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LT8705A, LTC4000 operation error

Category: Hardware
Product Number: LT8705A, LTC4000


For our project, the LT8705A#AEFE and LTC4000#EGN were chosen to output the fuel cell and battery in parallel via diodes.

The conditions we designed are:

Input: 36V, Output: 48V, 5A
Battery charging voltage: 46.2V
Battery charging current: 1.0-2.0A (variable)
Battery Cell: 11CELL

If we test as designed, lt8705a generates heat and normal voltage is not output from INTVcc and LDO33 pins.

Therefore, if the LTC4000 is removed and the current is measured by operating at 36V, 500mA is output and still heat is generated.

We do not know if the FET (Q1) is faulty, but the output voltage seems to float very low at 3.5V.

We want to solve this problem, but we can't.

We refer to the reference circuit diagram and design it according to our specifications. Please let me know if there are any problems or other problems with the schematic we designed during this process.

thank you.


  • If the LT8705A internal LDO has to get its power from a high voltage, the internal LDO will dissipate a lot of power and heat. Try suppling EXTVCC with a voltage of 10V. If the IC is already damaged, you will have to replace the LT8705A first.

  • Thank you for answer.

    I replaced the IC chip because it seemed to be damaged.

    After replacing the IC chip, I took a measurement and it still generates a lot of heat.

    When the diode resistance value (R11) of the GATE power terminal is changed from 4 ohm to 500 ohm, the current is 10 mA and no heat is generated.
    (Current value when resistance value is 4 ohm: 50mA)

    I think I've found the part that causes the heat, but I'm still not sure what's causing it. However, in this case, the SS pin voltage remains at 0.5V.

    Can I get some help on this issue?

  • A current draw of 50mA is easily within the range of normal operation. Internal LDO power dissipation:  (36V - 6V) * 50mA = 1.5W. If you supplied EXTVCC with a 10V supply, power dissipation in the LDO would be:  (10V - 6V) * 50mA = 0.2W. If the LT8705A doesn't have an excellent thermal path to dissipate the heat, it would easily get too hot with 1.5W of dissipation.

  • hello.
    What is the difference between lt8705 and lt8705a?
    Can I use the lt8705a on the demoboard dc2924a circuit?
    thank you.

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