H driver Layout issue

Hi,

I am designing the PCB for the H bridge (HIP4081A). It will be interfaced to the Micro. The H bridge is driving an inductive load. The micro is driving the H bridge with the Pulse width modulation waveform of frequency 100 KHz. The H bridge is driving the four N Type MOSFETS. The power supply for the H bridge is 12 volts and the 3.3 volts for the microprocessor.

What important layout rules should I implement inorder to protect the micro. from HIP 4081 A noise or noise introduced by switching of the transistors.

Thanks

John

Reply to
john1987
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Some more questions are as follows

  1. How should I choose the by pass capacitor for the HIP and micro?

  1. what are the best techniques to stop the noise coming from the swicthing of the transistors to not to reach the HIP 4081 chip

Reply to
john1987

I was troubleshooting a board like this today. (It turned out the problem was with the motor not the PCB.) Despite just having 2 layers, and the circuit being split across 2 PCB's, and breaking just about every EMC rule, it still worked. There was a cheap 100uF decoupling capacitor for the H Bridge driver IC. It radiated a heck of a lot of noise and would not pass any kind of formal EMC test, but the circuitry seemed pretty robust. What I'm saying is, modern digital circuitry is pretty resilient when you operate at frequencies as low as 100kHz.

The circuit was driving the motor with about 0.3 amps at 24V. EMC performance would have been hugely improved by the addition of an earth plane, but if you cannot afford an extra plane, do not worry too much. The driver ICs' datasheets usually have several notes about layout.

Reply to
Nemo

I have blown out mosfets in h-bridges driving motors. It has to do with forward biasing the fet substrate diodes, then snapping them in reverse when the bridge switches. The step-recovery transient can blow out the gates. I don't know if certain fets are better in this respect. I fixed it with power schottkies.

John

Reply to
John Larkin

That is very low voltage and current; it is hard to get it wrong.

The consumer electronic stuff is laid out in one, maximum in two layers. Extra layer = extra cost. It passes the EMC tests, too.

That tells about FET turn on set way too fast.

It takes pretty healthy shottkies to divert the current from the body diodes. That complicates the layout and increases the price.

Vladimir Vassilevsky DSP and Mixed Signal Design Consultant

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Reply to
Vladimir Vassilevsky

Rule #1: Make it absolutely sure that under no circumstances the MCU could drive open both FETs in a switching leg. Pay special attention to the startup/shutdown situations and the power supply sequencing.

Vladimir Vassilevsky DSP and Mixed Signal Design Consultant

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Reply to
Vladimir Vassilevsky

I'd like to stress I didn't design it 8)

Reply to
Nemo

I was under the impressoin that while this is true (diverting current from the body diodes is hard), the body dioes are also rather slow, and therefore the Schottkies take up the slack immediately after turn-off... even if they themselves then end up turning off in pretty short order as well. (Which implies that they can be sized for only having to handle the total current for a relatively small duty cycle...?)

Reply to
Joel Koltner

Some of us H-bridge designers have been known to implement active clamping to avoid body diode conduction ;-) ...Jim Thompson

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| James E.Thompson, CTO                            |    mens     |
| Analog Innovations, Inc.                         |     et      |
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Reply to
Jim Thompson

A Shottky has to defeat the forward conduction of the body diode; it takes similar size Shottky even in the static situation. This is further complicated by the stray inductance. The turn-on of a body diode is instant; that is forced turn-off which causes problems.

Vladimir Vassilevsky DSP and Mixed Signal Design Consultant

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Reply to
Vladimir Vassilevsky

I believe hip4081a has internal logic that prevents the upper fet from turning on when the lower is on

-Lasse

Reply to
langwadt

I'd have used IGBTs

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Reply to
Fred Abse

How did you fix this with power schottkies. Can you give a detail example. I am using IRF40 transistors to drive an inductor coil.

John

Reply to
john1987

I did a power H-bridge a while ago, but voltages were high enough that Schottky diodes could not be used. I did find some ULTRA-fast junction diodes that did fine. While testing, I was amazed to see how SLOW the turn-on of the body diodes was. I could put 12 V forward (for the diodes) across them for a number of microseconds before conduction started. This was with that leg of the bridge sourcing over 10 A to the load inductance, so when the low-side transistor shut off, the output terminal went below ground. The fast diode and a snubber circuit to carry the current until the fast diode could turn on fixed the problem.

Jon

Reply to
Jon Elson

Slow body diodes is why active clamping is so easy to implement (at least monolithically).

I've been doing it for many years for single-ended loads, like relays. This year is the first time I've done it for H-bridges. ...Jim Thompson

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| James E.Thompson, CTO                            |    mens     |
| Analog Innovations, Inc.                         |     et      |
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Reply to
Jim Thompson

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