How to Find Current Draw of BU4811FVE Voltage Detector from Datasheet (1.8-3.6V)

Hello, I am a student in Computer Engineering and quite interested in Embedded system design and IOT. Currently, I am facing an issue regarding the datasheet reading and extracting the exact information.

I am using voltage detectors in a circuit and need to calculate the power consumption of the detector at each value of voltage between 1.8-3.6 volts. How, can I get the current draw in the detector depending upon the voltage. How to find it via datasheet?

Following is the link to datasheet:

https://www.rohm.com/datasheet/BU4811FVE/bu48xxg-e

I will be very grateful if you guide me through.

Fig 3 at the top left on page 6 has done the work for you, they have used the typical values in plotting the graph. As you will know, power consumption is current times voltage, so extract the current from the graph at  various voltages and compute the power.However, there are some issues, so read on.On page 5 a the top, there is a table with the data you need, IDD1 and IDD2 in uA against VDET. The current is different if the device is on or off, and it lists the currents for a variety of supply voltages, both typical and maximum. You will need to go through the  data sheet tables and calculate that product for each line.You need to take into account that there is a spread of current, typically a Poisson  distribution but not necessarily, it could be skewed towards the higher current end.  Without a graph it is hard to say, but assume that most units will be around the typical value, with a small number at the worst case value, which for low power users is obviously the critical end. One of the parts is open drain, the pull up load resistor needs to be large to keep the power supply current as low as possible when the output is "low". If  driving a CPU, then they often have programmable pull up resistors, but it may be lower than is desirable, check it and the CPU port input current and voltage constraints if  a processor is being used to ensure that the "high" and "low" input voltages are OK with the value of external pull up resistor.If you need to know precisely then you need to measure it, at the typical currents that is not easy. It is a good idea to always design for the worst case if you don't have any useful statistical information on the part. If it is lower then you are a winner as far as battery life is concerned. In most cases other components in the system will be drawing more power, CPUs and wireless chips in particular, but poor circuit design in any portion of a system can also cause problems where low power is concerned.Cheers,Richard

Then, if you can, activate the relay.  If the coil voltage is 230V be VERY careful, use insulated lugs if possible to minimise the risk of contact.  You should hear the relay operate and you should not find almost zero resistance between the two NO1 contacts, and also between the two NO2 contacts.
The large lug on the right looks like a mounting point and should not have any connection to any of the other contacts. mybkexperience.com

Any update for this ??? 

Thank you for the guidance, can I use the graphical values of current for now?  And does the current consumption changes with the variation in the frequency ranges of overall circuit? For example, if the circuit was initially working with 16MHz and then the frequency switches to 8Mhz. The current value for the MSP430 changes but does the current value for detectors also change?

No, they are totally independent of one another. The frequency you are talking about is the  internal clock rate for the micro, which only impacts on the micro's power consumptioncheers,Richard

Okkk. I got that. It means that the components other than micro-controllers (e.g detectors, regulators, etc) are not effected by the frequency variations. I was confused because I am using a regulator as well in the circuit which needs a capacitor and inductor for optimized functioning. So I thought may be the circuit current calculation requires frequency as in RLC circuits. Following is the datasheet for the regulator I am using. http://www.ti.com/lit/ds/symlink/tps62740.pdf
Question: One last thing, I am using the formula of power consumption by the regulator asP = (Vin - Vout)*Iout + (Vin*Iq)Where Iq is the quiescent current and Iout is output current which according to datasheet I took as 300mA for all voltages. Am I doing it correctly?

 What output voltage do you need, and what type of battery are you using on the input?Using a switching regulator,  Input power=output power/efficiency, which makes the regulator input look like a negative resistance, so the input power is very close to the output power over the working current and voltage range of the switcher used. This comes about because  the duty cycle of the switching changes as the input voltage  and load current change to maintain a constant voltage on the output. In practice, there is an efficiency  dependency based on  input and output voltage and  load current, which is quite apparent if you look at the graphs on pages 15 and 16. For example, it will change as the battery voltage on the input drops during discharge.What you have to do is calculate the power for the best and worst case input voltage and load current  to get a feel for the numbers. It could be that you can work with a 90% efficiency as a worst case, just looking at the graphs, and it will be close enough.From your comments, it is apparent that you do not understand switch mode power supplies, it would be a good idea to get a few tutorial articles off the web and study them before proceeding to the design stage. PCB layout is critical to the successful operation of a SMPS, read page 23 of the data sheet, Fig 53 on the same page shows the recommended layout.Cheers,Richard

Currently, I am simulating over matlab to get the idea of the energy consumption. I am providing voltage from the voltage traces and (starting from 3.5559 to 2.2220) At every voltage, the code decides the output voltage as for the input voltage between 3.6-3.3, output voltage is 3.3. Now, I need to calculate the power consumption within the regulator. For that, I considered 300mA as Iout and used the above formula of power dissipation.

The power consumption of the regulator is the difference between the power out and power in, which is most readily derived from the efficiency curves on the graphs. It is largely related to switching and core loses in the inductor. Modeling the switching regulator as a discrete device would be a waste of time, it will be too complex and not very accurate, so you will need to model it as a black box with  parameters obtained from the graphs in the data sheet. As I said, if the efficiency is considered to be 90% worst case (from the data sheet graphs)  and the output power is say 1W, then the input power is approx 1.1W, so the dissipated power is the difference of the two, and it will be very close to that value over the whole operating range of the regulator.Cheers,Richard

Hello, I am really grateful to have such a guide like you. I am moving forward in my project. As I had asked about the power consumption in the detectors and I shared the datasheet as well. I have drew some current values for various detectors I am going to use in my project. BU4918, BU4922, BU4928, BU4933. As I had a circuit current graph (performance curve) and the IDD1 values in the datasheet. considering the performance curve for bu4916 and the typical current values for various detectors, I drew the following performance curves for BU4918, BU4922, BU4928. Can you have a look if I have mapped it in right way. 

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