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regarding one voltage regulator

actually i am converting 12V TO 5V USING ONE REGULATOR LTM4601.

I HAVE DESIGNED CIRCUIT AS PER HIS REFERENCE CIRCUITRY DESIGN.

IN THAT HE USED FEEDBACK RESISTOR (RFB) AS 8.25KOHMS TO CONVERT 12V TO 5V. BUT IN OUTPUT I AM NOT GETTING 5V,IT IS SHOWING ALMOST 7.65V.

this is the formula i have used for convert voltage

              VOUT = 0.6V • 60.4k +RSET RSET

Table 1. RSET Standard 1% Resistor Values vs

VOUT RSET (kΩ)            Open          60.4           40.2         30.1       25.5      19.1            13.3             8.25

VOUT (V)                          0.6              1.2             1.5             1.8        2           2.5              3.3                5

then i did small modification in design BOM, i have changed RFB value from 8.25k to13k. 

finally i got  5V but still i am in confusion state that i have designed according datasheet only **** output is varied as i said previous.

  • Hi bshivakumar, 

    The datasheet has a 12V to 5V application circuit shown in Figure 16. Is this the datasheet figure being referred to for your schematic setup?

    Note for Vout higher than 3.3V (ie 5V output) please ensure that the remote sense amplifier is not used (ie connect VOSNS+ to GND, connect VOSNS- to INTVCC, float DIFF_OUT) and that local output voltage sensing is set up properly (ie connect VOUT_LCL to Vout, connect 8.25k from VFB to GND). The remote sense amplifier would not have enough headroom to operate properly if trying to sense outputs greater than 3.3V, in which case can result in the output going above the expected programmed output voltage. 

    Can you confirm your setup has disabled the remote sense amplifier and set up local sensing properly? You may also contact me at Samuel.Young@analog.com if you would like me to double check your actual application circuit. 

    Thanks. 

  • The Vout formula should be:

    Vout=0.6V x (60.4K+Rset)/Rset.

    The data sheet formula is correct. Please check other things, such as differential remote sensing connection. Thanks.

  • THANKS BUT WHAT IS THE REASON FOR VARIATION IN VOUT.(ie, >3.3 ) y it is

    giving like that.

    --

    Thanks and regards,

    --

    B.Shivakumar

    Application engineer

    Unistring Tech Solutions Pvt Ltd

    www.unistring.com

    7396110499/9676996484

    On Thu, Jun 28, 2018 at 10:56 PM SYoung <

  • Hi B. Skivakumar, 

     

    Can you confirm in your setup where you saw issue that your remote sense amplifier is enabled? If you would like me to double check your schematic please send to Samuel.Young@analog.com

    If your remote sense amplifier is enabled the issue is the remote sense amplifier is being used for 5Vout which is too high for it to support (users should disable this for Vout > 3.3V as mentioned in the datasheet). The remote sense amplifier requires enough headroom (between sensed output voltage and its bias supply) to function properly. For 5Vout case it will not be able to output a properly high enough voltage back to VOUT_LCL pin, in which case the LTM4601 will think the output voltage is lower than it actually is and so increase the duty cycle to increase the output voltage, resulting in an output voltage above that programmed by the resistor from VFB to GND.

    Thanks. 

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