TPS2662: Power management forum

Mustafa Karahisar

Part Number: TPS2662

Hi TI forum,

I need to design an EFT filtering circuitry in front of the DC-DC power line to suppress industrial transients, according to standart IEC 61000-4-4.

I need performance criteria A (device is not affected any of the transients) suppression for at least level 3 (2 kV @ 5 kHz) eft bursts in my design.

So far with the help of the basic elements I can suppress level 1 transient waves (0.5 kV @ 5 kHz). In the design I use two ferrite beads one in the voltage side and one in the ground. Then I added varistor, tvs and common mode choke in parallel and series inductors again one in voltage side and one in the ground. Lastly I added capacitor block consists of 7 caps in parallel decreasing of factor 10, from 1000 uf to 1nf.

What improvements should I do to suppress these level 2 transients with criteria A performance?

We asked this question before and one of TI's workers recommended eFuses. After that I tried using efuse with tvs but I can't filter any transient waves with this. I used TPS26624 - EVM design. Increasing input capacitance(1uF to 10uF) helped a little bit but not much.

I'm using 24VDC input, 30V bipolar tvs diode(SMAJ30CA, in and out side), 10uF input side capacitor and 2.2uF output side capacitor(both electrolytic maybe this can be a problem), 4k7 ohm current limiting resistor, 4.7uF ceramic dVdT cap.

Question is "what am i doing wrong?"

over 5 years ago

0 Lokesh Ghulyani over 5 years ago

TI__Expert 8630 points

Hello Mustafa,

You can refer to schematic in Figure 10 on Page 6 of Simplifying EFT, Surge and Power-Fail Protection Circuits in PLC Systems (Rev. C). This schematic can be tested using TPS26624-25EVM or TPS26620-23EVM.

Let us know if you still face issues in achieving Criteria A performance.

0 Mustafa Karahisar over 5 years ago in reply to Lokesh Ghulyani

Prodigy 60 points

Thanks for reply Lokesh,

I tried this already. Only difference in my circuit, R5 connected between FLT and IN pin.

Best Regards.

0 Lokesh Ghulyani over 5 years ago in reply to Mustafa Karahisar

TI__Expert 8630 points

Hello Mustafa,

Can you please share the schematic and waveforms of VIN,VOUT, FLTb and input current during the EFT pulses?

4k7 resistor is not recommended on ILIM pin. Resistor on ILIM needs to greater than 7.5k Ohms. Please see Table 7.3 on page 5 of the datasheet of TPS2662.

0 Mustafa Karahisar over 5 years ago in reply to Lokesh Ghulyani

Prodigy 60 points

Hi Lokesh,

Input current is 0.2A,

VIN is yellow channel and VOUT is red channel. Coupling = AC. Resistor on ILIM pin is 20k. V/div = 1V

TX_led blinking when EFT pulses come. Device thinks data coming, this problem frequently encountered also with other devices.

Test IEC61000-4-4 level 2 (1kV @ 5kHz)

DC Coupling, V/Div = 10, RILIM = 20K

Schematic:

0 Lokesh Ghulyani over 5 years ago in reply to Mustafa Karahisar

TI__Expert 8630 points

Hello Mustafa,

Do you want prevent EFT pulses from coming on OUT of TPS2662?

The circuit described in App note: Simplifying EFT, Surge and Power-Fail Protection Circuits in PLC Systems (Rev. C). allows the EFT pulses to pass through TPS2662.

0 Mustafa Karahisar over 5 years ago in reply to Lokesh Ghulyani

Prodigy 60 points

Hello Lokesh Thanks,

Yes, I want to prevent EFT pulses from coming on OUT.

So all of this conversation was misunderstanding, TPS2662 can't block or supress EFT pulses, is it correct?

Best Regards.

0 Lokesh Ghulyani over 5 years ago in reply to Mustafa Karahisar

TI__Expert 8630 points

Hello Mustafa,

Is there any load connected on output of TPS2662 which needs to be powered during EFT pulses?

In typical applications, a load is connected on output of TPS2662 which needs to be powered during EFT pulses and therefore TPS2662 circuit was designed to pass the EFT pulses and provide power to the load.

If there is no load connected on Output of TPS2662 and if it is required to turn off the output during EFT pulses, we can suggest some changes in the circuit for this.

0 Mustafa Karahisar over 5 years ago in reply to Lokesh Ghulyani

Prodigy 60 points

Hello Lokesh,

No, load's need to be powered during EFT pulses. TPS2662 is useless for us now.

Can you advice any other product or circuit or filter about this? We already tried some filters, but we managed supress just level 2 waves. We need to supress at least level 3 waves.

0 Lokesh Ghulyani over 5 years ago in reply to Mustafa Karahisar

TI__Expert 8630 points

Hello Mustafa,

Below are few suggestions for TPS2662 for suppressing EFT pulses:

Add a small cap (10-22pF) between IN and ULVO pins (parallel to R2).
Set UVLO and OVP trip levels by R2/R3/R4 within ±1V of input voltage.
Reduce C1, C3 to 0.1uF

0 Mustafa Karahisar over 5 years ago in reply to Lokesh Ghulyani

Prodigy 60 points

Hello Lokesh,

I tried your suggestions but even worse now. I can clearly see spikes now.

0 Lokesh Ghulyani over 5 years ago in reply to Mustafa Karahisar

TI__Expert 8630 points

Hello Mustafa,

Just to confirm, the YELLOW trace is for output voltage.

In place of TPS2662, you would probably need a fast comparator, a fast gate drive and a MOSFET to prevent EFT pulses. The compactor and gate drive should be fast enough to turn-off the MOSFET with in 100ns.