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TPS61222 when input voltage is 5.5v

Daniel Dan
Prodigy 50 points
Other Parts Discussed in Thread: TPS61222, TPS63050

Hi,

My application need a DCDC which input voltage range is 4.0v to 5.5v, input current max is 120mA, output voltage is 5.0v, load current max is 100mA and operation temperature is -20C to 100C.

I test the TPS61222 using Typical Application Circuit in datasheet. But when input voltage is bigger than 5V(like 5.1v to 5.5v),  the output voltage has a bigger/worse ripple. 

How to get a good performance output with 4.0 to 5.5v input?

Thanks.

Daniel

  • 0
    TI__Mastermind 46905 points
    Daniel
    the behavior is normal for TPS61222 at VIN> VOUT condition, there is not good solution. maybe you can try to parallel a Schottky diode between SW and VOUT pin, the ripple should be smaller. if you require regulated 5V output voltage at 4.0~5.5V range, you should select a buck-boost converter, TPS63xxx series.
  • 0 in reply to Jasper Li
    Prodigy 50 points

    Hi, Jasper,

    Thanks for your reply.

    I find the operation temperature of TPS63xxx is -40C to 85C, but my application is -20C to 100C.

    You mentioned "parallel a Schottky diode between SW and VOUT pin", may I know what's "SW" meaning?

    Regards,

    Daniel

  • 0 in reply to Daniel Dan
    TI__Mastermind 46905 points
    it is "L" pin. this pin is switching during operation. so we also call it SW pin.
  • 0 in reply to Jasper Li
    Prodigy 50 points

    Thanks, Jasper.

    Does the circuit like below?

  • 0 in reply to Daniel Dan
    TI__Mastermind 46905 points
    yes. you are right. i also check this in the EVM. the ripple could reduce to worst 250mV level (change with the VIN and load current ). the schottky diode help, but ripple is still high :(

    what the 5V is used to power in you project?
  • 0 in reply to Jasper Li
    Prodigy 50 points

    Hi, Jasper,

    My project is a industrial sensor, and sensor output sin/cos analog signals.

    Normally, the typ.5V (5.5v~4.5V) input power comes from external driver. (input voltage will supply my ICs which work at 5.5v~4.5V)

    But, the worst case, due to the attenuation of long cable, the input voltage is 4V to my sensor. (the ICs couldn't work.)

    I want to add a DCDC, to increase the input voltage to 5V when input is below 4.5V when input range is 5.5V~4V.

    If ripple is bigger, the performance of my sin/cos analog signals is worse. 

    Do you have any suggestions? (BTW, my sensor operation temperature is -40C~100C,  but most DCDC is max. 85C)

    Regards,

    Daniel

  • 0 in reply to Daniel Dan
    TI__Mastermind 46905 points
    the performance of the sin/cos analog signal is also relates to the Power Supply Rejection Ratio (PSRR) and the Signal Noise Ratio (SNR)of the sensor. You can add an LDO between the boost converter and the sensor.

    most power devices can operates at 100C, if you can keep the junction temperature not higher than 125C. this would relate to the power loss of the device and its PCB layout.
  • 0 in reply to Jasper Li
    Prodigy 50 points

    Thanks, Jasper.

    Will you please recommend the part number of DCDC+LDO which input 4.0~5.5v/150mA(max.), output 5v/100mA(max.) and operation temperature Max.100Ca

  • 0 in reply to Daniel Dan
    TI__Guru*** 145710 points
    The TPS63050 is a good buck-boost to use. It has a forced PWM mode for lowest noise.

    We recommend that it be used below 85 C ambient, but at your low power the junction should easily be below the 125 C limit.