RobustPCBWhere Robust Design Starts
CalculatorsالعربيةUpgradeSign inSign up

What's new

Full changelogEngine 1.26.4

MLCC Effective Capacitance

Power & Regulators

How much of this ceramic capacitor is left at your voltage, temperature and age?

Inputs

The part's marked value.
F
22 µF
From the part's datasheet.
V
From the tolerance code: J 5 %, K 10 %, M 20 %.
%
The highest DC across the part, plus the ripple peak.
V
Read the maker's DC-bias curve or tool for this part number at Vdc (about 0 for C0G). Read it again whenever Vdc changes.
%
Include self-heating from ripple. Also checks the dielectric's rated range.
°C
Your design's minimum.
F
4.7 µF
Ageing and low temperature
The age to check, from the last reflow. Use the product's service life for the worst case.
h
The datasheet's reference time for value and tolerance (KEMET: 48 h or 1 000 h by part).
h
Datasheet, % per decade-hour. Blank: C0G 0, X7R 3, X5R 5, Y5V 7, Z5U 7 (KEMET maxima), X6S and X7S 5 (assumed).
%/decade
The part's operating range.
°C

Results

Total effective capacitance n·Cmin
5.702µF
Pass

Checked: total ≥ your 4.7 µF requirement, failing below 0.9 × (design margin): 1.213 × here, with 4.71 % ageing at 8760 h
Show working
  1. Ageing lossΔA = a × log10(t / t_ref) = 5 % × log10(8760 / 1000) = 4.71 %
  2. Effective capacitance per partC_min = C × (1 − tol) × (1 − b) × (1 − ΔT) × (1 − ΔA) = 22 µF × 0.8 × 0.4 × 0.85 × 0.9529 = 5.702 µF
  3. Parts neededN = ⌈C_req / C_min⌉ = ⌈4.7 µF / 5.702 µF⌉ = 1
  4. Total effective capacitancen × C_min = 1 × 5.702 µF = 5.702 µF, 1.213 of 4.7 µF
Effective capacitance per part Cmin
5.702µF
Parts needed N
1
Voltage ratio Vdc/Vrated
0.794
All results (2)
At nominal value (no tolerance) Cnom,eff
7.128µF
Total loss
74.1%
Each loss, per part
LossOf what is leftCapacitance lostLeft
Tolerance20 %4.4 µF17.6 µF
DC bias60 %10.56 µF7.04 µF
Temperature15 %1.056 µF5.984 µF
Ageing4.71 %282 nF5.702 µF
Totalof nominal: 74.1 %16.3 µF5.702 µF

Accuracy

Source
  • R. Fiore
  • KEMET multilayer ceramic capacitor datasheets: ageing rate (maximum % capacitance loss per decade hour) and referee time

R. Fiore, Dielectric Aging Phenomena, American Technical Ceramics, Circuit Designer's Notebook the equation

KEMET multilayer ceramic capacitor datasheets: ageing rate (maximum % capacitance loss per decade hour) and referee time a published table

Checked against: EIA-198, temperature characteristic codes for ceramic capacitors (X5R, X7R, X6S, X7S, Y5V, Z5U, C0G)

Precision
Exact arithmetic on four worst-case losses, treated as independent and multiplied.

The temperature term is the class code's limit rather than this part's curve, and the DC-bias loss is your own reading of the maker's curve, which usually dominates the answer.

Most of the uncertainty comes from DC-bias loss at Vdc. Tighten that first.

Verified against

1 independent case. See the working.

This is a design aid. The engineer remains responsible for the design and for checking the standard itself.

Parameter sweep

Vary one input over a range and see the answer and verdict at each step, as a table and a curve.Pro

Worst-case corners

Put a tolerance on each input and get the worst-case band around the answer.Pro

Derating

The principle

A ceramic capacitor's marked value is not what the circuit gets. Its tolerance, the DC voltage across it, its temperature and its age each take a share, and on X5R, X7R, Y5V and the like the DC bias can take the most. This page takes each loss at its worst, multiplies them, and says how many parts in parallel meet your requirement. The DC-bias loss is your reading of the maker's curve: the page offers no estimate of it.

