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The information presented in this cross reference is based on TOSHIBA's selection criteria and should be treated as a suggestion only. Please carefully review the latest versions of all relevant information on the TOSHIBA products, including without limitation data sheets and validate all operating parameters of the TOSHIBA products to ensure that the suggested TOSHIBA products are truly compatible with your design and application.Please note that this cross reference is based on TOSHIBA's estimate of compatibility with other manufacturers' products, based on other manufacturers' published data, at the time the data was collected.TOSHIBA is not responsible for any incorrect or incomplete information. Information is subject to change at any time without notice.
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What is PSRR of an LDO?
PSRR of an LDO
PSRR (Power Supply Rejection Ratio) is a measure of an LDO regulator’s ability to suppress ripple noise from the input voltage at its output.
A higher PSRR indicates better noise suppression capability.
In our datasheets, this characteristic is expressed as Ripple Rejection Ratio (R.R.), which has the same meaning as PSRR.
如果发生过流，折返功能（foldback）会保护我们的LDO稳压器。
“折返”一词源自保护操作期间折返的输出电流（IOUT）与输出电压（VOUT）曲线形状，如图1所示。
在短路负载条件下，折返会随着VOUT降低的而减小IOUT。当VOUT降至零时，折返会将输出电流保持在一个有限的恒定水平。
当过流状态消失后，VOUT会自动恢复至正常电平。
如果输出引脚上连接了输出电容器或电容性负载，则VOUT会升高，而折返功能会限制IOUT。
Definition of PSRR
PSRR is defined by the following equation.
For example, if the input ripple voltage is 200 mV and the output ripple voltage is 0.2 mV, the PSRR would be 60 dB.
Frequency Characteristics of PSRR
PSRR has frequency characteristics, meaning the suppression level varies depending on the frequency of the ripple noise.
Even when using the same LDO, differences in the switching frequency of the power supply (e.g., switching regulator) can result in different ripple frequencies, which in turn affect the attenuation performance.
It is important to keep in mind the frequency characteristics of PSRR when selecting and using an LDO.
Introduction of High-PSRR LDOs
We have released several high PSRR LDO regulators such as TCR3RM series, TCR5RG series, and TCR5FM series. The main characteristics are as follows.
| Series | TCR3RM series | TCR5RG series | TCR5FM series | ||
|---|---|---|---|---|---|
| Package | Name | DFN4C, DFN4F | WCSP4F | DFN4D | |
| Size typ. (mm) | 1.0×1.0×0.38 | 0.645×0.645×0.33 | 1.0×1.0×0.37 | ||
| Operating ranges | Input voltage VIN (V) | 1.8～5.5 | 1.8～5.5 | 1.55～5.5 | |
| Output current IOUT (mA) | 300 | 500 | 500 | ||
| Operation temperature Topr (°C) | -40～85 | -40～85 | -40～125 | ||
| Electrical characteristics （Unless otherwise specified, Tj=25°C、VIN= 3.3V、VOUT=2.8V） |
Output voltage VOUT (V) | 0.9～4.5 | 0.9～5.0 | 0.9～5.0 | |
| Output voltage accuracy VOUT (%) |
IOUT=1～500mA Tj=-40～125°C |
±2 | ±1.5 | ±2.2 | |
| Quiescent current IB(ON) typ. (μA) |
IOUT=0mA | 7 | 7 | 10 | |
| Stand-by current IB(OFF) typ. (μA) |
VCT=0V | 0.1 | 0.08 | 0.1 | |
| Drop-out voltage VDO typ. (mV) |
IOUT=300mA or 500mA | 130 | 150 | 220 | |
| Ripple rejection ratio R.R. typ. (dB) |
IOUT=10mA, VRipple=200mVp-p, f=1kHz | 100 | 100 | 91 | |
| IOUT=10mA, VRipple=200 mVp-p, f=10kHz | 93 | 93 | 89 | ||
| IOUT=10mA, VRipple=200 mVp-p, f=100kHz | 68 | 67 | 67 | ||
| IOUT=10mA, VRipple=200 mVp-p, f=1MHz | 68 | 59 | 59 | ||
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