LT1054 Datasheet, PDF (14/26 Pages) Linear Technology – Switched-Capacitor Voltage Converter with Regulator

LT1054
SWITCHEDĆCAPACITOR VOLTAGE CONVERTERS
WITH REGULATORS
SLVS033F − FEBRUARY 1990 − REVISED NOVEMBER 2004
APPLICATION INFORMATION
power dissipation (continued)
At R_θJA of 130°C/W for a commercial plastic device, a junction temperature rise of 122°C occurs. 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 LT1054 in the standard regulator configuration at 100 mA output current is 1.6 V.
V_X + 12 V * [(1.6 V)(1.3) ) |*5 V|] + 4.9 V
(10)
and
R_X
+
4.9 V
(4.4)(100 mA)
+
11
W
(11)
The resistor reduces the power dissipated by the LT1054 by (4.9 V)(100 mA) = 490 mW. The total power
dissipated by the LT1054 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 LT1054 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 LT1054 package. Airflow in some systems helps to lower the thermal resistance. Wide printed
circuit board traces from the LT1054 leads help remove heat from the device. This is especially true for plastic
packages.
1N4002 ^{100 kΩ}
10 µF ₊
−
+
+
−
1N5817
Tach
Motor
10 V
1
FB/SD
VCC ⁸
2
CAP+
7
OSC
3
GND
LT1054
6
VREF
+
5 µF
4
CAP−
VOUT ⁵
NOTE: Motor-Tach is Canon CKT26-T5-3SAE.
Pin numbers shown are for the P package.
Figure 18. Motor-Speed Servo
100-kΩ
Speed Control
14
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