LT1763 Series
APPLICATIONS INFORMATION
Y5VandZ5Ucapacitors,butcanstillbesignificantenough
todropcapacitorvaluesbelowappropriatelevels.Capacitor
DC bias characteristics tend to improve as component
casesizeincreases, butexpectedcapacitanceatoperating
voltage should be verified.
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:
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
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, especially when a ceramic
capacitor isusedfor noisebypassing. A ceramic capacitor
producedFigure6’straceinresponsetolighttappingfroma
pencil.Similarvibrationinducedbehaviorcanmasquerade
as increased output voltage noise.
1. Output current multiplied by the input/output voltage
differential: (I )(V – V ), and
OUT
IN
OUT
2. GND pin current multiplied by the input voltage:
(I )(V ).
GND
IN
The GND pin current can be found by examining the GND
Pin Current curves in the Typical Performance Character-
istics section. Power dissipation will be equal to the sum
of the two components listed above.
TheLT1763seriesregulatorshaveinternalthermallimiting
designedtoprotectthedeviceduringoverloadconditions.
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.
LT1763-5
C
C
LOAD
= 10μF
= 0.01μF
= 100mA
OUT
BYP
I
V
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.
OUT
500μV/DIV
1763 F06
100ms/DIV
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.
Figure 6. Noise Resulting from
Tapping on a Ceramic Capacitor
Table 1. DE Package, 12-Lead DFN
COPPER AREA
THERMAL RESISTANCE
BOARD AREA (JUNCTION-TO-AMBIENT)
TOPSIDE* BACKSIDE
2
2
2
2
2
2
2500mm
2500mm
2500mm
2500mm
2500mm
2500mm
2500mm
2500mm
2500mm
40°C/W
45°C/W
50°C/W
60°C/W
2
2
2
2
1000mm
2
225mm
100mm
2
* Device is mounted on topside
1763fe
16
Linear [ Linear ]
