level shifters and mosfet drivers

Tekko · 30th April 2006, 12:15 PM

If i use a MAX628 mosfet driver to a class d amp project, do i still need a level shifter on the high side input ?

If so, how is a level shifter made ?

fredos · 30th April 2006, 12:46 PM

Simply use a 6N137 optocoupler, but you will need a mosfet driver for each mosfet..

Fredos

www.d-amp.com

Tekko · 30th April 2006, 01:18 PM

The MAX628 is a dual mosfet driver, one inverting and one non inverting.

Could i use optocouplers from like a smps ?

fredos · 30th April 2006, 01:20 PM

Bad move with your IC...Use and inverting with the 6N137 and non-inverting with the lower side..

Fred

www.d-amp.com

Tekko · 30th April 2006, 01:26 PM

Hum ?

I don´t fully undterstand what you mean ?

What was a bad move ? Atleast the MAX628CPA IC´s are free samples.

fredos · 30th April 2006, 01:33 PM

You cannot drive upper and lower mosfet with that single chip, you will need 1 for upper mosfet and 1 for lower...If I understand that you was planning to use this chip for high side and lo side driver..

Fredos

Eva · 30th April 2006, 01:42 PM

As the datasheet makes obvious at first look, the ICs of that family (MAX626/627/628) are plain dual gate drivers, with both halves sharing the same power supply pins. Thus, there is no way in which you could drive a half-bridge-like class D output stage with one of these ICs.

Not only level shifting is required, but also independent or floating gate buffers are. You can either design a discrete solution, or use an IC having all those features built in, like IR2112, IR2110 or IR2113.

Also, there are standard and fast optocouplers like 6N137 whose practical propagation delay is in the range of 50ns. However, be very careful when using optocouplers because they don't provide perfect AC isolation but only DC isolation. There are internal capacitances between the input and the output sections of the IC that will disturb the state of the output if a certain common-mode dV/dt slope is exceeded during switching transients. You will find those dV/dt inmunity ratings on datasheets, and even in the best optocouplers from Avago (formerly Agilent or HP) the rated dV/dt (up to 15KV/us) may become quite short considering the fast rise and fall times involved in class D (expect something like 100V in 40ns or less). Indeed, I can tell that simple optocouplers like 4N25 are extremely easy to disturb.

I feel that you should learn more about switching circuits before starting class D experimentation, otherwise plenty of component blowing disasters may arise.

Tekko · 30th April 2006, 02:30 PM

Bah

Is it possible to cancel a samples order ?

Tekko · 30th April 2006, 02:37 PM

What about SC1205CS for mosfet drivers ?

Will they work ? The datasheet does say class d amplifiers.

Tho i have not found any place that sells them

Anyone have a few ?

fredos · 1st May 2006, 01:47 AM

Look good, but power supply limted to abou 18V if you use 12V bootstrap voltage...Good for experimentation!

fred

www.d-amp.com

30th April 2006, 12:15 PM	#1
Tekko diyAudio Member Join Date: Jan 2005	level shifters and mosfet drivers If i use a MAX628 mosfet driver to a class d amp project, do i still need a level shifter on the high side input ? If so, how is a level shifter made ?

30th April 2006, 01:42 PM	#7
Eva diyAudio Member Join Date: Oct 2003 Location: Near the sea	As the datasheet makes obvious at first look, the ICs of that family (MAX626/627/628) are plain dual gate drivers, with both halves sharing the same power supply pins. Thus, there is no way in which you could drive a half-bridge-like class D output stage with one of these ICs. Not only level shifting is required, but also independent or floating gate buffers are. You can either design a discrete solution, or use an IC having all those features built in, like IR2112, IR2110 or IR2113. Also, there are standard and fast optocouplers like 6N137 whose practical propagation delay is in the range of 50ns. However, be very careful when using optocouplers because they don't provide perfect AC isolation but only DC isolation. There are internal capacitances between the input and the output sections of the IC that will disturb the state of the output if a certain common-mode dV/dt slope is exceeded during switching transients. You will find those dV/dt inmunity ratings on datasheets, and even in the best optocouplers from Avago (formerly Agilent or HP) the rated dV/dt (up to 15KV/us) may become quite short considering the fast rise and fall times involved in class D (expect something like 100V in 40ns or less). Indeed, I can tell that simple optocouplers like 4N25 are extremely easy to disturb. I feel that you should learn more about switching circuits before starting class D experimentation, otherwise plenty of component blowing disasters may arise. __________________ I use to feel like the small child in The Emperor's New Clothes tale

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30th April 2006, 12:46 PM	#2
fredos diyAudio Member Join Date: Mar 2005 Location: Quebec	Simply use a 6N137 optocoupler, but you will need a mosfet driver for each mosfet.. Fredos www.d-amp.com

30th April 2006, 01:18 PM	#3
Tekko diyAudio Member Join Date: Jan 2005	The MAX628 is a dual mosfet driver, one inverting and one non inverting. Could i use optocouplers from like a smps ?

30th April 2006, 01:20 PM	#4
fredos diyAudio Member Join Date: Mar 2005 Location: Quebec	Bad move with your IC...Use and inverting with the 6N137 and non-inverting with the lower side.. Fred www.d-amp.com

30th April 2006, 01:26 PM	#5
Tekko diyAudio Member Join Date: Jan 2005	Hum ? I don´t fully undterstand what you mean ? What was a bad move ? Atleast the MAX628CPA IC´s are free samples.

30th April 2006, 01:33 PM	#6
fredos diyAudio Member Join Date: Mar 2005 Location: Quebec	You cannot drive upper and lower mosfet with that single chip, you will need 1 for upper mosfet and 1 for lower...If I understand that you was planning to use this chip for high side and lo side driver.. Fredos

30th April 2006, 02:30 PM	#8
Tekko diyAudio Member Join Date: Jan 2005	Bah Is it possible to cancel a samples order ?

30th April 2006, 02:37 PM	#9
Tekko diyAudio Member Join Date: Jan 2005	What about SC1205CS for mosfet drivers ? Will they work ? The datasheet does say class d amplifiers. Tho i have not found any place that sells them Anyone have a few ?

1st May 2006, 01:47 AM	#10
fredos diyAudio Member Join Date: Mar 2005 Location: Quebec	Look good, but power supply limted to abou 18V if you use 12V bootstrap voltage...Good for experimentation! fred www.d-amp.com

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