LT1963A Series
applicaTions inForMaTion
Y5Vdielectricsaregoodforprovidinghighcapacitancesin
asmallpackage,butexhibitstrongvoltageandtemperature
coefficients as shown in Figures 10 and 11. When used
with a 5V regulator, a 10µF Y5V capacitor can exhibit an
effective value as low as 1µF to 2µF over the operating
temperature range. The X5R and X7R dielectrics result in
more stable characteristics and are more suitable for use
as the output capacitor. The X7R type has better stability
across temperature, while the X5R is less expensive and
is available in higher values.
“FREE” Resistance with PC Traces
The resistance values shown in Table 2 can easily be made
using a small section of PC trace in series with the output
capacitor. The wide range of non-critical ESR makes it
easy to use PC trace. The trace width should be sized to
handle the RMS ripple current associated with the load.
Theoutputcapacitoronlysourcesorsinkscurrentforafew
microsecondsduringfastoutputcurrenttransitions.There
is no DC current in the output capacitor. Worst case ripple
current will occur if the output load is a high frequency
(>100kHz) square wave with a high peak value and fast
edges (< 1µs). Measured RMS value for this case is 0.5
times the peak-to-peak current change. Slower edges or
lower frequency will significantly reduce the RMS ripple
current in the capacitor.
Voltage and temperature coefficients are not the only
sources of problems. Some ceramic capacitors have a
piezoelectric response. A piezoelectric device generates
voltage across its terminals due to mechanical stress,
similar to the way a piezoelectric accelerometer or micro-
phone works. For a ceramic capacitor the stress can be
induced by vibrations in the system or thermal transients.
Table 2. PC Trace Resistors
10mΩ
20mΩ
30mΩ
"
"
"
0.5oz C
1.0oz C
2.0oz C
Width
0.011 (0.28mm)
0.011 (0.28mm)
0.011 (0.28mm)
U
U
U
"
"
"
Length
0.102 (2.6mm)
0.204 (5.2mm)
0.307 (7.8mm)
"
"
"
Width
Length
0.006 (0.15mm)
0.006 (0.15mm)
0.006 (0.15mm)
"
"
"
0.110 (2.8mm)
0.220 (5.6mm)
0.330 (8.4mm)
"
"
"
"
Width
Length
0.006 (0.15mm)
0.006 (0.15mm)
0.006 (0.15mm)
"
"
0.224 (5.7mm)
0.450 (11.4mm)
0.670 (17mm)
40
20
20
0
BOTH CAPACITORS ARE 16V,
1210 CASE SIZE, 10µF
X5R
X5R
0
–20
–40
–60
–80
–100
–20
–40
–60
–80
–100
Y5V
Y5V
BOTH CAPACITORS ARE 16V,
1210 CASE SIZE, 10µF
0
8
12 14
50
TEMPERATURE (°C)
100 125
2
4
6
10
16
–50 –25
0
25
75
DC BIAS VOLTAGE (V)
1963A F10
1963A F11
Figure 11. Ceramic Capacitor Temperature Characteristics
Figure 10. Ceramic Capacitor DC Bias Characteristics
1963aff
17
For more information www.linear.com/LT1963A
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