lt1963aes8-trpbf Linear Technology Corporation, lt1963aes8-trpbf Datasheet - Page 14

• Manufacturer Part Number: lt1963aes8-trpbf
• Description: 1.5a, Low Noise, Fast Transient Response Ldo Regulators
• Manufacturer: Linear Technology Corporation

LT1963A Series
APPLICATIO S I FOR ATIO
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.
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.
“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
14
Figure 10. Ceramic Capacitor DC Bias Characteristics
–100
–20
–40
–60
–80
20
0
0
2
Table 2. PC Trace Resistors
0.5oz C
1.0oz C
2.0oz C
U
4
DC BIAS VOLTAGE (V)
BOTH CAPACITORS ARE 16V,
1210 CASE SIZE, 10µF
U
U
U
6
U
8
Width
Length
Width
Length
Width
Length
Y5V
X5R
10
12
W
14
1963 F10
0.011
0.006
0.006
0.102
0.110
0.224
16
10mΩ
"
"
"
"
"
"
(0.28mm)
(0.15mm)
(0.15mm)
U
(2.6mm)
(2.8mm)
(5.7mm)
easy to use PC trace. The trace width should be sized to
handle the RMS ripple current associated with the load.
The output capacitor only sources or sinks current for a
few microseconds during fast output current transitions.
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.
This resistor should be made using one of the inner
layers of the PC board which are well defined. The resis-
tivity is determined primarily by the sheet resistance of the
copper laminate with no additional plating steps. Table 2
gives some sizes for 0.75A RMS current for various
copper thicknesses. More detailed information regarding
resistors made from PC traces can be found in Application
Note 69, Appendix A.
0.011
0.006
0.006
0.450
Figure 11. Ceramic Capacitor Temperature Characteristics
0.204
0.220
20mΩ
"
"
"
"
"
"
(0.28mm)
(0.15mm)
(0.15mm)
(11.4mm)
(5.2mm)
(5.6mm)
–100
–20
–40
–60
–80
40
20
0
–50
BOTH CAPACITORS ARE 16V,
1210 CASE SIZE, 10µF
–25
0
TEMPERATURE (°C)
0.011
0.006
0.006
0.307
0.330
0.670
25
30mΩ
"
"
"
"
"
"
(0.28mm)
(0.15mm)
(0.15mm)
(7.8mm)
(8.4mm)
(17mm)
50
Y5V
75
X5R
100
1963 F11
125
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