Author Topic: 14.4V ground reference for ADC (Read 12462 times)

Simon · « **Reply #125 on:** May 31, 2019, 06:59:23 am »

Quote from: Arjunan M R on May 31, 2019, 02:11:44 am

Quote from: Simon on May 30, 2019, 04:59:45 pm
Quote from: Arjunan M R on May 30, 2019, 04:50:35 pm
I am using a 100nF ceramic and 10uF tantalum for bypassing ADC , DAC and VRef.
Is that enough?

Do you mean you have one 100nF ceramic and one 10uF tantalum for all 3 or that they have a pair each?
A pair of 100n and 10uF for 3 of those.

No, you want at least one 100nF per chip as close to the pins as possible, if the chips are all close you may get away with a single 10µF capacitor.

Arjunan M R · « **Reply #126 on:** May 31, 2019, 06:59:47 am »

Quote from: Simon on May 31, 2019, 06:57:56 am

Quote from: Arjunan M R on May 31, 2019, 06:55:37 am
Quote from: Simon on May 31, 2019, 06:54:31 am
Quote from: Arjunan M R on May 31, 2019, 06:44:26 am
Is adding a TVS diode to the input and output a good idea?

Input of what?
input of psu

If you are powering it off a mains transformer it should not be neccessary. No harm in using one if you want to. Be sure to understand all the specs of the TVS, they don't trigger on/off at a single threshold.

I am using a AC to DC adapter 19 V 2 A

Arjunan M R · « **Reply #127 on:** May 31, 2019, 07:03:28 am »

Quote from: Simon on May 31, 2019, 06:59:23 am

Quote from: Arjunan M R on May 31, 2019, 02:11:44 am
Quote from: Simon on May 30, 2019, 04:59:45 pm
Quote from: Arjunan M R on May 30, 2019, 04:50:35 pm
I am using a 100nF ceramic and 10uF tantalum for bypassing ADC , DAC and VRef.
Is that enough?

Do you mean you have one 100nF ceramic and one 10uF tantalum for all 3 or that they have a pair each?
A pair of 100n and 10uF for 3 of those.

No, you want at least one 100nF per chip as close to the pins as possible, if the chips are all close you may get away with a single 10µF capacitor.

Yes, I am using 100nF for every chips.

Arjunan M R · « **Reply #128 on:** May 31, 2019, 07:41:56 am »

Here is the TVS diode I am going to use. I have read the full datasheet.
It has a breakdown voltage of 22.2 to 24.5V. Max. reverse leakage current of 1µA. Max. clamping voltage of 32.4V. And maximum peak pulse surge current of 12.3A.
That will be good enough for my purpose.

Simon · « **Reply #129 on:** May 31, 2019, 12:41:53 pm »

Quote from: Arjunan M R on May 31, 2019, 07:41:56 am

Here is the TVS diode I am going to use. I have read the full datasheet.
It has a breakdown voltage of 22.2 to 24.5V. Max. reverse leakage current of 1µA. Max. clamping voltage of 32.4V. And maximum peak pulse surge current of 12.3A.
That will be good enough for my purpose.

No it won't, check the reverse standoff voltage. it will turn on at 22.2-24.5V but will not turn off again until 2-3 volts lower, if this is near the peak voltage of the supply you can get it triggered permanently.

Arjunan M R · « **Reply #130 on:** May 31, 2019, 12:48:34 pm »

Quote from: Simon on May 31, 2019, 12:41:53 pm

Quote from: Arjunan M R on May 31, 2019, 07:41:56 am
Here is the TVS diode I am going to use. I have read the full datasheet.
It has a breakdown voltage of 22.2 to 24.5V. Max. reverse leakage current of 1µA. Max. clamping voltage of 32.4V. And maximum peak pulse surge current of 12.3A.
That will be good enough for my purpose.

No it won't, check the reverse standoff voltage. it will turn on at 22.2-24.5V but will not turn off again until 2-3 volts lower, if this is near the peak voltage of the supply you can get it triggered permanently.

its 20V(standoff voltage)

Arjunan M R · « **Reply #131 on:** May 31, 2019, 12:58:22 pm »

there is no tvs diode with low standoff voltage with min breakdown voltage more than 20V in RS components. I might abandone the idea of tvs diode.

Simon · « **Reply #132 on:** May 31, 2019, 01:27:05 pm »

Really? usually the reverse standoff in a few volts less than the breakdown voltage.

Arjunan M R · « **Reply #133 on:** May 31, 2019, 01:33:33 pm »

Quote from: Simon on May 31, 2019, 01:27:05 pm

Really? usually the reverse standoff in a few volts less than the breakdown voltage.

I mean that the value in the datasheet says 20V.

