ICE5QSxG

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Minloud
Level 1
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First reply posted First question asked Welcome!

Hello!
I have several questions about ICE5QSxG product:
1) What the difference between ICE5QSAG and ICE5QSBG revisions?
2) What method is used to calculate the turn on resistor in a MOSFET gate?
3) Regarding the question №2, what the gate driver current sink/source capability?
4) Did DEMO_5QSBG_60W1 pass radiated emissions for class B in the 30-1000 MHz band?

I use ICE5QSAG and IPP80R750P7 for flyback psu.
According to the ICE5QSAG feature, gate driver uses modulated, low current gate drive method that should prevent any turn on oscillations when passing trough the miller region. For my design I found, that mosfet series gate resistor with value higher than 2 Ohm causes 120-130MHz ringing in Miller region on turn-on and generates corresponding current oscillations. The lowest EMI level is ahieved when gate resistor replaced with short circuit. In attach you can find the mosfet drive layout. All connections are filled with polygons on both the top and bottom layers simultaneously. 

I would be grateful for design hints and answers.

Regards,
Artem

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Guruprasad_A
Moderator
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25 likes received 250 sign-ins 50 solutions authored

Hi @Minloud ,

Thank you for posting in the Infineon community.

No physical change on IC ICE5QSAG and ICE5QSBG. Upgrading revision for A to B is for firmware change.

QR_A is designed to switch ON primary MOSFET immediately once FB pin voltage exceeds VFB_LB=2.75V when the device is leaving ABM. In some cases, if the transformer is not fully demagnetized, then it may result in CCM operation. This impact is limited on the first switching ON event leaving ABM. This is solved in Revision B by detecting the valley before Switching ON MOSFET.

DEMO_5QSBG_60W1 is not tested for RE.

Regards,

Guruprasad A

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Guruprasad_A
Moderator
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25 likes received 250 sign-ins 50 solutions authored

Hi @Minloud ,

Thank you for posting in the Infineon community.

No physical change on IC ICE5QSAG and ICE5QSBG. Upgrading revision for A to B is for firmware change.

QR_A is designed to switch ON primary MOSFET immediately once FB pin voltage exceeds VFB_LB=2.75V when the device is leaving ABM. In some cases, if the transformer is not fully demagnetized, then it may result in CCM operation. This impact is limited on the first switching ON event leaving ABM. This is solved in Revision B by detecting the valley before Switching ON MOSFET.

DEMO_5QSBG_60W1 is not tested for RE.

Regards,

Guruprasad A

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Minloud
Level 1
Level 1
First reply posted First question asked Welcome!

Thank you for the reply. 

Can you also give me some guidelines about external gate resistor calculation?

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Guruprasad_A
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25 likes received 250 sign-ins 50 solutions authored

Hi @Minloud ,

Sorry for the late response.

The datasheet does not provide the peak current rating for the internal gate driver . We include the rise time and fall time with 1nF capacitor loading in the driver specification to assess the gate capability.

Recommended value for gate resistor is 11 ohms. In practice gate resistance can be varied to adjust the turn on speed of the MOSFET. (refer section 4.8 in Design guide more info )

Regards,

Guruprasad 

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Hi Guruprasad,
As I mentioned earlier, the most acceptable EMI level acheived with 0 ohm gate resistor.
In attach to this reply you can find gate diagrams with different Rg values:
From top to bottom: 0 ohm - 11 ohm - 22 ohm - 44 ohm.
Is that related to mosfet IPP80R750P7 or might it be a damaged IC? 

UPD:
I replaced the IC and MOSFET with STP12NK80Z at the same time and found no gate ringing with Rg = 11.
So is that the CoolMOS has higher EMI over SuperMESH, or my previous IC was damaged somehow?

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Guruprasad_A
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25 likes received 250 sign-ins 50 solutions authored

Hi @Minloud ,

The IC could be partially damaged.

Another explanation is that the noise in the gate is a result of the layout, parasitic parameters, and control loops. IPP80R750P7 MOSFET, might not be an optimal component.

Regards,

Guruprasad

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