LTC1844-1.5 LINER [Linear Technology], LTC1844-1.5 Datasheet - Page 8

• Manufacturer Part Number: LTC1844-1.5
• Description: 150mA, Micropower, Low Noise, VLDO Linear Regulator
• Manufacturer: LINER [Linear Technology]

LTC1844 Series
APPLICATIONS
temperature and applied voltage. The most common di-
electrics used are Z5U, Y5V, X5R and X7R. The Z5U and
Y5V dielectrics are good for providing high capacitances
in a small package, but exhibit strong voltage and tem-
perature coefficients as shown in Figures 4 and 5. When
used with a 5V regulator, a 10 F Y5V capacitor can exhibit
an effective value as low as 1 F to 2 F 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.
8
Figure 5. Ceramic Capacitor Temperature Characteristics
Figure 4. Ceramic Capacitor DC Bias Characteristics
–100
–100
–20
–40
–60
–80
–20
–40
–60
–80
40
20
20
0
0
–50
0
BOTH CAPACITORS ARE 16V,
1210 CASE SIZE, 10 F
–25
2
U
4
DC BIAS VOLTAGE (V)
0
TEMPERATURE ( C)
BOTH CAPACITORS ARE 16V,
1210 CASE SIZE, 10 F
6
INFORMATION
25
U
8
Y5V
X5R
50
10
Y5V
75
12
W
X5R
100
14
1844 F05
1844 F04
125
16
U
Additionally, 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 microphone works. For a
ceramic capacitor the stress can be induced by vibrations
in the system or thermal transients. The resulting voltages
produced can cause appreciable amounts of noise, espe-
cially when a ceramic capacitor is used for noise bypass-
ing. A ceramic capacitor produced Figure 6’s trace in
response to light tapping from a pencil. Similar vibration-
induced behavior can masquerade as increased output
voltage noise.
Thermal Considerations
The power handling capability of the device will be limited
by the maximum rated junction temperature (125 C). The
power dissipated by the device will be the output current
multiplied by the input/output voltage differential:
(I
The LTC1844 series regulators have internal thermal lim-
iting designed to protect the device during momentary
overload conditions. For continuous normal conditions,
the maximum junction temperature rating of 125 C must
not be exceeded. It is important to give careful consider-
ation to all sources of thermal resistance from junction to
ambient. Additional heat sources mounted nearby must
also be considered.
Figure 6. Noise Resulting from Tapping on a Ceramic Capacitor
OUT
500 V/DIV
)(V
V
OUT
IN
– V
LTC1844-2.8
C
C
I
LOAD
OUT
BYP
OUT
= 0.01 F
= 10 F
= 100mA
).
100ms/DIV
1844 F06
1844ia