Simon · « **Reply #134 on:** May 31, 2019, 01:35:54 pm »

where? remember hat one datasheet will over many parts

Simon · « **Reply #135 on:** May 31, 2019, 01:42:06 pm »

https://uk.rs-online.com/web/c/semiconductors/discrete-semiconductors/tvs-diodes/?redirect-relevancy-data=636F3D3126696E3D4931384E53656172636847656E65726963266C753D656E266D6D3D6D61746368616C6C7061727469616C26706D3D5E2E2A2426706F3D31333326736E3D592673723D52656469726563742673743D43415443485F414C4C5F44454641554C542673633D592677633D4E4F4E45267573743D7476732064696F6465267374613D7476732064696F646526&r=f&searchHistory=%257B%2522enabled%2522%253Atrue%257D&applied-dimensions=4294702910

Arjunan M R · « **Reply #136 on:** May 31, 2019, 01:43:17 pm »

wait i forgot the part number

Arjunan M R · « **Reply #137 on:** May 31, 2019, 01:44:44 pm »

Quote from: Simon on May 31, 2019, 01:42:06 pm

https://uk.rs-online.com/web/c/semiconductors/discrete-semiconductors/tvs-diodes/?redirect-relevancy-data=636F3D3126696E3D4931384E53656172636847656E65726963266C753D656E266D6D3D6D61746368616C6C7061727469616C26706D3D5E2E2A2426706F3D31333326736E3D592673723D52656469726563742673743D43415443485F414C4C5F44454641554C542673633D592677633D4E4F4E45267573743D7476732064696F6465267374613D7476732064696F646526&r=f&searchHistory=%257B%2522enabled%2522%253Atrue%257D&applied-dimensions=4294702910

https://in.rsdelivers.com/category/tvs-diodes/9849#PI-1|PS-20|viewtype-0

Arjunan M R · « **Reply #138 on:** May 31, 2019, 01:58:17 pm »

I think it will turn off at 20.5V
Is that ok?

Arjunan M R · « **Reply #139 on:** May 31, 2019, 02:01:57 pm »

I will choose one with higher standoff voltage.

Arjunan M R · « **Reply #140 on:** May 31, 2019, 02:04:22 pm »

Quote from: Simon on May 31, 2019, 01:27:05 pm

Really? usually the reverse standoff in a few volts less than the breakdown voltage.

I thought that the reverse standoff voltage is the difference between when the TVS turns on and turns of.

There is diodes with higher standoff in rs components

Quote from: Simon on May 31, 2019, 01:42:06 pm

https://uk.rs-online.com/web/c/semiconductors/discrete-semiconductors/tvs-diodes/?redirect-relevancy-data=636F3D3126696E3D4931384E53656172636847656E65726963266C753D656E266D6D3D6D61746368616C6C7061727469616C26706D3D5E2E2A2426706F3D31333326736E3D592673723D52656469726563742673743D43415443485F414C4C5F44454641554C542673633D592677633D4E4F4E45267573743D7476732064696F6465267374613D7476732064696F646526&r=f&searchHistory=%257B%2522enabled%2522%253Atrue%257D&applied-dimensions=4294702910

Arjunan M R · « **Reply #141 on:** May 31, 2019, 02:13:57 pm »

I chose this one.
It has a maximum reverse standoff voltage of 24V. Minimum breakdown voltage of 26.5V and maximum clamping voltage of 70V.
This will be okay.

Arjunan M R · « **Reply #142 on:** May 31, 2019, 02:24:04 pm »

Quote from: Arjunan M R on May 31, 2019, 02:13:57 pm

I chose this one.
It has a maximum reverse standoff voltage of 24V. Minimum breakdown voltage of 26.5V and maximum clamping voltage of 70V.
This will be okay.

Its differential resistance is too high

Arjunan M R · « **Reply #143 on:** May 31, 2019, 02:58:51 pm »

Ok, final decision.
I am going to use this TVS diode sm15t30ca
https://in.rsdelivers.com/product/stmicroelectronics/sm15t30ca/stmicroelectronics-sm15t30ca-bi-directional-tvs/4861253
Diode Configuration
Single
Maximum Operating Temperature
+150 °C
Number of Elements per Chip
1
Length
7.15mm
Maximum Clamping Voltage
53.5V
Minimum Breakdown Voltage
28.5V
Brand
STMicroelectronics
Maximum Peak Pulse Current
187A
Package Type
SMC
Mounting Type
Surface Mount
Minimum Operating Temperature
-55 °C
Width
6.25mm
Test Current
1mA
Maximum Reverse Stand-off Voltage
25.6V
Maximum Reverse Leakage Current
1µA
Height
2.45mm
Pin Count
2
Dimensions
7.15 x 6.25 x 2.45mm
Direction Type
Bi-Directional
Peak Pulse Power Dissipation
1500W

Arjunan M R · « **Reply #144 on:** May 31, 2019, 03:28:49 pm »

Here is the datasheet of sm15t30ca
https://documents.rs-online.com/techlib://itc_doclist_GB.htm?stockno=4861253

Arjunan M R · « **Reply #145 on:** June 01, 2019, 06:04:47 am »

Can I use 6.3V tantalum capacitor to bypass 5V supply?

Simon · « **Reply #146 on:** June 01, 2019, 08:03:20 am »

Just google tantalum capacitors, there will be lots of information. I don't know as i don't use them.

Arjunan M R · « **Reply #147 on:** June 01, 2019, 08:12:50 am »

This is what it says on "Voltage Derating Rules for Solid Tantalum and Niobium Capacitors" by AVX.

Simon · « **Reply #148 on:** June 01, 2019, 01:33:08 pm »

You can probably run closer to maximum with a stable voltage, if you are smoothing a fluctuating voltage you may want more headroom for surges/spikes.

Arjunan M R · « **Reply #149 on:** June 02, 2019, 05:10:29 am »

Hi, the LDO i am using (LT3080) needs a minimum output curent of 1mA.I was going to use lm334z as a constant current source.But it is only available in higher quantities.
Can i use a electronic potentiometer as a constant current source?
Or is there any simple circuits i can use as constant current source?


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Author Topic: 14.4V ground reference for ADC (Read 12462 times)

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