• TI Thinks Resolved

# amc1301

hii alex

how are u doing

i want to use the amc1301 to sense a power ac line that has an amplitude ranges from 0 to 700 volts with frequency of 60 hz

as i see i need to use resistor divider  network at the input of the AMC1301 so when the ac line is 700v the max amplitude at VINP pin is 250mV .(i connect the VINN to ground )

but i have a problem with this design and my problem is when the power line amplitude reduces down to 100 volts or less i get very low input voltage at VINP about 5mV and its not very big swing at the input of the isolation amplifier .

do have any recommendation of how to sense high ac voltage like in my case

i can solve this issue by connecting a different resistor network  so when the amplitude voltage gets down to 100volts i start to use another resistor divider network that give me 250mV at the input of the amc1301

but i want to see if you have another approach  for sensing an voltage with an amplitude of 700 AC volts using the amc1301

• In reply to AIED BEBAR:

566volt main line sense1_AS.TSC

Hello Aied,

I believe the error is due to the AMC1301 bias current model. The AMC1301 has a typcal output bias current of 15uA on both VINP and VINN for a total of 30uA output bias current. I am unable to verify how much bias current the simulation model produces. If you look at the file I attached, the DC offset is mostly removed when I scale down the input resistance by a factor of 128. This is impractical for a real application due to thermal concerns of the resistors, but I thought it would help to at least simulate the OPA320 stage.

I also added an additional resistor to the VINN trace to help minimize the DC offset. This configuration can be seen in figure 52. of the datasheet. Look at equation 1 in section 10.2.2.1 Design Requirements to see the gain error equation. Since the input impedance of the AMC1301 is low, when a comparably sized resistor is used for the shunt then it creates an additional resistor divider. Try to get the shunt resistance as low as possible if you are going to use the AMC1301 for voltage sensing. Considering an isolated amplifier for voltage sensing (AMC1311, ISO224) is another route to go as well if you are unable to perform system calibrations.

I made a few changes to the OPA320 stage. I added VCM of 1.5V connected to the positive input terminal of the OPA320 which sets the common mode to 1.5V (halfway between 0 and 3V ADC input range) and changed the values of the feedback resistors to fit the fullscale range.  There seems to be some clipping on the negative side of the output swing (85.74mV) that is most likely due to the model. The OPA320 datasheet specifies less than 50mV for all cases of "Voltage output swing from both rails", so I am not sure why I am seeing 86mV. I do not support the OPA320, so I cannot speak to how accurate it's model is. Perhaps you can post to the amplifier forum and they will have an answer.

Best regards,

Alex Smith
Applications Engineer | Precision Delta-Sigma Converters

TI Precision Data Converters | TI Precision Labs - ADCs | Analog Engineer's Calculator Data Converters Learning Center | Selection Guide

• In reply to Alexander Smith:

i saw your modification on the circuit

it looks like the answer to my voltage sensing is using the AMC1311 that you suggested to me :)

i will try it , and if i will have questions i will get back to you , again thanks for your help.

• In reply to AIED BEBAR:

Happy to help Aied!

Have a good rest of your day.

Best regards,

Alex Smith
Applications Engineer | Precision Delta-Sigma Converters

TI Precision Data Converters | TI Precision Labs - ADCs | Analog Engineer's Calculator Data Converters Learning Center | Selection Guide

• In reply to Alexander Smith:

hii alex , hope you are doing will

alex i have a question

in the  AMC1311EVM board guide  there is a segment talking about isolation between the two VDD rails of the AMC1311 using push-pull driver witha center taped transformer

in my design i need about 5 components of AMC1311 for voltage measuring , and i don't think that for every AMC1311 amplifier i need to build supply isolation circuit that is on figure 3 of

http://www.ti.com/lit/ug/slau745/slau745.pdf

and my question is how many amc1311 isolation amplifiers i can connect to supply circuit that is Shown in figure 3?

