Is Low-Voltage Dual Serial Motor Controller really 5A?

I am surprised that Pololu Low-Voltage Dual Serial Motor Controller can really drive motors with up to 5A continuous current. This is on par with L298 chip which takes way more space and gets hot when running.
Could someone please confirm the current rating?
What is the name of the circuit so I can look-up the datasheet?
Can I use this controller with 9V motors?
ref: https://www.pololu.com/catalog/product/120

Hello,

The low-voltage dual motor controller is way better than “on par with L298”, which delivers less than half the current. Our controller has discrete H-bridges that are MOSFET based, not BJT-based like the L298. Therefore, you get total on-resistance in the 80 mohm range, which translates to only 0.4 V loss at 5 A. On the L298, you lose something like 4 V by the time you’re drawing 2 A, which means 8 W (per channel). Our controller only has to dissipate 2 W even at 5 A. Of course, that’ll still get it really hot, and there’s no thermal shutdown, so it’s up to you to keep the current under the limit.

5 A is not that uncommon lately: if you do a search at Digi-Key for complementary MOSFET pairs in an 8-pin SOIC, you’ll see hundreds of options. An example is the Fairchild FDS8958A.

The motor controller’s limit is 7 V (a 5-cell NiCd or NiMH pack). If your 9 V motors give you enough performance at 7 V or less, you could use this controller. We’ve seen it running at up to 10 V, but that will put it out of spec. on several of the components so you would have to do so at your own risk. If you must have operation past 7 V, I recommend either the VNH2SP30 or the MC33887 motor drivers if you want to supply your own control signals or the TReX or TReX Jr if you want a complete dual serial motor controller for higher currents and voltages.

- Jan

Jan,

Thank you for the quick reply.
I am glad that you use more advanced components compared to my current L298-based driver.

I went to check the electrical rating on MOSFETs (http://www.fairchildsemi.com/ds/FD%2FFDS8958A.pdf) and found that they can take up to 20V. The MA3238C chip does not touch the motor voltage. So where exactly is it going beyond specs?
I am currently in Russia and can not get another controller fast enough. So it is crucial for me to understand whether I can feed it with 7 NiMH cells.

In that case, I recommend that you don’t use the low-voltage controller and instead consider the other units I mentioned. The other chip does get affected by the motor voltage, and anything past 7 volts definitely takes some voltages out of spec. Also, a 7-cell battery well charged can give you more like 10 V, so that really is past what this controller is designed for.

- Jan

Jan,

Could you publish the schematics for the controller? I want to better understand what happens with higher supply voltage.

Thanks!

Sorry, we don’t want to show the schematic. It would be of limited use to you in this case, anyway, since the motor supply gets connected to the MAX3238 chip, and the 7V limitation is there. I tried to get some extra characterization of the pin from TI, but they weren’t interested in encouraging any use of the part beyond its datasheet specs.

- Jan