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| 型號(hào)： | DCP022415 |
| 廠商： | Texas Instruments, Inc. |
| 英文描述： | Miniature, 2W, Isolated UNREGULATED DC/DC CONVERTERS(微型，2W，隔離未穩(wěn)壓DC/DC轉(zhuǎn)換器) |
| 中文描述： | 微型，中，2W，隔離未穩(wěn)壓DC / DC轉(zhuǎn)換器（微型，中，2W，隔離未穩(wěn)壓直流/直流轉(zhuǎn)換器） |
| 文件頁(yè)數(shù)： | 9/17頁(yè) |
| 文件大小： | 483K |
| 代理商： | DCP022415 |
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Decoupling Ceramic Capacitors
Input Capacitor and the Effects of ESR
0
f
O
Frequency
X
L
Z
Where:
X is the reactance due to the capacitance.
X is the reactance due to the ESL.
f is the resonant frequency.
Z =
(X
X )
L
-
C
2
2
+ (ESR)
Output Ripple Calculation Example
SBVS011E–MARCH 2000–REVISED AUGUST 2006All capacitors have losses because of internal
equivalent series resistance (ESR), and to a lesser
degree, equivalent series inductance (ESL). Values
for ESL are not always easy to obtain. However,
some manufacturers provide graphs of frequency
versus capacitor impedance. These graphs typically
show the capacitor impedance falling as frequency is
increased (as shown in
Figure 10
). As the frequency
is increases, the impedance stops decreasing and
begins to rise. The point of minimum impedance
indicates the resonant frequency of the capacitor.
This
frequency
is
where
capacitance and inductance reactance are of equal
magnitude. Beyond this point, the capacitor is not
effective as a capacitor.
If the input decoupling capacitor is not ceramic with
< 20m
ESR,
then
at
transistors switch on, the voltage at the input pins
falls momentarily. Should the voltage fall below
approximately 4V, the DCP detects an under-voltage
condition and switches the DCP drive circuits to the
off state. This detection is carried out as a precaution
against a genuine low input voltage condition that
could slow down or even stop the internal circuits
from operating correctly. A slow-down or stoppage
would result in the drive transistors being turned on
too long, causing saturation of the transformer and
destruction of the device.
the
instant
the
power
the
components
of
Following detection of a low input voltage condition,
the device switches off the internal drive circuits until
device tries to restart. If the input capacitor is still
unable to maintain the input voltage, shutdown
recurs. This process is repeated until the capacitor is
charged sufficiently to start the device correctly.
Otherwise, the device will be caught up in a loop.
Normal startup should occur in approximately 1ms
from power being applied to the device. If a
considerably
longer
startup
encountered, it is likely that either (or both) the input
supply
or
the
capacitors
adequately.
For 5V to 15V input devices, a 2.2
μ
F low-ESR
ceramic
capacitor
ensures
performance. For the remaining input voltage ranges,
0.47
μ
F
ceramic
capacitors
Tantalum capacitors are not recommended, since
most do not have low-ESR values and will degrade
performance. If tantalum capacitors must be used,
close attention must be paid to both the ESR and
voltage as derated by the vendor.
duration
time
is
are
not
performing
a
good
startup
Figure 10. Capacitor Impedance vs Frequency
are
recommended.
At f
O
, X
C
= X
L
; however, there is a 180
°
phase
difference resulting in cancellation of the imaginary
component.
The
resulting
impedance at the resonant point is the real part of
the complex impedance; namely, the value of the
ESR. The resonant frequency must be well above
the 800kHz switching frequency of the DCP and
DCVs.
effect
is
that
the
DCP020505: Output voltage 5V, Output current 0.4A.
At full output power, the load resistor is 12.5
.
Output capacitor of 1
μ
F, ESR of 0.1
. Capacitor
discharge time 1% of 800kHz (ripple frequency):
t
DIS
= 0.0125
μ
s
t = C
×
R
LOAD
t = 1
×
10
-6
×
12.5 = 12.5
μ
s
V
DIS
= V
O
(1 – EXP(–t
DIS
/
τ
))
V
DIS
= 5mV
By contrast, te voltage dropped because of ESR:
V
ESR
= I
LOAD
×
ESR
V
ESR
= 40mV
Ripple voltage = 45mV
The effect of the ESR is to cause a voltage drop
within the capacitor. The value of this voltage drop is
simply the product of the ESR and the transient load
current, as shown:
V
IN
= V
PK
– (ESR
×
I
TR
)
Where:
V
IN
is the voltage at the device input.
V
PK
is the maximum value of the voltage on the
capacitor during charge.
I
TR
is the transient load current.
The other factor that affects the performance is the
value of the capacitance. However, for the input and
the full wave outputs (single-output voltage devices),
ESR is the dominant factor.
9
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| DCP022415DP | 制造商:Texas Instruments 功能描述:1C ISOLATED DC/DC CONVERTER 14-DIP |
| DCP022415DU | 功能描述:DC/DC轉(zhuǎn)換器 Mini 2W Iso Unreg DC/DC Converter RoHS:否 制造商:Murata 產(chǎn)品: 輸出功率: 輸入電壓范圍:3.6 V to 5.5 V 輸入電壓（標(biāo)稱）: 輸出端數(shù)量:1 輸出電壓（通道 1）:3.3 V 輸出電流（通道 1）:600 mA 輸出電壓（通道 2）: 輸出電流（通道 2）: 安裝風(fēng)格:SMD/SMT 封裝 / 箱體尺寸: |
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