參數(shù)資料
型號: LTC3534EDHC
廠商: LINEAR TECHNOLOGY CORP
元件分類: 穩(wěn)壓器
英文描述: SWITCHING REGULATOR, 1150 kHz SWITCHING FREQ-MAX, PDSO16
封裝: 5 X 3 MM, 0.75 MM HEIGHT, LEAD FREE, PLASTIC, MO-229WJED-1, DFN-16
文件頁數(shù): 5/20頁
文件大?。?/td> 218K
代理商: LTC3534EDHC
LTC3534
13
3534f
APPLICATIONS INFORMATION
Output Capacitor Selection
The bulk value of the output lter capacitor is set to reduce
the ripple due to charge into the capacitor each cycle. The
steady state ripple due to charge is given by:
ΔVP-PBoost =
IOUT VOUT –VIN(MIN)
()
COUT VOUT f
V
ΔVP-PBuck =
1
8L COUT f
2
VIN(MAX) –VOUT
()V
OUT
VIN(MAX)
V
where f = switching frequency in Hz, typically 1MHz.
COUT = output lter capacitor, F
IOUT = output load current, A
The output capacitance is usually many times larger than
the minimum value in order to handle the transient response
requirements of the converter. As a rule of thumb, the ratio
of the operating frequency to the unity-gain bandwidth of
the converter is the amount the output capacitance will
have to increase from the above calculations in order to
maintain the desired transient response. A 22μF or larger
ceramic capacitor is appropriate for most applications.
The other component of ripple is due to the ESR (equiva-
lent series resistance) of the output capacitor. Low ESR
capacitors should be used to minimize output voltage
ripple. For surface mount applications, Taiyo Yuden or
TDK ceramic capacitors, AVX TPS series tantalum capaci-
tors or Sanyo POSCAP are recommended. See Table 2 for
contact information.
Input Capacitor Selection
Since VIN is the supply voltage for the IC, as well as the
input to the power stage of the converter, it is recom-
mended to place at least a 10μF, low ESR ceramic bypass
capacitor close to the PVIN/VIN and PGND/GND pins. It is
also important to minimize any stray resistance from the
converter to the battery or other power source.
Optional Schottky Diodes
Schottky diodes across the synchronous switches B and
D are not required, but do provide a lower drop during the
break-before-make time (typically 15ns), thus improving
efciency. Use a surface mount Schottky diode such as an
MBRM120T3 or equivalent. Do not use ordinary rectier
diodes since their slow recovery times will compromise
efciency.
Output Voltage < 1.8V
The LTC3534 can operate as a buck converter with output
voltages as low as 400mV. Since synchronous switch D is
powered from VOUT and the RDS(ON) will increase signi-
cantly at output voltages below 1.8V typical, a Schottky
diode is required from SW2 to VOUT to provide the conduc-
tion path to the output at low VOUT voltages. The current
limit is folded back to 800mA when VOUT < 0.9V typical
which will signicantly reduce the output current capabil-
ity of the application. Note that Burst Mode operation is
inhibited at output voltages below 1.6V typical.
Closing the Feedback Loop
The LTC3534 incorporates voltage mode PWM control.
The control to output gain varies with operation region
(buck, boost, buck-boost), but is usually no greater than
15. The output lter exhibits a double pole response, as
given by:
fFILTER_POLE =
1
2
π L1COUT
Hz (in buck mode)
fFILTER_POLE =
VIN
2 VOUT π L1COUT
Hz (in boost mode)
where L1 is in Henries and COUT is in Farads.
Table 2. Capacitor Vendor Information
SUPPLIER PHONE
FAX
WEBSITE
AVX
(803) 448-9411 (803) 448-1943 www.avxcorp.com
Sanyo
(619) 661-6322 (619) 661-1055 www.sanyovideo.com
Taiyo
Yuden
(408) 573-4150 (408) 573-4159 www.t-yuden.com
TDK
(847) 803-6100 (847) 803-6296 www.component.tdk.com
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