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TINA/Spice/TPS61086: TPS61086

Part Number: TPS61086
Other Parts Discussed in Thread: TINA-TI, , LM555

Tool/software: TINA-TI or Spice Models

Hi,

I am trying to use the TPS61086 configured as a charge pump doubler. The boost converter is deisgned to boost voltage from 3.3V to 7V (Vout_boost net in the schematic attached). This voltage is then doubled and stored in a bank of three 820uF capacitors. (2Vout_boost net in the schematic attached). The working is as follows

When switch node SW = 0V i.e., the device is ON, the flying capacitor C3 is charged to Vout_boost – SD3 

When device is off, i.e., the switch is open then SW = Vout_boost + SD1.

 Now voltage on C10, C11, C12 becomes Vout_boost + SD1 + Vout_boost –SD3 = 2Vout_boost + SD1– SD3 and ignoring the diode voltage drops , this voltage of 2Vout_boost is transferred to the output capacitors C10, C11,C12

I am trying to simulate the output waveforms using TINA. The output waveform for Vout_boost net is correct - at approximately 7.2V but the waveform for the 2Vout_boost net  shows as 7V. 

What is wrong with the way I am trying to simulate and how can I get it work? I should be able to see Vout_boost as 7V and Vout_boost as aprroximately 12V considering diode voltage drops.

  • Hello,

    Please follow the guidelines in the following post and share your TSC file.
    Also, is this based on an actual TI recommended application? I am trying to understand if this is something that has been tested on the bench before and verified.

    e2e.ti.com/.../592360
  • Hi Nikhil,

    Yes, the design is based on an application note - www.ti.com/.../slva398a.pdf

    We have not tested this on bench. We actually wanted to try simulating this on TINA first before we design a PCB for testing because that will save us some cost and time.
  • Thanks. Can you share your TSC file as well? We like to start from your exact file rather than having to recreate it from scratch (which can lead to mismatches in what we are debugging).
  • Hi Nikhil,
    the schematic is attached in the post above.
    Thanks
  • Can the flying capacitor C3 be modelled as a voltage source?

  • Hi,


    The flying capacitor should be typically between 100nF to 1uF.

    The storage capacitors are too high for a frequency of 1.2MHz.

    I have modified the capacitors and its working now. PFA the same.

    Thanks,

    Durga

  • Hi, 

    Thanks for the corrected schematic. It seems to work fine now.

    I really appreciate the quick response. :)

    Regards

    Preethi

  • Hi,

    Just another quick question -

    The reason I put three 820uF capacitors for the storage caps in my schematic is because I wanted them to provide 100mA for 200ms which is like 0.02 couloumbs of charge. The caps will be charged to only about 10V considering the drops across the diodes and the ESR losses and can only be discharged down to 3.2V so this will be (10V-3.2V) = 6.8V. Since Q = C * V  => 0.02 Coulombs of charge = C * 6.8V so C = 2.9 mF so putting three 820uF caps in parallel (2.46mF) which is somewhat close to 2.9mF.

    Is there any way that the schematic can be modified to achieve this?

     The circuit does not work with high value of storage caps as you rightly pointed out. What is the maximum value that I can use? 

  • Hi,


    The selection of capacitor on a system depends on frequency with which it is running, ripple that is needed and the load we need to drive.

    Please refer on selection of the load capacitor.

    How ever you can still use the same schematic that was shared to use for 100mA load. PFA the schematic for your reference and the results(ripple is very low in this case).

    8267.TPS61086 Vout7V_REV1.TSC

  • Hi,

    I have a small problem with the circuit that I have attached. The circuit is basically is an extension of the TPS61086 configured to boost 2.3V to 4.5V to 8V with a charge pump doubler circuit. 

    Vout_boost is  8V as expected and the voltage levels at VF1 and 2Vout_boost is 12.45V. 

    There is a timer circuit configured in the astable multivibrator mode with an on time of 250ms and off time of 180ms that enables or disables the TPS61086.

    I would like to replace the timer circuit with a comparator based solution that monitors the capacitor voltage - 2Vout_boost and if this voltage is less than or equal to 3.3V the enable of the TPS61086 should be high and it should be high until the 2Vout_boost voltage reaches 12V after which it should be low.

    I am thinking of using hysteresis based comparators but the caveat is that I want the Vcc of the comparator to be between 2.3V to 4.5V and the voltage that I will be monitoring is between 3.3V and 12V . The voltage range at the inputs of the comparators are normally only up to (Vcc + 1V) maximum. Is there any work around for this problem?

  • Hi,

    Use Lm555 is also a very good option. You can determine the on time by the boost converter's startup waveform, determine the offtime by the boost converter's output voltage falling waveform.
    If you want to use a comparator, then you have to divide the output voltage to a Value <Vcc. something like the attached circuit.

  • Hi, 

    Thanks very much for your continued support. I tested my circuit practically and found that the peak current drawn from the supply shoots upto about 3A when it switches on. Such very high values for peak currents are not very good especially for a battery powered product such as ours. I tried to extend the soft start time by adding a diode and capacitor combination as was mentioned in application note slva553 and it is highlighted in red in my circuit below but the current drawn from the supply as shown by AM2 is still about 530mA. Is there anyway to reduce this high inrush current? (The expected value at Vout_boost is 8V and at 2Vout_boost is 13V. The enable of the regulator is controlled by a hysteresis comparator which I haven't shown here right now. The EN is switched off when the 3x820uF caps charge upto 12.7V and it is switched on when it is discharged to 3.3V.)

    Thanks very much

    Regards

    Preethi

  • Hi,

    530mA is already very small in this application. If you want to further reduce the inrush current, then you need to further reduce the output capacitance. acturally, when Vo<3.3V, the input current is uncontrolled, reduce output cap is the only method.

  • Hi,

    I am trying to step down the voltage at the output of the charge pump ( which is 12V) using a buck converter that will regulate it to 3.3V but the voltage at the buck output is 3.65V instead of 3.3V which is not desirable for the load. In another forum, I read that it would be easy to just regulate the charge pump voltage using a linear regulator. Is there any reason why the charge pump wouldn't work well with a buck regulator?

    Thanks

    Preethi

  • I think the buck converter is disturbed. maybe the reference voltage is changed.

  • The input voltage is 3.3V, why you use charge pump circuit to generate the 3.3V output?
  • So, the idea is this - we want to use 4xAA alkaline cells which gives 4.5V -> boost it upto 12V using a charge pump -> detect if the 3x820uF caps have charged upto 12V and then disable/shutdown the boost converter so that the battery is cut off and no current is drawn from it. The voltage on the charge pump caps (12V) will be regulated to 3.3V by a buck converter already on the board of one of our products. We monitor when the 3x820uF discharge to 3.3V and then enable the boost converter again. The lower threshold is set at 3.3V because the buck converter can work from 3.2V to 15V. The schematic shows 3.3V input from battery because that is the average battery voltage. The alkaline batteries have a gradual decrease in their voltage, so I simulated with their average voltage. We want to see if this will improve battery life.

    Thanks
    Regards
    Preethi
  • Thanks for the update, why use charge pump output generate 3.3V, not use main 12V generate 3.3V, which is much stable!