SN74HC595: EFT burst test problem

Swaminath Katte62

Part Number: SN74HC595
Other Parts Discussed in Thread: TPD4E05U06

Hi,

I am using SN74HC595 shift register for LED indications. Microcontroller sends serial 8 bit data to 74hc595 using SPI bus.

Problem- LED starts blinking when I apply EFT burst (500V 5KHz and 1KV 5KHz) to auxiliary port of device.

Observations- When I add 10pF capacitor close to RCLK pin of 74HC595 it works properly for 500V 5KHz burst but still getting problem for 1KV burst.

Kindly suggest any other method of filtering of EFT burst using ferrite bead and capacitor. Which type of ferrite bead I have to use for the same.

Thanks,

Swaminath

over 8 years ago

0 Michael J Schultis over 8 years ago

TI__Mastermind 24975 points

Hello Swaminath,

I am not an expert on EFT testing, but from what I have seen, it seems that this can be common with edge-rate controlled type devices.
Is the SN74HC595 device getting permanently damaged or is it just clocking when these pulses happen?

If the device is just clocking because of the pulses, I am not sure that the device is malfunctioning necessarily, so as you mentioned the EFT would just need to be filtered into the inputs of this device. Additionally, the ferrite bead is probably a good plan. There are surface mount ferrite beads available that you could put in front of edge triggered inputs (RCLK, SRCLK) and that should prevent the device from clocking in theory. I would just look on digikey or mouser for a ferrite bead that fits the profile.

Best,
Michael

0 Michael J Schultis over 8 years ago in reply to Michael J Schultis

TI__Mastermind 24975 points

Hello,

An additional suggestions to help with protection.

The TPD4E05U06 would be one suggestion for EFT protection up to 4kV: http://www.ti.com/lit/ds/symlink/tpd4e05u06.pdf

Otherwise as mentioned previously, a ferrite bead should help to suppress the signal.

Best,
Michael

0 Swaminath Katte62 over 8 years ago

Prodigy 120 points

Hello,

I have added ferrite beads in series with clock signal. Now it is ok for +/- 2KV burst . but not more than that. I need to test for +/-4KV.

0 Michael J Schultis over 8 years ago in reply to Swaminath Katte62

TI__Mastermind 24975 points

Swaminath,

To get this level of protection, you should use an external protection device.
I would suggest the following:
The TPD4E05U06 is tested for EFT protection up to 4kV: www.ti.com/.../tpd4e05u06.pdf

Best,
Michael

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SN74HC595: EFT burst test problem