TLE2682 Datasheet, PDF (48/49 Pages) Texas Instruments – HIGH-SPEED JFET-INPUT DUAL OPERATIONAL AMPLIFIER WITH SWITCHED-CAPACITOR VOLTAGE CONVERTER

TLE2682
HIGHĆSPEED JFETĆINPUT DUAL OPERATIONAL AMPLIFIER
WITH SWITCHEDĆCAPACITOR VOLTAGE CONVERTER
SLOS127 − JUNE 1993
APPLICATION INFORMATION
power dissipation (continued)
The factor of 1.3 allows some operating margin for the TLE2682.
When using a 12-V to − 5-V converter at 100-mA output current, calculate the power dissipation without an
external resistor:
P + (12 V * | * 5 V | ) (100 mA) ) (12 V) (100 mA) (0.2)
(8)
P + 700 mW ) 240 mW + 940 mW
+COUT
C1
+
1
1 OUT
2
1 IN −
3
1 IN +
VOUT
R2
R1
4
VCC _−
5
VOUT
6
VREF
7
OSC
8
VIN
+
VIN
16
VCC +
15
2 OUT
14
2 IN −
13
2 IN +
12
CAP −
11
GND
10
CAP +
9
FB/SD
CIN
+
Rx
Figure 106. Power-Dissipation-Limiting Resistor in Series With C_IN
At θ_JA of 130°C/W for a commercial plastic device, a junction temperature rise of 122°C is seen. The device
exceeds the maximum junction temperature at an ambient temperature of 25°C. To calculate the power
dissipation with an external resistor (R_X), determine how much voltage can be dropped across R_X. The
maximum voltage loss of the TLE2682 in the standard regulator configuration at 100 mA output current is 1.6 V.
VX + 12 V * [(1.6 V) (1.3) ) | * 5 V | ] + 4.9 V and
(9)
RX + 4.9 Vń(4.4) (100 mA) + 11 W
The resistor reduces the power dissipated by the TLE2682 by (4.9 V) (100 mA) = 490 mW. The total power
dissipated by the TLE2682 is equal to (940 mW − 490 mW) = 450 mW. The junction temperature rise is 58°C.
Although commercial devices are functional up to a junction temperature of 125°C, the specifications are tested
to a junction temperature of 100°C. In this example, this means limiting the ambient temperature to 42°C. To
allow higher ambient temperatures, the thermal resistance numbers for the TLE2682 packages represent
worst-case numbers with no heat-sinking and still air. Small clip-on heat sinks can be used to lower the thermal
resistance of the TLE2682 package. Airflow in some systems helps to lower the thermal resistance. Wide PC
board traces from the TLE2682 leads help to remove heat from the device. This is especially true for plastic
packages.
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