lt1763cs8-trpbf Linear Technology Corporation, lt1763cs8-trpbf Datasheet - Page 15

• Manufacturer Part Number: lt1763cs8-trpbf
• Description: 500ma, Low Noise, Ldo Micropower Regulators
• Manufacturer: Linear Technology Corporation

APPLICATIONS
significant enough to drop capacitor values below appro-
priate levels. Capacitor DC bias characteristics tend to
improve as component case size increases, but expected
capacitance at operating voltage should be verified.
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.
The resulting voltages produced can cause appreciable
amounts of noise, especially when a ceramic capacitor is
used for noise bypassing. 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.
500µV/DIV
V
OUT
Figure 6. Noise Resulting from Tapping
on a Ceramic Capacitor
LT1763-5
C
C
I
LOAD
OUT
BYP
= 0.01µf
= 10µF
= 100mA
U
INFORMATION
100ms/DIV
U
W
1763 F06
U
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 made up of two
components:
1. Output current multiplied by the input/output voltage
2. GND pin current multiplied by the input voltage:
The GND pin current can be found by examining the GND
Pin Current curves in the Typical Performance Character-
istics. Power dissipation will be equal to the sum of the two
components listed above.
The LT1763 series regulators have internal thermal limit-
ing designed to protect the device during overload condi-
tions. For continuous normal conditions, the maximum
junction temperature rating of 125°C must not be
exceeded. It is important to give careful consideration to
all sources of thermal resistance from junction to ambient.
Additional heat sources mounted nearby must also be
considered.
For surface mount devices, heat sinking is accomplished
by using the heat spreading capabilities of the PC board
and its copper traces. Copper board stiffeners and plated
through-holes can also be used to spread the heat gener-
ated by power devices.
The following tables list thermal resistance for several
different board sizes and copper areas. All measurements
were taken in still air on 3/32" FR-4 board with one ounce
copper.
Table 1. SO-8 Package, 8-Lead SO
* Device is mounted on topside
TOPSIDE*
2500mm
1000mm
225mm
100mm
50mm
differential: (I
(I
GND
COPPER AREA
2
)(V
2
2
2
2
IN
BACKSIDE
2500mm
2500mm
2500mm
2500mm
2500mm
).
OUT
2
2
2
2
2
)(V
IN
BOARD AREA (JUNCTION-TO-AMBIENT)
2500mm
2500mm
2500mm
2500mm
2500mm
– V
OUT
2
2
2
2
2
LT1763 Series
), and
THERMAL RESISTANCE
60°C/W
60°C/W
68°C/W
74°C/W
86°C/W
15
1763fc