• In reply to AIED BEBAR:

Hello Aied,

Thanks! I hope you are well too!

This depends on a few things, including what voltage you will be supplying. Looking at the SN6501 datasheet - it can supply up to 350mA on a 5V supply or 150mA on a 3.3V supply. The TLV704 LDO can handle up to 150mA on the  high side output. Then looking at the AMC1311 datasheet, the maximum current that will be drawn on VDD1 is 9.7mA.

This means that you could have up to 15 devices (150mA/9.7mA) using the recommended circuit. However this is for a perfect system and does not take losses and inefficiencies into account. I think 5 AMC1311 devices should be fine.

The attached app note may be helpful as well:SN6501_HV.pdf

Best regards,

Alex Smith
Applications Engineer | Precision Delta-Sigma Converters

TI Precision Data Converters | TI Precision Labs - ADCs | Analog Engineer's Calculator Data Converters Learning Center | Selection Guide

• In reply to Alexander Smith:

hii alex

i get you , i will proceed in my design with 5 amc components

if i will have more questions i will get back to you

• In reply to AIED BEBAR:

hii alex

i guess there is no ending to my questions :)

as i told you i am using the AMC 1311 to measure voltage of an ac industrial phase as you know there are three phases R S T and the return N and the actual ground.

lets say i want to measure the voltage deference between R and N , i am confused where to connect the GND1 of the VDD1 rail of the AMC1311
do i connect it to N line?

and lets say i want to measure also the deference between the N and the G in a another AMC1311 do i in this case connect the GND1 to GROUND of the power line ?
• In reply to AIED BEBAR:

Hi Aied,

I made a mistake in my previous post, I was not considering that you would be measuring different phases - I was only thinking in terms of current consumption. Since you are measuring different phases the measurement potential will be greatly different between the devices and therefor you will not be able to use the same power supply for your 5 AMC devices. The transformer on the EVM is single phase, which means you would need 1 per phase, a minimum of 3. If you use a 3phase transformer, then you would be able to use one tap per phase.

Take a look at this TIDesign, I think it will help illustrate my point: www.ti.com/.../tidu755.pdf

Best regards,

Alex Smith
Applications Engineer | Precision Delta-Sigma Converters

TI Precision Data Converters | TI Precision Labs - ADCs | Analog Engineer's Calculator Data Converters Learning Center | Selection Guide

• In reply to Alexander Smith:

hii alex

yes i can see in figure 6 of tidu755.pdf that each phase has a different  power supplies for the amc1311.

but i want to ask about the ground in each side of the AMC1311 isolation amplifier

in figure 6 of f tidu755.pdf  there is a voltage divider in the bottom of the design for measuring voltage

and i have two questions:

1- the ground of the VDD1 power supply on the left of the AMC beside the motor (ground of  the TPS7A3001 side ), is it connected to the neutral phase pf the motors ?

2- the ground on VDD2 on the right of the AMC (ground of  the SN6501DBV) , is it connected to the ground of the SitaraTM AM437x IDK ?? cause the output of the AMC goes to an ADC so that means that the ground of the ADC on SitaraTM AM437x IDK is connected to the ground of the SN6501DBV , am i right?

i am asking cause i am confused about the ground layers of each side of the AMC and my design is similar to the design presented in the   tidu755.pdf

• In reply to AIED BEBAR:

Hi Aied,

It should not be connected to the neutral, as it's voltage can change based upon phase loading. This could cause the circuit to violate the power supply limitations of the device based on the characteristics table. For additional examples of how to connect the circuit, take a look at figure 49. and 52. in the datasheet and make sure that the power supply limitations will not be violated.

The low side GND can be connected to the Sitara GND, but it really depends on your design and if you have one or two GNDs. For the two GND system an analog and digital gnd is used, then the two GNDs can be connected using a zero ohm resistor.

Best regards,

Alex Smith
Applications Engineer | Precision Delta-Sigma Converters