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Question first:

Is there a bootstrap driver that is available in DIP, works similar to the IRS2001, but is OK with a VCC of 4-5V? I'm also a bit limited in the amount of space I have -- is there a very small circuit that can do the bootstrapping for me with what I have available? Specifically, the switcharoo between charging the bootstrap capacitor, and then feeding it into the gate of the N-channel, is something I can't quite figure out how to do discretely.

Background:

I have a system with 5V logic switching a 5A motor at 1 kHz PWM frequency with a 6.4V-8.4V voltage. I'm building this myself, and am not set up to do surface mount circuits -- and most commercial H-bridge drivers for 5A want external switches anyway.

I built a H-bridge with power MOSFETS, P-channel high side, and N-channel low side, and using the 5V logic to switch the N-channel, and use a 70 Ohm pull-up and small signal N-channel to pull down the gate of the P-channel. At this PWM rate, that's good enough (220 Ohm pull-up was not -- the PWM blew the P-channel devices.) However, the loss of the 70 Ohm pull-up when pulling the gate down is significant.

I now want to use both high-side and low-side N-channels. I got some IRS2001pbf hi/low side drivers, which seemed like they would do the job -- except they have a "undervoltage lockout" feature that wants VCC to be at least 9V. This is to protect N-channel devices that want 10 V VGS -- but I'm using a IRLB8721pbf device with a 4.5V VGS RDSon of 18 milliohms, so I don't need that. I just need to bootstrap above the drive voltage of the motor by 4.5V to 5V.

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  • \$\begingroup\$ You do not need to bootstrap the voltage since demanded voltage is within the supply voltage. Have a look at the answer to this question. \$\endgroup\$ – abdullah kahraman Oct 21 '12 at 20:05
  • \$\begingroup\$ Ops. Sorry, after actually reading your question, I see that you want to use N Ch MOSFETs for both high and low side. \$\endgroup\$ – abdullah kahraman Oct 21 '12 at 20:08
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    \$\begingroup\$ Do you have room for a basic transistor bootstrap? \$\endgroup\$ – Vlad Oct 22 '12 at 7:07
  • \$\begingroup\$ I doubt that -- that needs the two transistor switcheroo, right? \$\endgroup\$ – Jon Watte Oct 22 '12 at 21:18
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So, the friendly folks at IR got back to me, and suggested I swap out the IRS2001 with a IRS2301. The IRS2301 has a VCC requirement of just under 5V, and will thus work for my application.

Now I just have to wait for the priority mail from Digi-Key...

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