LTC3350

Hello,

I'm using the LTC3350 in a product. The product regulates power to different hardware, basically a I/O module for hardware. One output needs a UPS for data security purpose.

I don't understand the difference of the LTC3350 and LTC3351 completely. I know the LTC3351 is 'hot swappable', but what does this exactly mean? Does it mean you can disconnect the output load and connect again when the LTC3351 is in backup mode? Or does it mean you can disconnect and connect the input of the LTC3351? Because the latter you can do too with the LTC3350 as I understand from the datasheet..

My unit needs to be able to provide power to the load for about 15 seconds when power input is suddently disconnected, Load is drawning 1,5 A average @ 12 V. Is this possible with the LTC3350? And can you tell me the exact difference with the LTC3351?

The circuit of the UPS unit of the circuit is below.

Parents
  • 0
    •  Analog Employees 
    on Aug 16, 2019 5:25 PM over 1 year ago

    Hello, The main difference is the hotswap front end. If this circuit is to be removed and plugged into a system while operating like a swappable disk drive, then the hot swap from end will allow the user to safely do that. It is not to hot swap the load.

    the charger boost circuit is exactly the same. There are some more added features with the LTC3351 for telemetry control.

    the backup calculator that helps size the capacitor stack and current limit for the LTC3350 can also be used for the LTC3351. See the link below.

    https://www.analog.com/media/en/simulation-models/software-and-simulation/LT3350BackupCalculator_R1.xlsx

  • Hello MartyM,

    Thank you for your reply. The calculation sheet is handy. Still I have one question left. I understand the LTC3351 is hot swappable, so you can unplug front end and plug it in again without power interuption for the load.

    But isn't this possible for the LTC3350? Because it is used for UPS. So I assumed that if the input fails for let's say 3 seconds and than kicks in again, the LTC3350 will manage this and the load doesn't notice the interupt.

    Or will the LTC3350 just switch to backup state when the input power fails and stay in backup until the capacitors are fully empty, no matter what the input does? But in the latter, how do you reset?

    Thank you again.

    Rick Meijers

  • 0
    •  Analog Employees 
    on Aug 19, 2019 12:39 PM over 1 year ago in reply to Rick Meijers

    Hi Rick,

    The LTC3350 only has an ideal diode front end. It will quickly disconnect turn off the INFET and prevent any back feeding from the backup controller to the input but cannot control the inrush current or VOUT slew rate if the part is plugged into a hot power bus. A back to back FET is needed to control the inrush current and slew rate to prevent any damage to the INPUT FETs and sense resistor as the system output capacitors are charge up.

    The LTC3351 hot swap controller also has a circuit breaker feature that will disconnect the input when too much current is drawn. The LTC3350 can only reduce the charger to near 0A when the load draws too much power.

    Regards,

    Marty

Reply
  • 0
    •  Analog Employees 
    on Aug 19, 2019 12:39 PM over 1 year ago in reply to Rick Meijers

    Hi Rick,

    The LTC3350 only has an ideal diode front end. It will quickly disconnect turn off the INFET and prevent any back feeding from the backup controller to the input but cannot control the inrush current or VOUT slew rate if the part is plugged into a hot power bus. A back to back FET is needed to control the inrush current and slew rate to prevent any damage to the INPUT FETs and sense resistor as the system output capacitors are charge up.

    The LTC3351 hot swap controller also has a circuit breaker feature that will disconnect the input when too much current is drawn. The LTC3350 can only reduce the charger to near 0A when the load draws too much power.

    Regards,

    Marty

Children
  • Thank you Marty, that's clear.

    Only question left is how does the LTC3350 handle a reset or detect a reset? I can't find anything about it in the datasheet. When can you plug it in again after a power failure? 

    Regards,

    Rick

  • 0
    •  Analog Employees 
    on Aug 23, 2019 12:28 PM over 1 year ago in reply to Rick Meijers

    Hi Rick,

    The LTC3350 has a graceful power down. The switcher stops first as INTVCC drops below UVLO falling threshold around 4V. As VOUT continuous to fall the last thing that occurs is the digital registers lose power when the VCC2P5 register drops out. This is not speced but I think is typically below 2V. When the Power returns and the VCC2P5 is powered up then everything is reset to the default values. If power fails and the VOUT voltage is high enough that the VCC2P5 register does not lose power then the logic will not be reset and the digital registers will keep their contents.

    Regards,

    Marty