WEBENCH® Tools/ISOW7840: ISOW7840

Hi User6294349,

Thank you for posting to E2E!

ISOW78xx devices can withstand up to a maximum 15mA input current, and <4ma is recommended.

The 50kHz switching signal is expected to pass through the isolator as long as it is within recommended operating voltages, but please allow our team to confirm this and follow up with you during business hours M-F.

Thank you,

Manuel Chavez

Hi,

Like Manuel mentioned, 50kHz signal shouldn't have any issues in passing through the data channels of ISOW7840 as the device supports datarate upto 100Mbps.

Please note that ISOW7840 is a digital isolator with integrated power where the data channels only accept digital CMOS voltage inputs. The data channels have high input impedance and do not consume any current more than >10µA. When you apply the 50kHz voltage signal to ISOW data channels, the output of data channels on the isolated side reflect the input accurately without consuming much current at the inputs.

Like Manuel already mentioned, the data channel outputs support a max of 4mA drive current which is more than sufficient for CMOS digital input ports of other digital devices (like MCU). Let me know if this answers your question, thank you.

Regards,
Koteshwar Rao

H,

You say that data output support 4ma drive current but isolator has 130ma supply output current and safety limiting values are 400ma for 5.5V signals. I don't think ISOW can consume some currents. My exact question, Is the mentioned gate pulse pass the ISOW7840 or what do you suggest me for a gate pulse signal isolation? 

Thanks.

Hi,

Thanks for your response and sharing additional information.

Please allow me to describe more about ISOW and try answer your question. ISOW7840 is a device that has both digital isolation channels (which isolates digital data signals) and DC/DC isolated power supply (which isolates input power to provide isolated output power). This information is reflected in the image below from datasheet first image.

The data channels are named INA, INB, INC & IND where as the respective outputs are OUTA, OUTB, OUTC & OUTD. These channels only digital CMOS inputs and output digital CMOS outputs whose output can be either 3.3V or 5V based on the output chosen and can supply a max of 2mA for 3.3V and 4mA for 5V operating conditions.

The isolated DC/DC converter will isolate the input power to provide an isolated output which can be configured to either 3.3V or 5V. The DC/DC converter being a power supply can definitely support higher currents. The output currents supported by the DC/DC converter are specified in datasheet for different input/output voltage configurations as listed below.

1. 5V to 5V and 5V to 3.3V; Available load current >130mA
2. 3.3V to 3.3V; Available load current >75mA

I see you are trying to isolate a gate pulse train and your question is whether ISOW7840 can isolated and pass these gate pulses. The answer is yes, ISOW7840 can certainly isolate and pass the gate pulse train. Do you also need the ISOW7840 to drive a gate of high current MOSFET? No, ISOW7840 cannot do that.

I am not completely clear about your application and your requirement. If you can explain more about your application requirement and the need to isolate the signal then we would be in better position to recommend a suitable solution. If your requirement is to isolate a gate drive signal and drive a MOSFET/IGBT then ISOW7840 cannot do that. TI has isolated gate driver devices as well which are meant to isolate an input logic signal and drive a MOSFET/IGBT.

Please do let us know your requirement and we can suggest you a right device accordingly. Thanks.

Regards,
Koteshwar Rao

Thank you for explanations. I must use isolated gate driver devices. I added attachment my pulses voltage and current waveforms.(5V,400-500ma pulse current, max. 25ns propagation delay, max.50kHz switching frequency) Do you suggest me any isolated gate driver and is these drivers include isolated dc-dc source?

Hi,

Thank you for the confirmation. I will notify the isolated gate driver team about your question and they will be able to help you with suitable device suggestion. Thanks.

Regards,
Koteshwar Rao