Hi all,

I am looking at the attached schematic for with the LT1461 Voltage Reference with a Shunt Current @100mA. In plain English, what is the U39 is used for? Does the device has a shutdown feature that can be used to switch full load currents or for system power down.

Thank you,
J

 

In plain English: "The purpose of U39 is to provide a stable reference voltage for the A/D converter U40. I'm guessing the stable output voltage of U39 is less than the +12V input voltage to U39. Do you have a copy of, and have you read the datasheet for the LT1461? If the answer is no, then here is a link:

https://www.analog.com/media/en/technical-documentation/data-sheets/LT1461.pdf

As you can tell the output voltage is a suffix to the part number which you have not provided. You may be unaware of the difference between a voltage reference, which may or may not supply the required current for the A/D converter to operate, and a voltage regulator which is designed to supply the required current but may not be as precise a reference as you might like. From page 1 of the datasheet the available output voltages are : "Voltage Options: 2.5V, 3V, 3.3V, 4.096V and 5V "

Notice the schematic on p. 18 of the datasheet which shows the use of the LT1461 as a reference in conjunction with a separate power connection to the LTC2400 16-bit A/D converter. I think powering a device from a reference is REALLY REALLY bad idea, if that is what is happening.

EDIT: Here is a link to the A/D converter datasheet from TI

https://www.ti.com/lit/ds/symlink/adc124s021.pdf?ts=1661536947979&ref_url=https%3A%2F%2Fwww.ti.com%2Fproduct%2FADC124S021

Please refer to Figure 49, on p.18 and notice that an LP2590 is a VOLTAGE REGULATOR, and NOT a voltage reference. Stop what you are currently doing and fix this before it is too late.

The following text from the datasheet should be noted:

A typical application of the ADC124S021 is shown in Figure 49. Power is provided in this example by the Texas Instruments LP2950 low-dropout voltage regulator, available in a variety of fixed and adjustable output voltages. The power supply pin is bypassed with a capacitor network located close to the ADC124S021. Because the reference for the ADC124S021 is the supply voltage, any noise on the supply will degrade device noise performance. To keep noise off the supply, use a dedicated linear regulator for this device, or provide sufficient decoupling from other circuitry to keep noise off the ADC124S021 supply pin. Because of the ADC124S021's low power requirements, it is also possible to use a precision reference as a power supply to maximize performance. The four-wire interface is also shown connected to a microprocessor or DSP.​

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This says that because of the low power requirements of the device, you can use a precision reference as the power supply. I think you may be OK. It took me a while to find it but at least you have an answer.

 

@Papabravo Thank you so much for the info in Plain English

 

@Papabravo Thank you so much for the info in Plain English

Sorry I couldn't get the whole post at one shot but had to engage in the process of stepwise refinement.