of its portion, the required maximum MOSFET
resistances will be:
R
P
I
W
A
m
DS ON HSF
D FETS
HSF MAX
()
.
=
×
=
×
=
3
41
314 7
6
2
(22)
R
P
I
W
A
m
DS ON LS
D FETS
LSF MAX
()
.
==
×
=
22
41
218
6
(23)
Note that there is a trade-off between converter efficiency and
cost. Larger MOSFETs reduce the conduction losses and allow
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相关代理商/技术参数 |
参数描述 |
|---|---|
| ADP3170JRU-REEL7 | 制造商:Analog Devices 功能描述: |
| ADP3170JRUZ-R7 | 制造商:Rochester Electronics LLC 功能描述: 制造商:Analog Devices 功能描述: |
| ADP3170JRUZ-REEL7 | 功能描述:IC CTRLR VRM 8.5 W/REG 20TSSOP RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - 专用型 系列:- 产品培训模块:Lead (SnPb) Finish for COTS Obsolescence Mitigation Program 标准包装:2,000 系列:- 应用:电源，ICERA E400，E450 输入电压:4.1 V ~ 5.5 V 输出数:10 输出电压:可编程 工作温度:-40°C ~ 85°C 安装类型:表面贴装 封装/外壳:42-WFBGA，WLCSP 供应商设备封装:42-WLP 包装:带卷 (TR) |
| ADP3171 | 制造商:AD 制造商全称:Analog Devices 功能描述:Synchronous Buck Controller with Dual Linear Regulator Controllers |
| ADP3171JR | 制造商:Rochester Electronics LLC 功能描述:1.2V VTT BUCK CNTRLR W/2 LDOS & PWR GOOD - Bulk |
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