数据搜索系统，热门电子元器件搜索
  Chinese  ▼
ALLDATASHEETCN.COM

X  

预览 PDF HTML

SC1485ITSTRT 数据表(PDF) 13 Page - Semtech Corporation

部件名 SC1485ITSTRT
功能描述  Dual Synchronous Buck Pseudo Fixed Frequency Power Supply Controller
PDF  27 Pages
Scroll/Zoom Zoom In 100%  Zoom Out
制造商  SEMTECH [Semtech Corporation]
网页  http://www.semtech.com
标志 SEMTECH - Semtech Corporation

SC1485ITSTRT 数据表(HTML) 13 Page - Semtech Corporation

Back Button SC1485ITSTRT Datasheet HTML 9Page - Semtech Corporation SC1485ITSTRT Datasheet HTML 10Page - Semtech Corporation SC1485ITSTRT Datasheet HTML 11Page - Semtech Corporation SC1485ITSTRT Datasheet HTML 12Page - Semtech Corporation SC1485ITSTRT Datasheet HTML 13Page - Semtech Corporation SC1485ITSTRT Datasheet HTML 14Page - Semtech Corporation SC1485ITSTRT Datasheet HTML 15Page - Semtech Corporation SC1485ITSTRT Datasheet HTML 16Page - Semtech Corporation SC1485ITSTRT Datasheet HTML 17Page - Semtech Corporation Next Button
Zoom Inzoom in Zoom Outzoom out
 13 / 27 page
background image
13
 2005 Semtech Corp.
www.semtech.com
SC1485
POWER MANAGEMENT
We will select a value of 12.5m
Ω maximum for our
design, which would be achieved by using two 25m
Ω
output capacitors in parallel. Note that for constant-on
converters there is a minimum ESR requirement for
stability which can be calculated as follows:
SW
OUT
)
MIN
(
ESR
f
C
2
3
R
•
•
π
•
=
This criteria should be checked once the output
capacitance has been determined.
Now that we know the output ESR we can calculate the
output ripple voltage:
P
P
)
MAX
(
VBAT
_
RIPPLE
ESR
)
MAX
(
VBAT
_
RIPPLE
V
I
R
V
−
•
=
and
P
P
)
MIN
(
VBAT
_
RIPPLE
ESR
)
MIN
(
VBAT
_
RIPPLE
V
I
R
V
−
•
=
For our example:
V
RIPPLE_VBAT(MAX) = 27mVP-P and VRIPPLE_VBAT(MIN) = 22mVP-P
Note that in order for the device to regulate in a
controlled manner, the ripple content at the feedback
pin, V
FB, should be approximately 15mVP-P at minimum
V
BAT, and wo rst case no smaller than 10mVP-P. If
V
RIPPLE_VBAT(MIN) is less than 15mVP-P the above component
values should be revisited in order to improve this. Quite
often a small capacitor, C
TOP, is required in parallel with
the top feedback resistor, R
TOP, in order to ensure that
V
FB is large enough. CTOP should not be greater than
100pF. The value of C
TOP can be calculated as follows,
where R
BOT is the bottom feedback resistor. Firstly
calculating the value of Z
TOP required:
()Ohms
015
.
0
V
015
.
0
R
Z
)
MIN
(
VBAT
_
RIPPLE
BOT
TOP
−
•
=
Secondly calculating the value of C
TOP required to achieve
this:
F
f
2
R
1
Z
1
C
)
MIN
(
VBAT
_
SW
TOP
TOP
TOP
•
π
•


−
=
For our example we will use R
TOP = 20.0k Ω and
R
BOT = 14.3kΩ, therefore:
Z
TOP = 6.67kΩ and CTOP = 60pF
We will select a value of C
TOP = 56pF. Calculating the
value of V
FB based upon the selected CTOP:
P
P
TOP
)
MIN
(
VBAT
_
SW
TOp
BOT
BOT
)
MIN
(
VBAT
_
RIPPLE
)
MIN
(
VBAT
_
FB
V
C
f
2
R
1
1
R
R
V
V
−
•
•
π
•
+
+
•
=
For our example:
V
FB_VBAT(MIN) = 14.8mVP-P - good
Next we need to calculate the minimum output
capacitance required to ensure that the output voltage
does not exceed the transient maximum limit, POSLIM
TR,
starting from the actual static maximum, V
OUT_ST_POS, when
a load release occurs:
V
ERR
V
V
DC
OUT
POS
_
ST
_
OUT
+
=
For our example:
V
OUT_ST_POS = 1.224V
V
TOL
V
POSLIM
TR
OUT
TR
•
=
Where TOL
TR is the transient tolerance. For our example:
POSLIM
TR = 1.296V
The minimum output capacitance is calculated as
follows:
()F
V
POSLIM
2
I
I
L
C
2
POS
_
ST
_
OUT
2
TR
2
)
MAX
(
VBAT
_
RIPPLE
OUT
)
MIN
(
OUT
−


+
•
=
This calculation assumes the absolute worst case
condition of a full-load to no load step transient occurring
when the inductor current is at its highest. The
capacitance required for smaller transient steps my be
calculated by substituting the desired current for the I
OUT
term.



Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27


数据表 下载

Go To PDF Page


链接网址



ALLDATASHEET是否为您带来帮助?  [ DONATE ] 

关于 Alldatasheet   |   广告服务   |   联系我们   |   隐私政策   |   数据表链接    |   链接交换   |   制造商名单
All Rights Reserved©Alldatasheet.com


Mirror Sites
English : Alldatasheet.com  |   English : Alldatasheet.net  |   Chinese : Alldatasheetcn.com  |   German : Alldatasheetde.com  |   Japanese : Alldatasheet.jp
Russian : Alldatasheetru.com  |   Korean : Alldatasheet.co.kr  |   Spanish : Alldatasheet.es  |   French : Alldatasheet.fr  |   Italian : Alldatasheetit.com
Portuguese : Alldatasheetpt.com  |   Polish : Alldatasheet.pl  |   Vietnamese : Alldatasheet.vn
Indian : Alldatasheet.in  |   Mexican : Alldatasheet.com.mx  |   British : Alldatasheet.co.uk  |   New Zealand : Alldatasheet.co.nz
Family Site : ic2ic.com  |   icmetro.com