參數(shù)資料
型號: LTC1871EMS-1
廠商: LINEAR TECHNOLOGY CORP
元件分類: 穩(wěn)壓器
英文描述: SWITCHING CONTROLLER, 1000 kHz SWITCHING FREQ-MAX, PDSO10
封裝: PLASTIC, MSOP-10
文件頁數(shù): 9/36頁
文件大?。?/td> 523K
代理商: LTC1871EMS-1
LTC1871-1
17
18711fb
APPLICATIONS INFORMATION
For many designs it is possible to choose a single capacitor
type that satises both the ESR and bulk C requirements
for the design. In certain demanding applications, however,
the ripple voltage can be improved signicantly by con-
necting two or more types of capacitors in parallel. For
example, using a low ESR ceramic capacitor can minimize
the ESR step, while an electrolytic capacitor can be used
to supply the required bulk C.
Once the output capacitor ESR and bulk capacitance have
been determined, the overall ripple voltage waveform
should be veried on a dedicated PC board (see Board
Layout section for more information on component place-
ment). Lab breadboards generally suffer from excessive
series inductance (due to inter-component wiring), and
these parasitics can make the switching waveforms look
signicantly worse than they would be on a properly
designed PC board.
The output capacitor in a boost regulator experiences high
RMS ripple currents, as shown in Figure 12. The RMS
output capacitor ripple current is:
IRMS(COUT) IO(MAX)
VO –VIN(MIN)
VIN(MIN)
Note that the ripple current ratings from capacitor manu-
facturers are often based on only 2000 hours of life. This
makes it advisable to further derate the capacitor or to
choose a capacitor rated at a higher temperature than
required. Several capacitors may also be placed in parallel
to meet size or height requirements in the design.
Manufacturers such as Nichicon, United Chemicon and
Sanyo should be considered for high performance through-
hole capacitors. The OS-CON semiconductor dielectric
capacitor available from Sanyo has the lowest product of
ESR and size of any aluminum electrolytic, at a somewhat
higher price.
In surface mount applications, multiple capacitors may
have to be placed in parallel in order to meet the ESR or
RMS current handling requirements of the application.
Aluminum electrolytic and dry tantalum capacitors are
both available in surface mount packages. In the case of
tantalum, it is critical that the capacitors have been surge
tested for use in switching power supplies. An excellent
choice is AVX TPS series of surface mount tantalum. Also,
ceramic capacitors are now available with extremely low
ESR, ESL and high ripple current ratings.
Boost Converter: Input Capacitor Selection
The input capacitor of a boost converter is less critical
than the output capacitor, due to the fact that the inductor
is in series with the input and the input current waveform
is continuous (see Figure 12b). The input voltage source
impedance determines the size of the input capacitor,
VIN
LD
SW
12a. Circuit Diagram
12b. Inductor and Input Currents
COUT
VOUT
RL
IIN
IL
12c. Switch Current
ISW
tON
12d. Diode and Output Currents
12e. Output Voltage Ripple Waveform
IO
ID
VOUT
(AC)
tOFF
ΔVESR
RINGING DUE TO
TOTAL INDUCTANCE
(BOARD + CAP)
ΔVCOUT
Figure 12. Switching Waveforms for a Boost Converter
相關PDF資料
PDF描述
LTC1871IMS-1#TR SWITCHING CONTROLLER, 1000 kHz SWITCHING FREQ-MAX, PDSO10
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