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Application of LTM8064

Datasheets on LTM8064 show a circuit of 2 supercapacitors. Can I apply this circuit to 16 supercapacitors? What is
the advantage of this circuit over a transistor in key mode and shunting resistor balance circuit?

  • How many supercaps you can series for the example configuration will depends on the output voltage and current requirements, etc. In theory, it may be fine for more than two (or even 16?) stacked. Make sure any time, especially during transients, all LTM8064 pin maximum rating requirements have been met. For example, Vout pin should always be lower than 40V. The voltage across each supercap is regulated by a module separately, therefore, the voltages are well controlled. Thanks.

  • For LTM8064 to charge three SuperCapacitor in series connection, will there be a need for passive balancing with resistor?

    If required, what is the considerations for the balancing resistor?


  • Hello,Chaz!

    A break in my questions due to the time to develop a battery of 16 s/k. As a basis, I took a diagram from Data Sheets on LTM8064 (see "Stack Two LTM8064s to Charge and Active Balance Supercapacitors"). In the diagram: Rfb = 17 .8k (Uout = 2 .3V * 16 = 36 .8V), CTRL1 = VREF, CTRL2 - divider for Imax (Sources) = 3 .4A, Imax (Sinks) = 4 .5A.

    Question: 1) In Table 1 for Cout, two capacitors 470 and 220 μF are indicated, and in the diagram that I took as the basis - only one, equal to 100 μF. What should be guided by a schema or table?

    2) In the scheme, the MODE output is free, which means 2-Quadrant for Actively Balance Supercapacitors. In this case, has the INPUT PROTECTION scheme become mandatory?

    3) Calculation of INPUT PROTECTION scheme. I took the fig scheme as the basis. 6b from Data Sheets on LTM8064.

    The protection activation threshold is 50V. The input protection circuit should be designed to absorb at least 2.3V*4.5A=10.35W. Then the circuit must be designed to be able to dissipate 10.35W and accept 10.35W/50V = 207mA. With the simultaneous operation of 16 LTM, this current increases to 3,312A. To limit the current through MOSFET, switch on the 15 ohm resistor in series with MOSFET.

    Please confirm or criticize my calculation.

    4) Will the suppressor be able to perform the functions of the INPUT PROTECTION circuit?


  • The output cap will depend on what kind of load. Note, supercap is the load in the example.

    Input protection is optional. (It depends on the requirement of the system, previous section...).

    When designing input protection circuit, make sure Vin will never exceed maximum rating (60V). Thanks.

  • Hello, Chaz. O’key.
    There was another question. I limited the battery charge current to 3.4 A (divider by CRL2). When the battery has no load during charging, the current at the input of LTM does not exceed 3.4 A.
    When the battery has a load at the time of charge - the current at the input of LTM exceeds 3.4 A. So we can conclude that LTM somehow, in addition to the charge current, additionally give the current to the load in excess of 3.4 A?