Effective capacitance, worst case
Cmin=C (1−tol) (1−b) (1−ΔT) (1−ΔA)C_{min} = C\,(1 - \t{tol})\,(1 - b)\,(1 - \Delta_T)\,(1 - \Delta_A)
The four losses are treated as independent and multiplied, a design choice. Without the tolerance term it gives the value at nominal, Cnom,eff.
Temperature, class II and III (the class limit)
ΔT=class limitfor  Tmin≤T≤Tmax\Delta_T = \t{class limit} \quad \t{for}\; T_{min} \leq T \leq T_{max}
EIA-198, minus side: X5R and X7R 15 %, X6S and X7S 22 %, Y5V 82 %, Z5U 56 %. The page uses the limit, not this part's curve.
Temperature, C0G (30 ppm/°C)
ΔT=30×10−6⋅max⁡(∣Tmin−25∣,  ∣Tmax−25∣)\Delta_T = 30 \times 10^{-6} \cdot \max\left(|T_{min} - 25|,\; |T_{max} - 25|\right)
T in °C. C0G is 0 ± 30 ppm/°C about 25 °C (EIA-198).
Ageing
ΔA=a log⁡10ttref(t>tref),ΔA=0(t≤tref)\Delta_A = a\,\log_{10}\frac{t}{t_{ref}} \quad (t > t_{ref}), \qquad \Delta_A = 0 \quad (t \leq t_{ref})
a in % per decade-hour, from the datasheet. Value and tolerance are indexed to the referee time tref, so there is no ageing credit before it (KEMET).
Parts needed
N=⌈CreqCmin⌉N = \left\lceil \frac{C_{req}}{C_{min}} \right\rceil
n parts in parallel give n·Cmin.
  • CCnominal capacitance of one part
  • tol\t{tol}tolerance, minus side
  • bbDC-bias loss at Vdc, read from the maker's curve
  • ΔT\Delta_Ttemperature loss
  • TTthe part's temperature
  • Tmin, TmaxT_{min},\,T_{max}lowest and highest temperature in use, °C
  • ΔA\Delta_Aageing loss
  • aaageing rate, per decade of hours
  • tttime since the last reflow
  • treft_{ref}referee time of the datasheet value
  • CminC_{min}effective capacitance of one part, worst case
  • CreqC_{req}capacitance your design needs
  • n, Nn,\,Nparts in parallel, and the fewest that meet Creq
More detail

DC bias

Class II ceramics lose capacitance as the DC voltage across them rises. How much depends on the part number, its case and its voltage rating, so read it from the maker's curve or tool at Vdc. C0G loses almost none.

Temperature

The class code bounds the change over its own temperature range: X5R and X7R ±15 %, X6S and X7S ±22 %, Y5V +22/−82 %, Z5U +22/−56 % (EIA-198). The page takes the minus side of that bound, which is measured with no DC bias, not this part's curve. C0G is 0 ± 30 ppm/°C about 25 °C.

Ageing

Class II ceramics lose capacitance with time at a steady rate per decade of hours, so 1 000 h to 10 000 h costs as much as 100 h to 1 000 h (Fiore). Datasheets give the value and tolerance at a referee time, 48 h or 1 000 h by part (KEMET), so the page counts no ageing before it. The clock starts at the last heating above the Curie point, about 120 °C (Fiore). Reflow goes above it, so count from the last reflow. C0G does not age.

Design to Cmin, the value left at the worst corner, not to the marked value.

Not modelled: the effect of the AC ripple voltage itself, and frequency.

References: EIA-198 temperature characteristic codes: X5R and X7R ±15 %; X6S and X7S ±22 %; Y5V +22/−82 %; Z5U +22/−56 %; C0G 0 ± 30 ppm/°C. KEMET multilayer ceramic capacitor datasheets: maximum ageing rate per decade hour, and value and tolerance indexed to a referee time of 48 h or 1 000 h. R. Fiore, Dielectric Aging Phenomena, American Technical Ceramics, Circuit Designer's Notebook: typical ageing rates, the log-decade law, and the clock's start at the last heating above the Curie point. Related: Decoupling & Bulk Capacitance, Buck Converter Design.

Engine version ⁨1.26.4⁩