Using LT3045-1 with Vin=15V, Vout=5V, Iout=30mA

Question

Hi, 
 
 I want to use LT3045-1 to generate an ultra-low noise 5V output voltage from a relatively noisy 15V input voltage. 
 Since the output current I need is just 30mA, 10V input-to-output-differential voltage should not be an issue I think. 
 
 However, in order to be on the safer side, I am considering using two LT3045-1 for my application. 
 I had two ideas in mind:

1) Connect two LT3045-1 in series and do the voltage conversion in two steps. First convert 15V to 10V. Then convert 10V to 5V. 
 
 2) Connect two LT3045 in parallel where both of them have 15V input and 5V output. 
 
 Which of the options above would be better in terms of power dissipation and output noise do you think? 
 
 Thank you very much for your time and suggestions. 
 
 Best regards.

Alexxx · Accepted Answer

Hi bahadirdonmez , 
 paralleling could give you a slightly (0,707) lower noise than serial connection, but there is the problem of good current sharing, so you need an output resistor, that can diminish regulation quality. How about another proposal (if your load current does not have high current spikes) - use just one regulator - put in front of your regulator following: 1.) R-C low pass filter. Make R 220 Ohms, 1/4 W and C at least 10&micro;F. The voltage drop of the resistor will lower regulators input voltage, dissipate the heat AND you get an additional low-pass filter of Fg= 72Hz. You can place the R-C "far away" from regulator. Keep in mind, that you must avoid that your noisy environment at high frequency couples into the ground plane. For lowest output noise you have to use a big capacitor at the SET-pin.)

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Using LT3045-1 with Vin=15V, Vout=5V, Iout=30mA