ISOW7840: Can i use 5V DC input to ISOW7840 IC and pin 4 and pin 5 of this IC connected as input to a Microcontroller pin which is operating at 3.0 VDC .

Harish Gode

Part Number: ISOW7840

Hi,

I am evaluating TI ISOW7840 for my application .

The Query is Input side is 5V and 3V which are currently Isolated. If I short the grounds then I can give 5V or 3V as input and output is always 3.3V DC in ISO7840 IC. The efficiency is around 43% . If I use 5V input the input current will be less for same output power.

But I want to connect pin 4 and 5 which are digital input to a Microcontroller which as Vcc of 3.0 V DC. Can i use 5V DC input to ISOW7840 IC and pin 4 and pin 5 of this IC connected as input to a Microcontroller pin which is operating at 3.0 VDC . The output of this IC is be 3.3V DC only for both 5V or 3V DC inputs.

Regards

Harish

over 5 years ago

0 Koteshwar Rao over 5 years ago

TI__Mastermind 49415 points

Hi Harish,

Thank you for showing your interest in ISOW7840 for your application.

As stated in Section 7.3 of ISOW7840 datasheet on Page 6 titled "Recommended Operating Conditions", the recommended digital input voltage levels are supply dependent. VIHmin is about 0.7*VSI whereas VILmax is 0.3*VSI, where VSI is the input side power supply voltage. Hence applying 3V input signals when VSI is 5V will violate the recommend operating conditions and device will not identify the input signals accurately.

To be specific to your application, applying 3V logic signals from MCU to INA, INB, INC & IND when VCC of ISOW7840 is 5V is going to violate datasheet requirements. Hence this shouldn't be done. Thanks.

Regards,
Koteshwar Rao

0 Harish Gode over 5 years ago in reply to Koteshwar Rao

Prodigy 50 points

Hi Koteshwar,

I got yesterday reply from TI that i can connect microcontroller operating at 3.0VDC to ISOW7840 with input voltage of 5V DC. Please see attached file.

So i am confused.

1) It means i have to give 3.0V DC as input to DC DC converter input and output will be 3.3V DC . In this case the efficiency will be impacted.

2) The GND1 pin 2 and pin 8 should have a common GND or can be of different GND for DC DC converter circuit ( pin 1, 2) and Digital input circuit ( pin 3 to Pin 8) .

TI_ISOW7840.docx

0 Koteshwar Rao over 5 years ago in reply to Harish Gode

TI__Mastermind 49415 points

Hi Harish,

Apologies for the confusion, the response that I have posted earlier on this page is the correct response.

Please find below my inputs to your follow-up questions,

1. I understand your concern here, unfortunately the logic input levels should match its respective supply voltage levels for device ISOW. Alternatively, you could also use a 3V to 5V level translator between MCU & ISOW to be able to use ISOW with 5V supply on VCC.

2. Pin 2 and Pin 8 of ISOW7840 are already internally connected to each other. Though the device is going to function fine even if you use only one of them, we strongly recommend the two GNDs to be connected to each other externally for better overall performance. It also helps in PCB routing most of the time.

Thanks.

Regards,
Koteshwar Rao

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ISOW7840: Can i use 5V DC input to ISOW7840 IC and pin 4 and pin 5 of this IC connected as input to a Microcontroller pin which is operating at 3.0 VDC .