How to calculate the quiescent current with the Datasheet given values. Example MP3429 Boost converter.
IQ= 25uA at VIN and IQ=550uA at VOUT.
If the DC/DC Boost have 3V Input and 16V Output voltage, how much current the Input source need to supply.
==> 25uA + 550uA*16V/3V = 25uA + 2933uA = 2958 uA?
Is this right? Seems quite high but i am not sure.
Thanks BR
Hi Maximilian,
Thank you for posting to the MPS Forums. That Quiescent current is indeed incorrect.
Per page 6 of the datasheet, the Quiescent current will be higher on the output pin when the input is set to 3V and the output is set to 16V, and it will remain around 485uA at the VOUT pin given those voltages. The VIN pin will have a typical quiescent current of approximately 25uA.
The total Quiescent current should be approximately 500-525uA given your specifications.
I hope this helps.
Best regards,
Lyell
Thanks for feedback.
But what does a 485uA Output current results in for the input source?
A current at 16V and 485uA on Output result in 7,76mW; Transferred to the Input side end up in 7,76mW / 3V = 2,6mA. Is this a right thinking or do i miss something?
For my application the load of the Input Source is critical due to the fact it is a Battery cell.
Hi Maximilian,
In terms of output power and input power, the values are not equal when dealing with the quiescent current here, because both currents are flowing into the part. The datasheet here can be little difficult to understand with how it is worded when explaining these values, but on the electrical characteristics table it states “no switching” for the quiescent current. However, the part is enabled in that table (unless otherwise stated) so there must be some kind of switching (Or else you would not be able to boost the input). It is to my knowledge that those stated values are recorded while the part is in some kind of “standby” (for lack of a better word) in between switching periods.
The quiescent current on the output is most likely pulling from the output caps that were being charged when the FETs were on, and the input is pulling current from the input caps or the voltage source (In this case, your battery). The sum of both of these currents is the 500-525uA stated earlier.
The reason the input quiescent current is so much lower than the output is because the output is being used to supply VDD since the input voltage is not high enough to supply it.
If you’re worried about the leakage current draining your battery when the part is completely off (Ven = 0), that value is shown under “shutdown current” on the electrical characteristics table on page 4 of the datasheet. That value is 2uA and is measured at VIN, and there will be no leakage at VOUT because the part is not enabled and there is nowhere for it to pull current from on the output side.
Overall, the leakage current should not exceed 550uA when the part is on, and it should not be greater than 2uA when the part is off.