HIP4080A H-Bridge driver bootstrap diode

[fuper]

Hey all -

I've been reading the data sheet for the HIP4080A https://www.electro-tech-online.com/custompdfs/2010/04/an9404.pdf I discovered this chip when reading about high current motor controlling from a nice article from nuts and volts: https://www.electro-tech-online.com/custompdfs/2010/04/nv52.pdf

I think I understand everything except the charge pump diode. It's value is not specified and I think its characteristics are "assumed" when dealing with mosfet charge pump stuff of which I have no prior experience with. This would be diodes CR1 and CR2 in figure 12 of the data sheet. The nuts and volts article shows them in their sample schematic but neglects to specify what they are [Figure 52.3 of the nuts and volts article].

Thanks!

 

[shortbus=]

On page 5 of the Parallax PDF it tells the values of the diodes and the capacitors. It calls them C3 and C4;

"Component selection for the HIP4081A is relatively simple. I selected the Harris
HRF3205 MOSFET which has an Rdson of about eight milli-ohms (0.008 ohms) for the
four H-bridge switches. The charge-pump diodes selected were from Digi-Key, but
virtually any 60V Schottky diode would work for this application. The charge-pump
capacitor (C3,C4) should be at least 10 times the input capacitance of your MOSFET.
The HRF3205 has an input capacitance of 4000pF. I used 0.22uF capacitors, which are
oversized but worked fine."

 

[fuper]

The other diodes

Ah I misspoke! There are other diodes in the diagram that are labeled CR1 and CR2. Those are the ones I am trying to figure out [I thought they were for the charge pump but I misunderstood]

On page 5 of the Parallax PDF it tells the values of the diodes and the capacitors. It calls them C3 and C4;

"Component selection for the HIP4081A is relatively simple. I selected the Harris
HRF3205 MOSFET which has an Rdson of about eight milli-ohms (0.008 ohms) for the
four H-bridge switches. The charge-pump diodes selected were from Digi-Key, but
virtually any 60V Schottky diode would work for this application. The charge-pump
capacitor (C3,C4) should be at least 10 times the input capacitance of your MOSFET.
The HRF3205 has an input capacitance of 4000pF. I used 0.22uF capacitors, which are
oversized but worked fine."

 

[mneary]

Ah I misspoke! There are other diodes in the diagram that are labeled CR1 and CR2. Those are the ones I am trying to figure out [I thought they were for the charge pump but I misunderstood]

Which diagram? Figure 52.3? No CR1 and CR2 here. Only one set of diodes CR1 and CR2 in Figure 12 of the intersil data sheet. Do you mean D2 and D3? They are for the charge pump. Just drawn slightly differently.

 

[fuper]

Which diagram? Figure 52.3? No CR1 and CR2 here. Only one set of diodes CR1 and CR2 in Figure 12 of the intersil data sheet. Do you mean D2 and D3? They are for the charge pump. Just drawn slightly differently.

Ahhhh crap thanks mneary. I see the charge pump diodes are specified in figure 52.3 They are D2 and D3 and are both B160DICT. Those are CR1 and CR2 from the data sheet Don't know why I didn't see that.

Can I trouble you with one more question? What is the purpose of the 4 diodes attached to each mosfet? I thought they were flybacks but I've not seen them connected in that way before [usually from drain to source]. Are they there to protect the mosfet gate from too high a voltage? Figure 12 of the data sheet does not show them there [but does show what I believe are the flybacks]

 

[mneary]

In Figure 52.3 the diodes D4, 5, 6, and 7 are Zener diodes and yes they do protect the gates from too high a voltage.

In Figure 12 of the data sheet shows diodes across Q1, 2, 3, and 4. MOSFETs have internal (intrinsic) diodes in those locations. Some people draw MOSFETs without them, but they are always there. Coincidentally this is the same place in the circuit where you would put flyback diodes. In many cases they are strong enough for flyback protection. Many conservative designers don't trust them and add their own diodes.

 

[fuper]

Thanks very much for walking me through this ! Very informative.

Thanks again!

 

[jgeidl]

A little more help will be appreciated.

Could you guys help a real novice with a part number for the diodes?

Thanks,

Jim

On page 5 of the Parallax PDF it tells the values of the diodes and the capacitors. It calls them C3 and C4;

"Component selection for the HIP4081A is relatively simple. I selected the Harris
HRF3205 MOSFET which has an Rdson of about eight milli-ohms (0.008 ohms) for the
four H-bridge switches. The charge-pump diodes selected were from Digi-Key, but
virtually any 60V Schottky diode would work for this application. The charge-pump
capacitor (C3,C4) should be at least 10 times the input capacitance of your MOSFET.
The HRF3205 has an input capacitance of 4000pF. I used 0.22uF capacitors, which are
oversized but worked fine."