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# TIDA-00555: Reg AC voltage sensing in TIDA-00555,TI has used 1.66Mohm(5 number of 332K in series) and current is low around 230uA.

Part Number: TIDA-00555
Other Parts Discussed in Thread: TIDA-00366, AMC1100

Dear TI team,

Good evening.

In Tida-00555,in voltage sensing you have used 332K five number in series to reduce AC voltage and connected 1K across to get around 230mV for maximum 270V AC RMS.

While we do kirchoff voltage law(KVL),we can find out that current is around 230uA(270V AC RMS).

So you have used 332k,1206 package,1% tolerance thick film resistor 5 number in series which is 1.66Mohm.can we use 1Mohm(thin film) and two 332K(thin film) in series or only one 1.66Mohm thin film  resistor with 1k  voltage divider?

Can we use lesser value like 100k(5 number) in series to get 500K and 280 ohm across to get 210mV approximately?

I'm getting noisy waveform after 1.66Mohm and 1k ohm voltage divider,may I use above 100k(5 number)and 280 ohm voltage divider combination?

is Tida-00555  and Tida-00366 fully tested? can you share output wave forms and more details of Tida-00555?

Thank you,

Girish K

caliber

• Girish,

1) can we use 1Mohm(thin film) and two 332K(thin film) in series or only one 1.66Mohm thin film  resistor with 1k  voltage divider?

Potentially, but there are a couple things to be aware of. We chose Panasonic ERJ-8ENF3323V as our series resistors. If you look at the datasheet for that family of resistors, you can see that Panasonic specifies the "Limiting Element Voltage" at 200V. You wouldn't be able to use that family of resistors with value 1.66 Mohm since you would be dropping more than 200V across the resistor. If you can find resistors with a high enough rated nominal voltage, high enough rated power dissipation, and ensure the resistor isn't operating above specified maximum temperature, you can try to reduce the number of resistors. You should also be careful since dropping higher voltages across a single resistor means higher voltage potentials will be closer together on your PCB, raising the chances for arcing, breakdown, and accidental probe discharge of unsafe voltages.

2) Can we use lesser value like 100k(5 number) in series to get 500K and 280 ohm across to get 210mV approximately?

As long as you choose resistors that are capable to handle the higher dissipated power, the design will work with lower resistance values like the ones you mention. TI chose 1.66 Mohm to reduce loading on the AC source.

3) I'm getting noisy waveform after 1.66Mohm and 1k ohm voltage divider,may I use above 100k(5 number)and 280 ohm voltage divider combination?

Have you tried replacing FB9 with a ferrite bead like on page 16 of TIDA-00555? You will need to change R60 to keep the output voltage within +/- 250 mV for the AM1100. TIDA-00555 calls out the TDK MMZ1608B102C in the BOM, although you may need a different ferrite depending on the frequency of the noise you are seeing.

4) Is Tida-00555  and Tida-00366 fully tested? can you share output wave forms and more details of Tida-00555?

The test setup and results are specified in TIDA-00555 sections 6 and 7. Which tests and waveforms are you looking for specifically?

• Hi Benjamin Uhing,

Good morning.

Kindly accept my friend request and will send you schematics to check.

We have used AMC1100 of TIDA-00555 and differential amplifier section with low pass filter of TIDA-00366 voltage sensing section.

So i would like to send you our design,waveform and results to cross verify to find any possible solution to solve problem.

Thank you very much.

Girish K

Caliber