What might this term (N sub C) be, calculating ripple current for a buck converter output capacitor?
I'm reading through the datasheet for TI's TPS54302 step-down converter, and determining values for support components.
There is a calculation to determine ripple current for the output capacitor which is:
$$
I_{COUT(RMS)} = frac{1}{sqrt12} times left(
frac{V_{OUT}times(V_{IN(MAX)}-V_{OUT})}
{V_{IN(MAX)} times L_{OUT} times f_{SW} times N_C} right)
$$
(Where $L_{OUT}$ is the inductor value (H), $f_{SW}$ is the switching frequency (Hz).)
I'm not sure what the term $N_C$ is meant to be.
Looking around online, other formulas omit this. For example, in this document by Rohm titled Capacitor Calculation for Buck Converter IC, page 4 has the formula:
$$
I_{CO} = frac{1}{sqrt12} times left(
frac{V_{OUT}(V_{IN(MAX)}-V_{OUT})}
{L times f_{SW} times V_{IN(MAX)}} right)
$$
Either I am ignorant of what $N_C$ is in this context (the datasheet doesn't clarify); the term is optional depending on application; or TI has a mistake in the datasheet.
What is $N_C$ in this case?
capacitor buck ripple-current
asked 5 hours ago
JYeltonJYelton
15.9k2889190
add a comment |
I'm reading through the datasheet for TI's TPS54302 step-down converter, and determining values for support components.
There is a calculation to determine ripple current for the output capacitor which is:
$$
I_{COUT(RMS)} = frac{1}{sqrt12} times left(
frac{V_{OUT}times(V_{IN(MAX)}-V_{OUT})}
{V_{IN(MAX)} times L_{OUT} times f_{SW} times N_C} right)
$$
(Where $L_{OUT}$ is the inductor value (H), $f_{SW}$ is the switching frequency (Hz).)
I'm not sure what the term $N_C$ is meant to be.
Looking around online, other formulas omit this. For example, in this document by Rohm titled Capacitor Calculation for Buck Converter IC, page 4 has the formula:
$$
I_{CO} = frac{1}{sqrt12} times left(
frac{V_{OUT}(V_{IN(MAX)}-V_{OUT})}
{L times f_{SW} times V_{IN(MAX)}} right)
$$
Either I am ignorant of what $N_C$ is in this context (the datasheet doesn't clarify); the term is optional depending on application; or TI has a mistake in the datasheet.
What is $N_C$ in this case?
capacitor buck ripple-current
asked 5 hours ago
JYeltonJYelton
15.9k2889190
"For this application, Equation 15 yields 296 mA for each capacitor." doh
– Sunnyskyguy EE75
4 hours ago
@SunnyskyguyEE75 It seems plainly obvious now after ThePhoton's answer!
– JYelton
3 hours ago
It is more obvious from the last sentence in spec before the formula. (5) "each capacitor"
– Sunnyskyguy EE75
3 hours ago
@SunnyskyguyEE75 Yeah, I didn't pick up on that. I kept looking for 'N' to be defined somewhere. Sometimes you just have to stop and ask for directions!
– JYelton
3 hours ago
I know. Have a good trip. ;)
– Sunnyskyguy EE75
3 hours ago
add a comment |
I'm reading through the datasheet for TI's TPS54302 step-down converter, and determining values for support components.
There is a calculation to determine ripple current for the output capacitor which is:
$$
I_{COUT(RMS)} = frac{1}{sqrt12} times left(
frac{V_{OUT}times(V_{IN(MAX)}-V_{OUT})}
{V_{IN(MAX)} times L_{OUT} times f_{SW} times N_C} right)
$$
(Where $L_{OUT}$ is the inductor value (H), $f_{SW}$ is the switching frequency (Hz).)
I'm not sure what the term $N_C$ is meant to be.
Looking around online, other formulas omit this. For example, in this document by Rohm titled Capacitor Calculation for Buck Converter IC, page 4 has the formula:
$$
I_{CO} = frac{1}{sqrt12} times left(
frac{V_{OUT}(V_{IN(MAX)}-V_{OUT})}
{L times f_{SW} times V_{IN(MAX)}} right)
$$
Either I am ignorant of what $N_C$ is in this context (the datasheet doesn't clarify); the term is optional depending on application; or TI has a mistake in the datasheet.
What is $N_C$ in this case?
capacitor buck ripple-current
asked 5 hours ago
JYeltonJYelton
15.9k2889190
I'm reading through the datasheet for TI's TPS54302 step-down converter, and determining values for support components.
