The power dissipation PD of IC is expressed in the following equation.
PD = (VIN'-VOUT) IOUT + VIN' IB
If VIN' is reduced below the lowest voltage necessary for the IC, the parasitic oscillation will be caused according to circumstances.
In determining the resistance value of RSD, design with margin should be made by making reference to the following equation.
<VIN - VIN'
IOUT + IB
(4) Connect the input terminal and GND, and the output terminal and GND, by capacitor respectively.
The capacitances should be determined experimentally because they depend on printed patterns. In particular,
adequate investigation should be made so that there is no problem even at time of high or low temperature.
(5) Installation of IC for power supply
For obtaining high reliability on the heat sink design of the regulator IC, it is generally required to derate more than 20%
of maximum junction temperature (Tj MAX.) Further, full consideration should be given to the installation of IC to the heat sink.
(a) Heat sink design
The thermal resistance of IC itself is required from the viewpoint of the design of elements, but the thermal resistance from the
IC package to the open air varies with the contact thermal resistance. Table 1 shows how much the value of the contact thermal
resistance ( C + S) is changed by insulating sheet (mica) and heat sink grease.
0.3 0.5(1.5 2.0)
2.0 2.5(4.0 6.0)
The figures given in parentheses denote the values at time of no grease.
The package of regulator IC serves as GND, therefore, usually use the value at time of "no mica"
(b) Silicon grease
When a circuit not exceeding maximum rating is designed, it is to be desired that the grease should be used if possible.
If it is required that the contact thermal resistance is reduced from the view-point of the circuit design,
It is recommended that the following methods be adopted.
A: Use Thercon (Fuji High Polymer Kogyo K.K)
B: Use SC101 (Torei Silicon) or G-640 (GE), if grease is used.
When installing IC on a heat sink or the like, tighten the IC with the torque of less than the rated value. If it is tightened with
the torque in excess of the rated value, sometimes the internal elements of the IC are adversely affected. Therefore, great care
should be given to the installing operation. Further, if polycarbonate screws are used, the torque causes a change with the passage
of time, which may lessen the effect of radiation.
2010. 5. 19
Revision No : 1