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参数资料
| 型号： | LT3503EDCB#TRMPBF |
| 厂商： | Linear Technology |
| 文件页数： | 9/20页 |
| 文件大小： | 0K |
| 描述： | IC REG BUCK ADJ 1A 6DFN |
| 标准包装： | 1 |
| 类型： | 降压（降压） |
| 输出类型： | 可调式 |
| 输出数： | 1 |
| 输出电压： | 0.78 V ~ 16.2 V |
| 输入电压： | 3.6 V ~ 20 V |
| PWM 型： | 电流模式 |
| 频率 - 开关： | 2.2MHz |
| 电流 - 输出： | 1A |
| 同步整流器： | 无 |
| 工作温度： | -40°C ~ 85°C |
| 安装类型： | 表面贴装 |
| 封装/外壳： | 6-WFDFN 裸露焊盘 |
| 包装： | 标准包装 |
| 供应商设备封装： | 6-DFN-EP（2x3） |
| 产品目录页面： | 1331 (CN2011-ZH PDF) |
| 其它名称： | LT3503EDCB#TRMPBFDKR |
LT3503
APPLICATIO S I FOR ATIO
Now the required on time has decreased below the mini-
mum on time of 130ns. Instead of the switch pulse width
becoming narrower to accommodate the lower duty cycle
requirement, the switch pulse width remains fixed at
V SW
10V/DIV
I L
1A/DIV
130ns. In Figure 2 the inductor current ramps up to a value
exceeding the load current and the output ripple increases
to ~40mV. The part then remains off until the output
voltage dips below 100% of the programmed value before
it begins switching again.
V OUT
20mV/DIV
C OUT = 47 μ F
V OUT = 0.78V
V IN = 20V
I LOAD = 1.1A
L = 1.1 μ H
1 μ s/DIV
3503 F03
Provided that the output remains in regulation and that the
inductor does not saturate, operation above V IN(PS) is safe
and will not damage the part. Figure 3 illustrates the
switching waveforms when the input voltage is increased
to its absolute maximum rating of 20V.
V SW
10V/DIV
I L
1A/DIV
Figure 3
The part is robust enough to survive prolonged operation
under these conditions as long as the peak inductor
current does not exceed 2.2A. In Figure 3 the peak inductor
current of 2A suggests that the saturation current rating of
the inductor should be ~2.6A, which may require an
inductor of large physical size. The peak inductor current
V OUT
20mV/DIV
C OUT = 2 × 47 μ F
V OUT = 0.78V
V IN = 20V
I LOAD = 1.1A
L = 2.7 μ H
1 μ s/DIV
Figure 4
3503 F04
value can be reduced by simultaneously increasing the
inductance and output capacitance. In Figure 4 the peak
inductor current is reduced to 1.3A by doubling the output
capacitor and inductor values. Now the required inductor
current saturation rating is ~1.7A, so that even though the
inductance value has increased, it may be possible to
achieve a physically smaller inductor size.
Note that inductor current saturation ratings often de-
crease with temperature and that inductor current satura-
tion may further limit performance in this operating regime.
Inductor Selection and Maximum Output Current
A good first choice for the inductor value is:
L = 0.6 (V OUT + V D )
where V D is the voltage drop of the catch diode (~0.4V) and
L is in μ H. With this value there will be no subharmonic
oscillation for applications with 50% or greater duty cycle.
The inductor’s RMS current rating must be greater than
your maximum load current and its saturation current
should be about 30% higher. For robust operation in fault
conditions, the saturation current should be above 2.2A.
To keep efficiency high, the series resistance (DCR) should
be less than 0.1 ? . Table 1 lists several vendors and types
that are suitable.
Of course, such a simple design guide will not always
result in the optimum inductor for your application. A
larger value provides a higher maximum load current and
reduces output voltage ripple at the expense of slower
3503f
9
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