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Using higher voltages for LTC2954 with voltage dividers

Thread Summary

The user seeks a pushbutton system for an 8s battery-powered motor (33.6V) to prevent accidental on/off presses, considering the LTC2944. The final answer suggests using an active transistor-based clamp with a zener diode to safely reduce the voltage to the chip's operating range, with options for either a MOSFET or BJT. The clamp imposes a voltage penalty and requires careful selection of resistor values to minimize current leakage.
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Category: Hardware
Product Number: LTC2954

Hello, newbie here and first time posting in this forum. So, sorry in here if there are any mistakes.

I was planning to implement a pushbutton system for our motor where you accidentally cannot turn it on/off by accidental presses.

it seems ltc2944 gives me the exact design I want where I can hold down the button for a couple of seconds before the motor turns on or off.

The problem is our motor runs off of an 8s battery where the voltage reaches 33.6V, significantly above the safe operating voltage of the ltc2954 chip.

My initial draft is just a direct connection but I am certain this will damage the chip:

As such, I was thinking if using a voltage divider would be suitable and what values of resistors would you suggest to make sure we don't have a significant amount of current leaking to the ground from the divider while also ensuring the chip functions normally?

This is a divider idea that I am thinking of right now:

Any solutions regarding this would help me a lot. Thanks.

  • Here's an active transistor-based clamp I've seen used in the past. The maximum voltage is set by the zener diode plus the transistor turn-on voltage. The clamp will also impose a voltage penalty even when the main supply is below the zener voltage.

    You can use either a MOSFET or a BJT. They have pros and cons of each. I usually see BJTs due to the lower forward voltage, but then you will need to increase the resistor-zener bias current due to the BJT base current. A MOSFET has a higher and more-variable forward voltage, but the resistor-zener current can be very small.

  • Thank you so much. Your solution is perfect and allows me to implement it in a small board size with as low BOM as possible.

    Thank you again.