Sensors and analog
Voltage divider
Work out what a resistor divider puts out, what it costs you in current, and whether an ADC can read it. Enter the supply and both resistors, or work backwards from the output voltage you want.
Mode
Enter the supply and both resistors to get the output.
Between the supply and the output.
Between the output and ground.
Output voltage
3.837V
32 % of the supply.
Divider current
816µA
Source impedance
3.2 kΩ
R1 dissipates
6.66 mW
R2 dissipates
3.13 mW
Caution
This divider will show up in a battery budget
The divider draws 816.3 µA continuously, and it draws it whether the node is awake or asleep. On a node whose sleep current is a few microamps, a permanently connected divider dominates the whole energy budget. Switch the divider with a MOSFET on the low side, or raise both resistors and buffer the output.
Battery life estimator
Why this matters
Most divider calculators stop at the output voltage, which is the part nobody gets wrong. The two things that actually break designs are further down. A divider built from megaohm resistors to save power presents an impedance the ADC sample and hold cannot charge through, and every reading comes back low with no obvious cause. A divider built from small resistors reads perfectly and quietly draws more current than the rest of the sleeping node put together, so a battery you sized for a year is flat in a month.
Assumptions and sources
- Ideal resistors at their marked value. A 5 % pair can shift the output ratio by several percent, which matters when the divider feeds a battery gauge.
- The load on the output draws no current. Any real load sits in parallel with R2 and pulls the output below the calculated figure.
- The 10 kΩ source impedance limit is a rule of thumb for microcontroller ADCs sampling at typical rates. Slower sampling tolerates more; check the datasheet for the figure your part gives.
- Power figures are steady state. A divider across a rail that spikes sees more than the steady state dissipation.