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I have two chips and I would like the logic out of one chip to control the chip enable pins of another chip. I am just not sure how to do it.

I have a chip with an output of 3.6v with logic on and -1.65v with logic off on pin 7. The chip is MAX913CPA+

I have another chip UCC27424P that has 2 enable pins, pins 1 and 8. That on the data sheet states min -0.6v to max 15.3v. It also states they are internally pulled up to Vdd with 100kΩ resistor for active high operation, does this mean something connected to the enable pins will see Vdd when its initially enabled with 3.6v? The data sheet indicates it would enable at TYP 2.4v MAX 2.9v and disable at TYP 1.8v MAX 2.2v

Could I get away with directly connecting the two chips or is the -1.65v logic off a real problem? Now the max on the state changes indicates 2.9v but else where on the data sheet it indicates max vdd+0.3v so 15.3v volts? Do I really need to be concerned with 3.6v exceeding 2.9v?

Is there something simple I can do to make -1.65v be ground 0 but leave the high end go to 3.6v? I do need fairly fast switching 300kHz.

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  • \$\begingroup\$ Where in the MAX913 datasheet did you see -1.65V. In don't see that number anywhere. \$\endgroup\$
    – user4574
    May 5, 2022 at 1:48
  • \$\begingroup\$ The MAX912/913 has TTL outputs. A Low output will be between 0 and 0.4 V, while a High will be between 2.4 and 5.0 V. \$\endgroup\$ May 5, 2022 at 1:57
  • \$\begingroup\$ The -1.65v is what I measure between the MAX913 chip pin 7 and ground when its logic off and the 3.6v is what I measure between pin 7 and ground when its logic on. \$\endgroup\$
    – axawire
    May 5, 2022 at 2:00

1 Answer 1

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From what I can read on page 2 of the MAX913 datasheet, the Low output value is a maximum of 0.5V (not -1.6v) and output +3.4V. Furthermore, And on page 4 of the UCC27424P, the Enable pin voltage range is -0.3 to 6V up to VDD+0.3V

As far as the pull-up resistor, it only means that if you bring pin 1 or 8 to ground, the chip will source a small current in the order of (+15V/100k) 150uA, which is of no concern for your MAX913.

Conclusion: you have nothing to be worried about as far as absolute maximum is concerned.

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