Post History
It's been a while since I did 1-wire, so I don't remember the current levels. R18 seems rather high for supporting the minimum required voltage at the maximum possible current. Let's say for sake...
Answer
#1: Initial revision
by
Olin Lathrop
·
2024-03-11T12:19:42Z (8 months ago)
It's been a while since I did 1-wire, so I don't remember the current levels. R18 seems rather high for supporting the minimum required voltage at the maximum possible current. Let's say for sake of example that your 1-wire device is specified to work down to 2.0 V. You're already going to lose 300 mV or so thru D5. That leaves 3.0 V coming out of D5, so only allows 1 V drop across R18. With the value you have now, the maximum operating current the device can draw is (1 V)/(1.5 kΩ) = 667 µA. Are you sure your device can operate on that little? Another issue to consider is the current that will be dumped on the 3.3 V supply when OUT is externally driven to 36 V. Right now that is around 3.2 mA thru R23. There is no problem as long as you are always draining at least that from the 3.3 V supply internally. Also consider if 36 V could be present with this device off. What would that do to the internal 3.3 V supply? A dedicated Zener clamp might be in order.