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UA78M: What is the minimum output load current of UA78M33CDCYR

willson
Prodigy 160 points
Part Number: UA78M
Other Parts Discussed in Thread: LM1117, TLV1117LV

What is the minimum output load current of UA78M33CDCYR，recently  I use UA78M33CDCYR to power supply the MCU at 3.3 V  when  the mcu in the  standby mode .  the  UA78M33CDCYR 's out voltage is 4.0~4.2 V, the  current of  mcu  at standby  mode is 3-10uA, so i guess the LDO has the minimun requriemet of   output load current. mybe 100uA,1mA? or more. if the LDO run in No output load,its out voltage will not be fixd and go up.Is that right?

  • 0
    TI__Mastermind 23361 points

    Hi Wilson,

    UA78M needs a typical 4mA - 5mA current to ensure the bias circuit at the input has a good reference voltage. Therefore, the minimum load used in the Electrical Characteristics table is 5 mA. As such, the minimum load to achieve the Electrical Characteristics specifications is 5 mA.

    Regards,
    Jason Song

  • 0 in reply to Jason Song
    Prodigy 160 points

    Hi  jason:

    thank you for you reply , if so the  UA78M 's can't meet my mcu standby mode working in 10 uA  current.  I have three questions to ask you.  hope you can help me to answer it.

    1，Does  every LDO has minmun load current  for voltage requlation. as i known if the LDO need it ,it's datasheet will directly give the characteristics. such as LM1117,s minmun load current is 1.7mA.

         but the minmun load current in Electrical characteritics is 10mA.

    2 , Does the LDO have very Low load current for voltage requlation about 10uA current?  i checked most of LDO ,s minmun load current is 1mA  to achieve the electrical characteristics specifications. and some 

    LDO of ADI  minmun load current is 100uA .

    3 , if  not such LDO, Can i use  additional ceresistance or Voltage regulator diode in LDO output load to achieve the electrical characteristics specifications, Or have better suggestions.

    thank your!

  • 0 in reply to willson
    TI__Mastermind 23361 points

    Hi Wilson,

    1，Does every LDO has minmun load current for voltage requlation. as i known if the LDO need it ,it's datasheet will directly give the characteristics. such as LM1117,s minmun load current is 1.7mA. but the minmun load current in Electrical characteritics is 10mA.

    --Newer design normally require small or no load current for the LDO to stay in regulation; the minimum load is usually satisified with the resistor devider. For LM1117, you are correct. The minimum load required is 1.7mA but the electrical characteristics table are using 10mA.

    2 , Does the LDO have very Low load current for voltage requlation about 10uA current? i checked most of LDO ,s minmun load current is 1mA to achieve the electrical characteristics specifications. and some LDO of ADI minmun load current is 100uA .
    --If you can provide more details on your appliation, we can try to recommend you the ones to meet your requirement.

    3 , if not such LDO, Can i use additional ceresistance or Voltage regulator diode in LDO output load to achieve the electrical characteristics specifications, Or have better suggestions.
    --For UA78M, the biasing circuit needs to have 4.8mA for the LDO to regulate. As long as enough biasing currrent has been provided, it does not matter what kind of load you have. Again, if you are flexible on picking other pacakges and providing the details of your application, we may be able to recommend you another LDO that requires much less minimum load.

    Regards,
    Jason Song

  • 0 in reply to Jason Song
    Prodigy 160 points

    Hi Jason :

         I want to choose an LDO to power the  STM32F105  .  Input voltage is 5V and  ouput voltage need 3.3V   maximum current is 250mA   package name  need SOT-89 or SOT-223. package  pin are Vin and  Vout  and GND   Please pay attention  the  STM32F105    it's current consumptions in Stop and Standby modes are 38uA  and 3.8uA.  hope you to recommend an LDO to meet  above requirements.

  • 0 in reply to willson
    TI__Mastermind 23361 points

    Hi Wilson,

    You may consider TLV1117LV, It is in SOT-233 and needs no bias current. At no load, the device only requires about 50uA to operate.

    Regards,
    Jason Song