How to pick up a electromagnetic coil control board?

Another suggestion is to use a single channel high-side switch controller with current limiting MAX14922.pdf (analog.com). In this case, you should select the external sense resistor, MOSFET and TVS.

Hi YuriyK1,

Thanks a lot for the detailed explain, and I have another question if you would like to provide any suggestion. 

In my application, I may only pass 3A for a short pulse (~10ms) then switch it off for long period 100ms, and repeat the cycle multiple times. In this case, the average current amount is still low but the peak current will be high. Do you think MAX14916 can manage this? Or should I stop looking for high frequency switches and start looking for some current charging and firing circuit?

Thanks for your time,

Nianyu Jiang

In both cases, with the MAX14912 or MAX14916, the peak current of 3A exceeds the max current limits. The DO switch will/may go to thermal shutdown due to overheating. It is hard to predict when the thermal shutdown can occur because it also depends on ambient and die temperature. Is the peak current of 3A limited only by the coil impedance? How are you going (prefer) to control the switching frequency, using the SPI or input pin? How many DO channels do you need? 
In any cases, the 3A of peak current will not break the part, but knowing application details allows suggesting a better solution. 

In both cases, with the MAX14912 or MAX14916, the peak current of 3A exceeds the max current limits. The DO switch will/may go to thermal shutdown due to overheating. It is hard to predict when the thermal shutdown can occur because it also depends on ambient and die temperature. Is the peak current of 3A limited only by the coil impedance? How are you going (prefer) to control the switching frequency, using the SPI or input pin? How many DO channels do you need? 
In any cases, the 3A of peak current will not break the part, but knowing application details allows suggesting a better solution. 

Hi YuriyK1,

Thanks for the explain. This is an early study about generating magnetic field for an engineering project. We are ultimately trying to generate a 0.5T magnetic field using a coil (I am now using a adafruit electromagnet) with a on/off frequency at 10~1k Hz. 3A is the minimum current I calculated for the flux density, I may need to further increase the current up to 10A if necessary.

I am not an expert at inductive load control and thats what I am trying to do: I prefer to use a PWM signal (input pin from microcontroller or wave generator), to switch on/off the device, which means I need at least a digital controlled switch and a inductive load driver with protection (correct me if I am wrong). We currently need only 1 channel but in future we aim at 6~8. I learned that switching inductive load (especially at high frequency) will need specific care for the reverse voltage when shut off and thats why I am trying to find a well-designed driving circuit.

Based on the info, could you please give me some suggestions on what types of product should I aim for?

Appreciate your time and help!

Nianyu Jiang

Okay, you are going to control the magnetic field by controlling time of the current flow (PWM) through the coil. In this case, the MAX14900E fits better for your purposes. You are going to use parallel mode to control the output(s) through the IN_ pins. You will be using the MAX14900E under short circuit conditions, but it is okay since this is an engineering project. The MAX14900E EVKIT (MAX14900DEVBRD) is available on the DigiKey website https://www.digikey.com/en/products/detail/analog-devices-inc-maxim-integrated/MAX14900DEVBRD/5880608 and it does not need any modifications. In high-side mode, multiple outputs can be connected together in parallel to achieve higher load currents. 

Hi Yuriy,

Thanks for this suggestion! I will give a look at the datasheet and consider the 14900E.

Appreciate your help so much!

Nianyu Jiang

Hi Yuriy,

Thanks for the information, the MAX14900E looks exactly what I need for a quick setup and project test. I have one more question by reviewing the datasheet. Suppose I am using the parallel mode by combining 4 output, does the current limit simply increase 4 times? or it can be calculated by some equations?

Nianyu Jiang

Hi Nianyu Jiang,

The current limit is for channel bases, and it does not change. When you are paralleling the output channels, the current will be spread between them approximately evenly and that allow to drive a higher total current. However, the channel's impedance is not equal and if the current through the channel reaches the limit, that channel may shuts off due to channel thermal shutdown. This can lead to cascading shuts of other channels. You should carefully select the number of paralleled channels based on the total current.

Regards,

Yuriy

Hi Yuriy,

I have got the MAX14900E at my hand and ready for test. To my best understanding, the current limit (2A) is per-channel. I was trying to use high-side mode and paralleled 4 output channel together under short circuit condition. The coil resistance is 10 Ohm, and I suppose if I use a power source of 20V, I create 2A at each channel. If I choose the set power source limit as +20V 8A, does it meet my requirement of passing the maximum current into the coil? I would like to figure this out before I maximize the current input.

Thanks,

Nianyu Jiang

Hi Nianyu Jiang,

If the coil resistance is 10 Ohm and supply voltage is 20V, the max current through the coil is 2A total (not at each channel). In this case 8A supply current limit will never be reached and it is safe to use maximum current limit. Do I miss something? If you trying to reach total current of 8A, the coil resistance should be 20V/8A= 2.5Ohm or you can put 4 coils in parallel. I suggest starting with one coil and then increasing number of coils to reach maximum magnetic field power. 

Regards,

Yuriy

oh I think now I understand the parallel mode which is distributing current not voltage. Thanks for your explain! I will give a try first and then see if I can make any improvement.

Nianyu Jiang

Hi Yuriy,

We have tested the board which works fine. The board has the maximum voltage supply of 36V, considering our circuits is of 12 Ohm resistance, the current is at maximum 3A.

The magnetic coil, under 3A current, reached the magnetic flux density at what we expected. However, we intend to safely operate the coil at higher current for our project purposes. We are trying to find a similar board which can allow 120V, 10A (roughly). Is there any product that you can suggest?

Thanks for your help!

Nianyu Jiang

Hi Nianyu Jiang,

I'm glad that you are able to reach your goal using the MAX14900E evkit. Unfortunately, we don't have devices that can support 120V, 10A, and safety requirements. The maximum operating voltage for the DO family is 36V. You will need to design such circuitry using discrete components. 

Best Regards,

Yuriy