lt3092 Linear Technology Corporation, lt3092 Datasheet - Page 11

• Manufacturer Part Number: lt3092
• Description: 200ma Two-terminal Programmable Current Source
• Manufacturer: Linear Technology Corporation

APPLICATIONS INFORMATION
ter performance than found in these tables. Demo circuit
1531A’s board layout using multiple inner V
multiple thermal vias achieves TBD°C/W performance for
the DFN package.
Table 2. DD Package, 8-Lead DFN
*Device is mounted on topside
Table 3. TS8 Package, 8-Lead SOT-23
Table 4. ST Package, 3-Lead SOT-223
*Device is mounted on topside
For further information on thermal resistance and using thermal information,
refer to JEDEC standard JESD51, notably JESD51-12.
Calculating Junction Temperature
Example: Given an industrial factory application with an
input voltage of 15V ±10%, an output voltage of 12V ±5%,
an output current of 200mA and a maximum ambient
temperature of 50°C, what would be the maximum junc-
tion temperature for a DFN package?
The total circuit power equals:
The SET pin current is negligible and can be ignored.
*Device is mounted on topside
TOPSIDE*
TOPSIDE*
TOPSIDE*
2500mm
1000mm
2500mm
1000mm
2500mm
1000mm
225mm
100mm
225mm
100mm
225mm
100mm
P
TOTAL
COPPER AREA
COPPER AREA
COPPER AREA
2
2
2
2
2
2
2
2
2
2
2
2
= (V
BACKSIDE
BACKSIDE
BACKSIDE
2500mm
2500mm
2500mm
2500mm
2500mm
2500mm
2500mm
2500mm
2500mm
2500mm
2500mm
2500mm
IN
– V
2
2
2
2
2
2
2
2
2
2
2
2
OUT
BOARD AREA
BOARD AREA
BOARD AREA
)(I
2500mm
2500mm
2500mm
2500mm
2500mm
2500mm
2500mm
2500mm
2500mm
2500mm
2500mm
2500mm
OUT
)
2
2
2
2
2
2
2
2
2
2
2
2
(JUNCTION-TO-AMBIENT)
(JUNCTION-TO-AMBIENT)
(JUNCTION-TO-AMBIENT)
THERMAL RESISTANCE
THERMAL RESISTANCE
THERMAL RESISTANCE
TBD°C/W
TBD°C/W
TBD°C/W
TBD°C/W
TBD°C/W
TBD°C/W
TBD°C/W
TBD°C/W
TBD°C/W
TBD°C/W
TBD°C/W
TBD°C/W
OUT
planes and
V
V
I
Power dissipation under these conditions equals:
Junction temperature equals:
In this example, the junction temperature is below the
maximum rating, ensuring reliable operation.
Protection Features
The LT3092 incorporates several protection features ideal
for battery-powered circuits, among other applications.
In addition to normal circuit protection features such as
current limiting and thermal limiting, the LT3092 protects
itself against reverse-input voltages, reverse-output volt-
ages, and reverse OUT-to-SET pin voltages.
Current limit protection and thermal overload protection
protect the IC against output current overload condi-
tions. For normal operation, do not exceed a junction
temperature of 125°C. The thermal shutdown circuit’s
typical temperature threshold is 165°C and has about
5°C of hysteresis.
The LT3092’s IN pin withstands ±40V voltages with respect
to the SET and OUT pins. Reverse-current fl ow, if OUT is
greater than IN, is less than 1mA (typically under 100μA),
protecting the LT3092 and sensitive loads.
Clamping diodes and 1k limiting resistors protect the
LT3092’s SET pin relative to the OUT pin voltage. These
protection components typically only carry current under
transient overload conditions. These devices are sized to
handle ±10V differential voltages and ±15mA crosspin
current fl ow without concern. Two immediate scenarios
present themselves for these application concerns. The
fi rst scenario employs a noise-reducing SET pin bypass
capacitor while OUT is instantaneously shorted to GND. The
second scenario follows improper shutdown techniques
in which the SET pin is quickly reset to GND while OUT is
held up by a large output capacitance with light load.
OUT
IN(MAX CONTINUOUS)
OUT(MIN CONTINUOUS)
P
T
T
TOTAL
J
J
= 200mA
= T
= 50°C + (1.02W • 60°C/W) = 111.2°C
A
= (16.5 – 11.4V)(200mA) = 1.02W
+ P
TOTAL
• θ
= 16.5 (15V + 10%)
= 11.4V (12V – 5%)
JA
LT3092
11
3092p