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參數(shù)資料
| 型號： | 48S15.10000TC |
| 英文描述： | SMPS Controller |
| 中文描述： | 開關電源控制器 |
| 文件頁數(shù)： | 4/6頁 |
| 文件大小： | 120K |
| 代理商： | 48S15.10000TC |
15 Watt TC Single Series DC/DC Converters
2401 Stanwell Drive Concord, California 94520 Ph: 925/687-4411 or 800/542-3355 Fax: 925/687-3333 www.calex.com Email: sales@calex.com
4
3/2001
Solution
According to the 15 Watt TC Single Series
“
Reflected Input
Ripple vs. Line Input
”
curve at 40 VDC input and 2.25 Amps
output (75% of rated load), the reflected input ripple can be
read as 650 mA RMS. From the derating guidelines the
capacitor
’
s rated voltage and ripple current can be determined.
Capacitor voltage rating is calculated as:
1
A capacitor selection can now be made. Look only at
controlled low ESR types (where the ESR is specified as a
maximum) because these usually have the highest ripple
current capability per unit volume.
Be careful to compare apples to apples. Some
manufacturers specify their capacitors at 85
°
C and others
specify at 105
°
C. The manufacturers give temperature derating
guidelines, so all capacitors should be normalized to your
maximum ambient (plus 5
°
C to account for self heating)
before making a selection. Since the 15 Watt TC Single Series
operates at 120 kHz the frequency usually does not have to
be derated since most modern low ESR capacitors are rated
at 100 kHz.
One note: The temperature derating multipliers are based
on the capacitor
’
s expected life at 105
°
C. The life of a
capacitor operating at a significantly lower temperature will
not be greater if the ripple current in the part is increased over
the 105
°
C rating. This means that a capacitor rated for 1 A
RMS current at 105
°
C and 2 A RMS at 50
°
C will have the same
life if used at either point while the same capacitor used at 1
A RMS and 50
°
C will have a longer life.
Suggested Capacitor Sources
Suitable capacitors can be acquired from the following sources:
United Chemi-Con
SXE, RXC, RZ and RZA Series
Suggested Part:
SXE100VB221M12.5X35LL
220μF, 100V, 105
°
C Rated
ESR=0.087 ohms
Allowable Ripple=1.45 A @ 105
°
C
Nichicon
PR and PF
Suggested Part:
UPR2A102MPH
1000μF, 100V, 105
°
C Rated
ESR=0.047 ohms
Allowable Ripple=1.32 A @ 105
°
C
Sizing The Input Capacitor
For maximum reliability the TC Single Series must use a
capacitor of sufficient ripple handling capability connected
across the input pins. The probable result of undersizing (over
stressing) this capacitor is increased self heating, shortening
of the capacitors and hence shortening of your systems
’
life.
Oversizing the capacitor can have a negative effect on your
product
’
s cost and size, although this kind of overdesign does
not result in shorter life of any components. There is no one
optimum value for this capacitor. The size and capacity are
dependent on the following factors:
1) expected ambient temperature and your temperature
derating guidelines
2) your ripple current derating guidelines
3) the maximum load expected on the converter
4) the minimum input voltage expected on the converter
5) the statistical probability that your system will spend a
significant amount of time at any worst case extreme
Factors 1 and 2 are determined by your system design
guidelines. These can range from 50% to 100% of the
manufacturer
’
s rated maximum, although a usual derating
factor is 70% of manufacturer
’
s maximum limit. 70% derating
means that if the capacitor manufacturer says their capacitor
can do 1 A RMS and 100 VDC you would not use the part over
700 mA RMS and 70 VDC. Surge voltage rating should also
be evaluated against any expected voltage surges when
selecting a capacitor working voltage.
Factors 3 and 4 realistically determine the worst case ripple
current. The reflected ripple current increases with output
load and increases as the input voltage decreases. So if you
are running with a solid 48 VDC input and at 50% load your
capacitors required ripple current rating would decrease by
more than 2:1 from what would be required for operation at 20
VDC with full load (see the
“
Input Reflected Ripple
”
curve).
Factor 5 is not easy to quantify. At CALEX, we can make
no assumptions about a customer
’
s system so we design for
continuous operation at worst case extremes.
Example Of Capacitor Sizing
Given the following conditions, select the minimum size
capacitor needed to provide reliable performance:
Converter ......................................... 48S5.3000TC
Minimum Input Voltage.................... 40 VDC
Maximum Input Voltage................... 52 VDC
Maximum Load ................................ 2.25 Amps
Maximum Ambient Temperature ..... 40
°
C
Your Capacitor Voltage
Derating Guideline ........................... 70% of Maximum
Specification
Your Capacitor Current
Derating Guideline ........................... 70% of Maximum
Specification
Voltage Derating Factor
x Maximum Expected Input
V = 0.7
I =
1
x Reflected Ripple
Current Derating Factor
= 0.7
x 650 mA = 0.93 A RMS or greater at 45
°
C
(40
°
C ambient + 5
°
C for self heating)
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