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参数资料
| 型号： | LT3804EFE#TRPBF |
| 厂商： | Linear Technology |
| 文件页数： | 10/16页 |
| 文件大小： | 0K |
| 描述： | IC REG CTRLR ISO PWM 28-TSSOP |
| 标准包装： | 2,000 |
| PWM 型： | 电流/电压模式 |
| 输出数： | 2 |
| 频率 - 最大： | 570kHz |
| 占空比： | 80% |
| 电源电压： | 8 V ~ 25 V |
| 降压： | 是 |
| 升压： | 无 |
| 回扫： | 无 |
| 反相： | 无 |
| 倍增器： | 无 |
| 除法器： | 无 |
| Cuk： | 无 |
| 隔离： | 是 |
| 工作温度： | -40°C ~ 125°C |
| 封装/外壳： | 28-SOIC（0.173"，4.40mm 宽）裸露焊盘 |
| 包装： | 带卷 (TR) |
LT3804
APPLICATIO S I FOR ATIO
? I L =
? I LMAX
I RMS ≥ I O +
I SAT O +
? I LMAX
Output Inductor Selection
The key parameters for choosing the inductor include
inductance, RMS and saturation current ratings, and DCR.
The inductance must be selected to achieve a reasonable
value of ripple current, which is determined by:
V OUT ? (1 – D )
f ? L
Where V OUT is the output voltage, D is the duty cycle, f is
switching frequency and L is the inductance. Typically, the
inductor ripple current is designed to be 20% to 40% of the
maximum output current.
The RMS current rating must be high enough to deliver the
maximum output current. A sufficient saturation current
rating should prevent the inductor core from saturating.
These two current ratings can be determined by:
2
2
12
≥ I
2
where I O is the maximum DC output current and ? I LMAX is
the maximum peak-to-peak inductor ripple current. To
optimize the efficiency, we usually choose the inductor
with the minimum DCR if the inductance and current
ratings are the same.
Output N-Channel MOSFET Drivers
The LT3804 employs high speed N-channel MOSFET
synchronous drivers to achieve high system efficiency.
GBIAS is the 8V regulator output to bias and supply the
capacitor to the ground plane. A Schottky catch diode is
required on the switch node.
Power MOSFET Selection
The LT3804 drives two external N-channel MOSFETs to
deliver high currents at high efficiency. The gate drive
voltage is typically 6.5V. The key parameters for choosing
MOSFETs include drain to source voltage rating V DSS and
R DS(ON) at 6.5V gate drive. Note that the transformer
secondary voltage waveform will overshoot at its rising
edge due to the ringing between transformer leakage
inductance and parasitic capacitance. The V DSS of both
top and bottom MOSFETs must be sufficiently higher than
the maximum overshoot. It is recommended that an RC
snubber or voltage clamping circuitry be placed across the
transformer secondary winding to limit the V S overshoot.
The R DS(ON) of the MOSFETs should be selected to deliver
the required current at the desired efficiency as well as to
meet the thermal requirement of the MOSFET package.
The conduction power losses of the MOSFETs are:
P M1 ? I O2 ? R DS(ON)M1 ? D
P M2 ? I O2 ? R DS(ON)M2 ? (1 – D)
where I O is the maximum output current of LT3804 circuit,
and R DS(ON)M1 and R DS(ON)M2 are the on-resistance for
the top and bottom MOSFETs, respectively. The R DS(ON)
must be determined with 6.5V gate drive at the expected
operating temperature. Numerous high performance power
MOSFETs are available from Siliconix, International Rec-
tifier and Fairchild. If the V DSS and R DS(ON) ratings are the
same, the MOSFETs with the lowest gate charge Q G should
be chosen to minimize the power loss associated with the
MOSFET gate drives, the switching transitions, and the
controller bias supply.
drivers and should be properly bypassed with a low ESR
3804i
10
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| LT381 | 制造商:SEOUL 制造商全称:Seoul Semiconductor 功能描述:RED OVAL LAMP LED |
| LT382 | 制造商:Mode Electronics 功能描述:MODE LONER TIP .02 CONICAL 制造商:EDSYN 功能描述:SOLDERING TIP, Series:Loner, Tip / Nozzle Length:0.62" |
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