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Neeraj , 01-12-2025, 09:02 AM

I have a circuit where I'm using a voltage divider to step down 60VDC to 3.483VDC (Required 3.3) because it will connect with MCU port to read the input. However, I’m concerned about potential heating issues, and if one of the resistors fails, it could damage the entire board. I’ve tried searching for a PMIC to handle this, but I haven’t been able to find one. Can anyone please help with suggestions? @Robert Feranec, could you provide some advice? This is the circuit in ESC board which I am designing from YouTube video and in video it was this voltage divider but I want something reliable because this solution not looking good.

SirJames , 01-12-2025, 11:00 AM

Well, if you are worried about wattage of resistors, you can always put two with half resistance in series or use resistor in bigger package (and higher power rating). You can also add clamping low leakage schottky between AN_IN and Vcc of MCU.

SirJames , 01-12-2025, 11:02 AM

If your analog input has 3.3V input range, why is your divider set to output 3.483VDC at 60V input? You dont want to measure voltage over 56.85V?

Robert Feranec , 01-12-2025, 12:45 PM

maybe you can use resistors with high values so a very low current flows through the divider?

QDrives , 01-12-2025, 07:53 PM

For supply voltage measurement I have always used a 150k (0603 or bigger, with max **working** voltage of >= 75V) on the high side and with 8.2k on the low side you get just over 63V as the absolute limit for 3.3V.
Add a diode. such as BAT54, to the analog supply like @SirJames also mentioned.

Neeraj , 01-15-2025, 02:09 PM

Hi,

I changed this configuration... It's 3V3 now... Btw thanks for your help.

Can you suggest where to add diode?

SirJames , 01-15-2025, 04:12 PM

Resistor R2 already limits current through schottky diode when overvoltage (or negative voltage) appears on VIN

SirJames , 01-15-2025, 04:19 PM

I recommend to set it little bit higher than 60V -> 3V3. For example 66V is 20x3.3. Easier math and you have room to read that there is a overvoltage.

QDrives , 01-15-2025, 08:15 PM

The 'math' may be 'easier', but you need resistor which are in defined ranges (E12, E24, E48, E96 or E192).

Vin = (ADC_in * Vadc_max * (Rhi+Rlo)/Rlo / ADC_max)
And since Vadc_max * (Rhi+Rlo)/Rlo / ADC_max is a constant (usually) and ADC_max is a 2^n, you can multiply with a constant and bit shift for the answer if using integers.

SirJames , 01-15-2025, 09:04 PM

You are correct. I use this TI online voltage divider calculator with resistors suggestion https://www.ti.com/download/kbase/volt/volt_div3.htm