There is a calculation to determine ripple current for the output capacitor which is:
$$
I_{COUT(RMS)} = frac{1}{sqrt12} times left(
frac{V_{OUT}times(V_{IN(MAX)}-V_{OUT})}
{V_{IN(MAX)} times L_{OUT} times f_{SW} times N_C} right)
$$
(Where $L_{OUT}$ is the inductor value (H), $f_{SW}$ is the switching frequency (Hz).)
I'm not sure what the term $N_C$ is meant to be.
Looking around online, other formulas omit this. For example, in this document by Rohm titled Capacitor Calculation for Buck Converter IC, page 4 has the formula:
$$
I_{CO} = frac{1}{sqrt12} times left(
frac{V_{OUT}(V_{IN(MAX)}-V_{OUT})}
{L times f_{SW} times V_{IN(MAX)}} right)
$$
Either I am ignorant of what $N_C$ is in this context (the datasheet doesn't clarify); the term is optional depending on application; or TI has a mistake in the datasheet.
What is $N_C$ in this case?
capacitor buck ripple-current
capacitor buck ripple-current
asked 5 hours ago
JYeltonJYelton
15.9k2889190
asked 5 hours ago
JYeltonJYelton
15.9k2889190
asked 5 hours ago
JYeltonJYelton
15.9k2889190
asked 5 hours ago
JYeltonJYelton
15.9k2889190
asked 5 hours ago
JYeltonJYelton
15.9k2889190
15.9k2889190
"For this application, Equation 15 yields 296 mA for each capacitor." doh
– Sunnyskyguy EE75
4 hours ago
@SunnyskyguyEE75 It seems plainly obvious now after ThePhoton's answer!
– JYelton
3 hours ago
It is more obvious from the last sentence in spec before the formula. (5) "each capacitor"
– Sunnyskyguy EE75
3 hours ago
@SunnyskyguyEE75 Yeah, I didn't pick up on that. I kept looking for 'N' to be defined somewhere. Sometimes you just have to stop and ask for directions!
– JYelton
3 hours ago
I know. Have a good trip. ;)
– Sunnyskyguy EE75
3 hours ago
add a comment |
"For this application, Equation 15 yields 296 mA for each capacitor." doh
– Sunnyskyguy EE75
4 hours ago
@SunnyskyguyEE75 It seems plainly obvious now after ThePhoton's answer!
– JYelton
3 hours ago
It is more obvious from the last sentence in spec before the formula. (5) "each capacitor"
– Sunnyskyguy EE75
3 hours ago
@SunnyskyguyEE75 Yeah, I didn't pick up on that. I kept looking for 'N' to be defined somewhere. Sometimes you just have to stop and ask for directions!
– JYelton
3 hours ago
I know. Have a good trip. ;)
– Sunnyskyguy EE75
3 hours ago
"For this application, Equation 15 yields 296 mA for each capacitor." doh
– Sunnyskyguy EE75
4 hours ago
"For this application, Equation 15 yields 296 mA for each capacitor." doh
– Sunnyskyguy EE75
4 hours ago
@SunnyskyguyEE75 It seems plainly obvious now after ThePhoton's answer!
– JYelton
3 hours ago
@SunnyskyguyEE75 It seems plainly obvious now after ThePhoton's answer!
– JYelton
3 hours ago
It is more obvious from the last sentence in spec before the formula. (5) "each capacitor"
– Sunnyskyguy EE75
3 hours ago
It is more obvious from the last sentence in spec before the formula. (5) "each capacitor"
– Sunnyskyguy EE75
3 hours ago
@SunnyskyguyEE75 Yeah, I didn't pick up on that. I kept looking for 'N' to be defined somewhere. Sometimes you just have to stop and ask for directions!
– JYelton
3 hours ago
@SunnyskyguyEE75 Yeah, I didn't pick up on that. I kept looking for 'N' to be defined somewhere. Sometimes you just have to stop and ask for directions!
– JYelton
3 hours ago
I know. Have a good trip. ;)
– Sunnyskyguy EE75
3 hours ago
I know. Have a good trip. ;)
– Sunnyskyguy EE75
3 hours ago
add a comment |
1 Answer
1
active
oldest
votes
Most likely, number of capacitors.
If you make your (for example) 100 uF output capacitance using three 33-uF capacitors in parallel, then the ripple current each one needs to handle is only 1/3 of the total ripple current.
(Even though it doesn't look like the parameter is ever explained, nor is the possibility of multiple parallel capacitors discussed, the text immediately above the equation talks about the current for "each capacitor", implying that in some draft the author had the idea of using multiple capacitors, even if this didn't make it into the final version of the datasheet)
answered 4 hours ago
The PhotonThe Photon
83.5k396194
The data sheet doesn't say that $N_C$ is the number of output capacitors, but the schematic has two, and the text says that equation 15 gives the equation "for each capacitor". Bad technical writing style, there TI, to not name all your variables!
