参数资料
型号: LT3757HMSE#TRPBF
厂商: LINEAR TECHNOLOGY CORP
元件分类: 稳压器
英文描述: SWITCHING REGULATOR, 1000 kHz SWITCHING FREQ-MAX, PDSO10
封装: 3 X 3 MM, LEAD FREE, PLASTIC, MSOP-10
文件页数: 8/36页
文件大小: 436K
代理商: LT3757HMSE#TRPBF
LT3757
16
3757fc
applicaTions inForMaTion
Figure 6. The Output Ripple Waveform of a Boost Converter
VOUT
(AC)
tON
VESR
RINGING DUE TO
TOTAL INDUCTANCE
(BOARD + CAP)
VCOUT
3757 F05
tOFF
TJ must not exceed the MOSFET maximum junction
temperature rating. It is recommended to measure the
MOSFETtemperatureinsteadystatetoensurethatabsolute
maximum ratings are not exceeded.
Boost Converter: Output Diode Selection
To maximize efficiency, a fast switching diode with low
forward drop and low reverse leakage is desirable. The
peak reverse voltage that the diode must withstand is
equal to the regulator output voltage plus any additional
ringing across its anode-to-cathode during the on-time.
The average forward current in normal operation is equal
to the output current, and the peak current is equal to:
ID(PEAK) =IL(PEAK) = 1+
χ
2
IL(MAX)
It is recommended that the peak repetitive reverse voltage
rating VRRM is higher than VOUT by a safety margin (a 10V
safety margin is usually sufficient).
The power dissipated by the diode is:
PD = IO(MAX) VD
and the diode junction temperature is:
TJ = TA + PD RθJA
The RθJA to be used in this equation normally includes the
RθJC for the device plus the thermal resistance from the
boardtotheambienttemperatureintheenclosure.TJmust
notexceedthediodemaximumjunctiontemperaturerating.
The choice of component(s) begins with the maximum
acceptable ripple voltage (expressed as a percentage of
the output voltage), and how this ripple should be divided
between the ESR step VESR and the charging/discharg-
ing VCOUT. For the purpose of simplicity, we will choose
2% for the maximum output ripple, to be divided equally
between VESR and VCOUT. This percentage ripple will
change, depending on the requirements of the applica-
tion, and the following equations can easily be modified.
For a 1% contribution to the total ripple voltage, the ESR
of the output capacitor can be determined using the fol-
lowing equation:
ESRCOUT
0.01 VOUT
ID(PEAK)
Boost Converter: Output Capacitor Selection
Contributions of ESR (equivalent series resistance), ESL
(equivalent series inductance) and the bulk capacitance
must be considered when choosing the correct output
capacitors for a given output ripple voltage. The effect of
thesethreeparameters(ESR,ESLandbulkC)ontheoutput
voltage ripple waveform for a typical boost converter is
illustrated in Figure 6.
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