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Low-noise positive/negative power supply circuits will be necessary for circuits such as micro sensors and CCD sensors used in noise-sensitive audio equipment, medical and precision equipment, etc. Have you ever had trouble designing a low-noise plus/minus output LDO in such a case?
Selection of ultra-high PSRR LDO
As one indicator for selecting a low-noise LDO, it is important to select a device with a large PSRR (Power Supply Ripple Rejection) value. PSRR is expressed as the following formula and represents the ratio of input noise to output noise. For example, if PSRR=100 (dB) and input ripple VIN=1 (V), the ripple appearing at the output will be VOUT=10μV.
Formula: PSRR calculation formula
Also, one point to be aware of regarding the PSRR characteristics is that the PSRR decreases as the load current increases. There are products in the world where the PSRR becomes zero when only about 10mA of load current is applied, so care must be taken when selecting. If such an LDO is used, the ripple of the input switching power supply will appear in the output as is, causing malfunction of sensors and other devices.
Figure 1 shows the PSRR characteristics of an LDO product. The PSRR characteristics of this product are also good, but when comparing the load current Iload of 0.1 (A) and 1.5 (A), there is a difference of 10 (dB) at the 1KHz point.
For applications requiring a low noise power supply, it is recommended to choose a high PSRR LDO.
In addition, there are many candidates for positive output LDOs, but there are few candidates for negative output LDOs, and it is difficult to select an LDO with a high PSRR value, so be careful.
Low Noise Plus/Minus LDO Solution
Analog Devices has LDO products with high PSRR values.
The product is called LT3045 for positive output and LT3094 for negative output. Both LDOs have low noise of 0.8μVRMS (10Hz to 100kHz) and achieve high PSRR.
This product is recommended as a positive/minus low noise power supply.
±12V Power Reference Board for Precision, Low Noise Circuits
This time, we have developed a reference board capable of ±12V output with LT3045 as positive output and LT3094 as negative output.
By connecting this board to an audio equipment, CCD, or minute signal sensor processing circuit and evaluating it, it is possible to check the low noise characteristics on the system.
At the end
In this article, we introduced a low-noise ±12V power supply reference board developed for audio equipment, medical equipment, and precision equipment. If you would like more information about the products we have introduced, please contact us here.
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