– TimWescott
3 hours ago
add a comment |
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1 Answer
1
active
oldest
votes
1 Answer
1
active
oldest
votes
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oldest
votes
active
oldest
votes
Most likely, number of capacitors.
If you make your (for example) 100 uF output capacitance using three 33-uF capacitors in parallel, then the ripple current each one needs to handle is only 1/3 of the total ripple current.
(Even though it doesn't look like the parameter is ever explained, nor is the possibility of multiple parallel capacitors discussed, the text immediately above the equation talks about the current for "each capacitor", implying that in some draft the author had the idea of using multiple capacitors, even if this didn't make it into the final version of the datasheet)
answered 4 hours ago
The PhotonThe Photon
83.5k396194
The data sheet doesn't say that $N_C$ is the number of output capacitors, but the schematic has two, and the text says that equation 15 gives the equation "for each capacitor". Bad technical writing style, there TI, to not name all your variables!
– TimWescott
3 hours ago
add a comment |
Most likely, number of capacitors.
If you make your (for example) 100 uF output capacitance using three 33-uF capacitors in parallel, then the ripple current each one needs to handle is only 1/3 of the total ripple current.
(Even though it doesn't look like the parameter is ever explained, nor is the possibility of multiple parallel capacitors discussed, the text immediately above the equation talks about the current for "each capacitor", implying that in some draft the author had the idea of using multiple capacitors, even if this didn't make it into the final version of the datasheet)
answered 4 hours ago
The PhotonThe Photon
83.5k396194
The data sheet doesn't say that $N_C$ is the number of output capacitors, but the schematic has two, and the text says that equation 15 gives the equation "for each capacitor". Bad technical writing style, there TI, to not name all your variables!
– TimWescott
3 hours ago
add a comment |
Most likely, number of capacitors.
If you make your (for example) 100 uF output capacitance using three 33-uF capacitors in parallel, then the ripple current each one needs to handle is only 1/3 of the total ripple current.
(Even though it doesn't look like the parameter is ever explained, nor is the possibility of multiple parallel capacitors discussed, the text immediately above the equation talks about the current for "each capacitor", implying that in some draft the author had the idea of using multiple capacitors, even if this didn't make it into the final version of the datasheet)
answered 4 hours ago
The PhotonThe Photon
83.5k396194
Most likely, number of capacitors.
If you make your (for example) 100 uF output capacitance using three 33-uF capacitors in parallel, then the ripple current each one needs to handle is only 1/3 of the total ripple current.
(Even though it doesn't look like the parameter is ever explained, nor is the possibility of multiple parallel capacitors discussed, the text immediately above the equation talks about the current for "each capacitor", implying that in some draft the author had the idea of using multiple capacitors, even if this didn't make it into the final version of the datasheet)
answered 4 hours ago
The PhotonThe Photon
83.5k396194
answered 4 hours ago
The PhotonThe Photon
83.5k396194
answered 4 hours ago
The PhotonThe Photon
83.5k396194
answered 4 hours ago
The PhotonThe Photon
83.5k396194
83.5k396194
The data sheet doesn't say that $N_C$ is the number of output capacitors, but the schematic has two, and the text says that equation 15 gives the equation "for each capacitor". Bad technical writing style, there TI, to not name all your variables!
– TimWescott
3 hours ago
add a comment |
The data sheet doesn't say that $N_C$ is the number of output capacitors, but the schematic has two, and the text says that equation 15 gives the equation "for each capacitor". Bad technical writing style, there TI, to not name all your variables!
– TimWescott
3 hours ago
The data sheet doesn't say that $N_C$ is the number of output capacitors, but the schematic has two, and the text says that equation 15 gives the equation "for each capacitor". Bad technical writing style, there TI, to not name all your variables!
– TimWescott
3 hours ago
The data sheet doesn't say that $N_C$ is the number of output capacitors, but the schematic has two, and the text says that equation 15 gives the equation "for each capacitor". Bad technical writing style, there TI, to not name all your variables!
– TimWescott
3 hours ago
add a comment |
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"For this application, Equation 15 yields 296 mA for each capacitor." doh
– Sunnyskyguy EE75
4 hours ago
@SunnyskyguyEE75 It seems plainly obvious now after ThePhoton's answer!
– JYelton
3 hours ago
It is more obvious from the last sentence in spec before the formula. (5) "each capacitor"
– Sunnyskyguy EE75
3 hours ago
@SunnyskyguyEE75 Yeah, I didn't pick up on that. I kept looking for 'N' to be defined somewhere. Sometimes you just have to stop and ask for directions!
– JYelton
3 hours ago
I know. Have a good trip. ;)
– Sunnyskyguy EE75
3 hours ago