参数资料
型号: LT1175CT-5#PBF
厂商: Linear Technology
文件页数: 14/20页
文件大小: 0K
描述: IC REG LDO -5V .5A TO220
标准包装: 50
稳压器拓扑结构: 负,固定式
输出电压: -5V
输入电压: 可下调至 -20V
电压 - 压降(标准): 0.5V @ 500mA
稳压器数量: 1
电流 - 输出: 500mA
电流 - 限制(最小): 可调式
工作温度: 0°C ~ 70°C
安装类型: 通孔
封装/外壳: TO-220-5 成形引线
供应商设备封装: TO-220-5
包装: 管件
产品目录页面: 1326 (CN2011-ZH PDF)
LT1175
APPLICATIONS INFORMATION
To estimate regulator output ripple under different
conditions, the following general comments should be
helpful:
1. Output ripple at high frequency is only weakly affected
loads, larger resistors and smaller capacitors can be used
to save space. At heavier loads an inductor may have to
be used in place of the resistor. The value of the inductor
can be calculated from:
2 π ( ) ( 10 rr / 20
by load current or output capacitor size for medium
to heavy loads. At very light loads (<10mA), higher
frequency ripple may be reduced by using larger output
L FIL =
f
ESR
)
capacitors.
2. A feedforward capacitor across the resistor divider used
with the adjustable part is effective in reducing ripple
only for output voltages greater than 5V and only for
ESR = Effective series resistance of ?lter capacitor. This
assumes that the capacitive reactance is small com-
pared to ESR, a reasonable assumption for solid
tantalum capacitors above 2.2μF and 50kHz.
frequencies less than 100kHz.
3. Input-to-output voltage differential has little effect on
ripple rejection until the regulator actually enters a
f
rr
= Ripple frequency
= Ripple rejection ratio of ?lter in dB
dropout condition of 0.2V to 0.6V.
Example: ESR = 1.2Ω, f = 100kHz, rr = – 25dB.
6 . 3 ? ? 10 ? ? 10 ? 25 / 20 ??
Ifripplerejectionneedstobeimproved,aninput?ltercan
be added. This ?lter can be a simple RC ?lter using a 1Ω
to 10Ω resistor. A 3.3Ω resistor for instance, combined
L FIL =
1 . 2
5 ? ?
= 34 μ H
with a 0.3Ω ESR solid tantalum capacitor, will give an ad-
ditional 20dB ripple rejection. The size of the resistor will
be dictated by maximum load current. If the maximum
voltage drop allowable across the resistor is “V R ,” and
maximum load current is I LOAD , R = V R /I LOAD . At light
Solid tantalum capacitors are suggested for the ?lter to
keep ?lter Q fairly low. This prevents unwanted ringing at
the resonant frequency of the ?lter and oscillation problems
with the ?lter/regulator combination.
1175ff
14
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