Datasheet

LT1964
10
1964f
Figure 2. Ceramic Capacitor DC Bias Characteristics
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
differential: I
OUT
• (V
IN
– V
OUT
), and
2. Ground pin current multiplied by the input voltage:
I
GND
• V
IN
.
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 LT1964 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 table lists 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. Measured Thermal Resistance
COPPER AREA THERMAL RESISTANCE
TOPSIDE* BACKSIDE BOARD AREA (JUNCTION-TO-AMBIENT)
2500mm
2
2500mm
2
2500mm
2
125°C/W
1000mm
2
2500mm
2
2500mm
2
125°C/W
225mm
2
2500mm
2
2500mm
2
130°C/W
100mm
2
2500mm
2
2500mm
2
135°C/W
50mm
2
2500mm
2
2500mm
2
150°C/W
*Device is mounted on topside.
The thermal resistance junction-to-case (θ
JC
), measured
at Pin 2, is 60°C/W.
DC BIAS VOLTAGE (V)
CHANGE IN VALUE (%)
1964 F02
20
0
–20
–40
–60
–80
–100
0
4
8
10
26
12
14
X5R
Y5V
16
BOTH CAPACITORS ARE 16V,
1210 CASE SIZE, 10µF
TEMPERATURE (°C)
–50
40
20
0
–20
–40
–60
–80
–100
25 75
1964 F03
–25 0
50 100 125
Y5V
CHANGE IN VALUE (%)
X5R
BOTH CAPACITORS ARE 16V,
1210 CASE SIZE, 10µF
APPLICATIO S I FOR ATIO
WUU
U
Figure 3. Ceramic Capacitor Temperature Characteristics
Figure 4. Noise Resulting from Tapping on a Ceramic Capacitor
LT1964-5
C
OUT
= 10µF
C
BYP
= 0.01µF
I
LOAD
= –200mA
V
OUT
1mV/DIV
100ms/DIV
1964 F04