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Power Management ICs Forum Discussions

KUOWENYUNG
Level 3
Level 3
100 sign-ins 50 sign-ins 10 replies posted

Dear Sir,

Except the inductor current waveform none-linear rise up, Is there any other way to judgement inductor saturation?
can you share some case about inductor saturation relative voltage waveform? thanks!

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1 Solution
Nishanth
Moderator
Moderator
Moderator
50 replies posted 25 solutions authored 10 likes received

Hello,

Thank you for posting in Infineon community.

When an inductor reaches saturation, its inductance drops and ripple current rises. The inductor will begin to act more like a resistor. Due to a decline in energy storage capacity, efficiency will also decrease. High current peaks will develop on the switch node as the inductance is reduced.

The Over Current Protection (OCP) circuitry in the IR3889 detects inductor saturation by monitoring Rds(on) of the synchronous MOSFET, which is proportional to inductor current. If the current of the Synchronous MOSFET exceeds the chosen OCP limit, the IR3889 skips the PWM pulse and extends the Synchronous MOSFET's on time until the current falls below the OCP limit. The OCP operation is also shown in the figure below.

Nishanth_0-1650306643926.png

During normal operation, the PGood signal, which has an open drain is high. When an inductor is saturated, the output voltage Vo falls below the PGood turn-off threshold. This will cause PGood to go low. Furthermore, the output voltage will eventually fall below the Under-Voltage Protection (UVP) threshold, causing UVP to activate. The IR3889 then enters hiccup mode with a blanking time of 20ms. After 20ms of blanking it will try to turn on and will repeat the hiccup mode until core remains saturated.

I hope this explanation was useful. Please let me know if you have any further queries.

Regards,

Nishanth Kulkarni

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1 Reply
Nishanth
Moderator
Moderator
Moderator
50 replies posted 25 solutions authored 10 likes received

Hello,

Thank you for posting in Infineon community.

When an inductor reaches saturation, its inductance drops and ripple current rises. The inductor will begin to act more like a resistor. Due to a decline in energy storage capacity, efficiency will also decrease. High current peaks will develop on the switch node as the inductance is reduced.

The Over Current Protection (OCP) circuitry in the IR3889 detects inductor saturation by monitoring Rds(on) of the synchronous MOSFET, which is proportional to inductor current. If the current of the Synchronous MOSFET exceeds the chosen OCP limit, the IR3889 skips the PWM pulse and extends the Synchronous MOSFET's on time until the current falls below the OCP limit. The OCP operation is also shown in the figure below.

Nishanth_0-1650306643926.png

During normal operation, the PGood signal, which has an open drain is high. When an inductor is saturated, the output voltage Vo falls below the PGood turn-off threshold. This will cause PGood to go low. Furthermore, the output voltage will eventually fall below the Under-Voltage Protection (UVP) threshold, causing UVP to activate. The IR3889 then enters hiccup mode with a blanking time of 20ms. After 20ms of blanking it will try to turn on and will repeat the hiccup mode until core remains saturated.

I hope this explanation was useful. Please let me know if you have any further queries.

Regards,

Nishanth Kulkarni