Macspice voltage divider code4/1/2023 So I assume I have a issue in relation to the adc input impedance here, I read the section "45.7.2.1 Track and Hold Time versus Source Output Impedance" of the datesheet but I don't get how can I apply those values to understand what I have to do to calculate this in the proper way Here is a table with the values from the 10 + 1 voltage divider, the 100 + 10 are very similar and the 4.7 + 1 is better in the relation that the diference from the lower and the higher gain is lower (5.1 to 5.738). But on my test I need to set it as low as 7.5 to measure a input voltage of 0.5v and as high I go I need to make the Gain bigger and bigger even above the 11 that I calculate. The problem I'm having is that the Gain multiplier that I have to use is not a fixed value.įor example in the 100 + 10 or 10 + 1 the Gain is around 11 (I have properly mesure the resistor to make shore what the real value is on my case 10.985). The maximum voltage in this case is 12v but I wanna to use up to 18v. I have tested 3 combination of voltage divider, 100k + 10K, 10k + 1K and 4.7k + 1K I have set 6 adc ports to read the same input, in order to have a more accurate measure. I'm calling the "Gain bug", the Gain or the multiplier that is used to correct the measure voltage from the voltage divider. Read the bellow to understand the problem. What are the recommended values for the DUE? But high value resistors also protects the circuits effectively.How do I take in consideration the "adc input impedance" to proper mesure the voltage on a voltage divider? Linear Voltage Regulators also offer additional protections that you may want to consider. If your source voltage is constant and regulated, a divider is ok. If the input voltage is higher, the output voltage will also be higher, proportionally, with a divider. The main difference between a voltage divider circuit made off two resistors and a Linear Voltage Regulator (LDO or non-LDO) is that the Linear Voltage Regulator will always output the same voltage regardless of the input voltage whereas the resistor divider will only divide, not regulate the voltage. The total value between source to ground defines the power loss. In the case of signal input, in order to limit current consumption, use high value resistors in your voltage divider: 22K or more. If the goal is to provide a 3V signal to an ic input, it's also fine since it consumes very little. In another example, using a voltage divider circuit or a Linear Voltage Regulator when you need to convert 5V to 3V for an application consuming more less 100mA is fine. With a 20V difference, even 100mA can generate enough power dissipation to consider using a step-down regulator. I was wondering whether there's any problem in using the divider instead of step-down regulator.Ī step-down regulator (Switching regulator) is better or required when the Power Dissipation using a voltage divider circuit or a Linear Voltage Regulator, is too high.įor example when you are powering a device from a much higher voltage source. I have never seen this or had to resort to it, so I suspect it is not commonly needed. An option (a bit odd, but potentially workable) would be to use a low quiescent current (Iq) linear regulator (possibly an LDO) to generate the 3.3V for the pullups. In micropower designs, the divider approach may not be the wisest option for that reason. Note that the divider will consume power even when SDA and SCL are not pulled down. Simulate this circuit – Schematic created using CircuitLab The effective pullup resistance is R1 in parallel with R2, which is (R1*R2)/(R1+R2). The effective pullup voltage is V * R2 / (R1+R2) where R1 is the upper leg of the divider and R2 is the lower leg of the divider. The basic answer is, yes, you can use a divider for pullup. In your application that would be the Raspberry Pi VCC, I guess.īut it is still an interesting question. The best option, when possible, especially in the case where there is a single I2C master, is to pull up to the same VCC as the I2C master.
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