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Low noise regulator for DAC & clock
Low noise regulator for DAC & clock
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Old 25th January 2019, 05:45 PM   #181
Thorp is offline Thorp
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Quote:
Originally Posted by phase View Post
I also though it was odd to suggest such a huge part for something that requires such a tiny amount of power instead of another means to a quiet source. [...]
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Originally Posted by Joseph K View Post
In fact, there is a controversy about that extra cap in the AKM4490 datasheet. The curious fact is that there had been a datasheet update in course, and the new one does not show this part any more!
Do any of You have any more insider insight on it?

AKM is a little more specific in the AK4493 datasheet:
"The differential voltage between VREFHL and VREFLL, and VREFHR and VREFLR set the full-scale of the analog output range. The VREFHL/R pin is normally connected to 5.0V reference voltage, and the VREFLL/R pin is normally connected to the 0V reference voltage. Connect a 0.1F ceramic capacitor and 470F (min. value depends upon power supply quality) electrolytic capacitor between VREFHL and VREFLL, and VREFHR and VREFLR. Especially the ceramic capacitors should be connected as near as possible to the pin. The VREFHL, VREFHR, VREFLL and VREFLR pins should avoid noises from other power supplies. Connect the VREFHL/R pin to the analog 5.0V via a 10Ω resistor, and the VREFLL/R pin to the analog ground via a 10Ω resistor when it is difficult to obtain expected analog characteristics because of noises from other power supplies (A low pass filter of fc=17Hz will be composed with the 470F capacitor and the 10Ω resistor. It removes signal frequency noise from other power supply lines)."
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Old 25th January 2019, 06:02 PM   #182
jan.didden is offline jan.didden  Europe
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Originally Posted by Thorp View Post
You are right too, I thought the graph expresses itself:
I referred to the bandwidth limitation region of the graph only. If Cout is 22uF, you are right - PSRR increases, but the inflection point of the graph is moving to the left and as you can see, if there is a ripple in the input circuit to aprox. 1.8Mhz is better for Cout to be 10uF because in the 22uF situation PSRR is already descending.
I admit it may look strange to someone who cannot read my thoughts.
I admit the talk about 'inflection point' and such is creative. ;-) But it is not really about inflection point or bandwidth of PSRR. It is about the absolute value at each frequency, and with larger C the curve is always the same or above than with lower C. So higher C is better for PSRR.

Jan
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Old 25th January 2019, 06:49 PM   #183
Thorp is offline Thorp
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Originally Posted by jan.didden View Post
I admit the talk about 'inflection point' and such is creative. ;-) But it is not really about inflection point or bandwidth of PSRR. It is about the absolute value at each frequency, and with larger C the curve is always the same or above than with lower C. So higher C is better for PSRR.

Jan
As I already told you, I was referring to the region where the larger C curve is not above to the lower C curve, in the following context:
- the manufacturer says "larger values of output capacitor only marginally improves the performance because the regulator bandwidth decreases with increasing output capacitance"
- the graph in the datasheet only shows 2 close values 10uF and 22uF, but we were talking about 560uF and the difference between its curve and the lower 10uF C curve should be more significant.
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File Type: png LT3045_PSRR_Cout.png (48.2 KB, 117 views)
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Old 25th January 2019, 06:55 PM   #184
Daudio1 is offline Daudio1  United States
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Quote:
Originally Posted by Thorp View Post
I missed that part - about audiophiles, it is about the perception, everybody has it's own datasheet. Good luck.
Right back at you

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Originally Posted by Thorp View Post
"For stability, use a minimum 10F
output capacitor with an ESR below 20mΩ and an ESL
below 2nH. Large load transients require larger output
capacitance to limit peak voltage transients.[...]
Given the high PSRR and low noise performance attained
using a single 10F ceramic output capacitor, larger values
of output capacitor only marginally improves the perfor-
mance because the regulator bandwidth decreases with
increasing output capacitance — hence, there is little to
be gained by using larger than the minimum 10F output
capacitor. Nonetheless, larger values of output capacitance
do decrease peak output deviations during a load transient."
Where did this quote come from ? It seems to match my understanding.
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Old 25th January 2019, 07:03 PM   #185
Thorp is offline Thorp
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Originally Posted by Daudio1 View Post
Where did this quote come from ? It seems to match my understanding.
Page 13 (OUT (Pin 10/Pins 11, 12) and page 16 (Stability and Output Capacitance) from LT3045 datasheet.
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