CM1581 Datasheet, PDF (9/11 Pages) List of Unclassifed Manufacturers – 5A LOW DROPOUT VOLTAGE REGULATOR

CM1581
5A LOW DROPOUT VOLTAGE REGULATOR
Protection Diodes
In normal operation, CM1581 family does not need any protection diodes between the adjustment pin and the output and from the
output to the input to prevent die overstress. Internal resistors are limiting the internal current paths on the ADJ pin. Therefore
even with bypass capacitors on the adjust pin no protection diode is needed to ensure device safety under short-circuit conditions.
The Adjust pin can be driver on a transient basis ±7V with respect ti the output without any device degradation.
A protection diode between the Output pin and VPOWER pin is not usually needed. Microsecond surge currents of 50A to 100A can
be handled by the internal diode between the Output pin and VPOWER pin of the device. In normal operations, it is difficult to get
those values of surge currents even with the use of large output capacitances. Only with high value output capacitors, such as
1000uF to 5000uF and the VPOWER pin is instantaneously shorted to ground, damage an occur. A diode from output to input is
recommended (Figure 6). If CM1581 is connected as single supply device with the control and power input pins shorted together
the internal diode between the output and power input pin will protect the control input pin.
Thermal Consideration
The CM1581 adjustable version had internal power and thermal limiting circuitry (about 150℃) designed to protect the device
under overload conditions. However, maximum junction temperature ratings should not be exceeded under continuous normal
load conditions. Careful consideration must be given to all sources of thermal resistance from junction to ambient, including
junction-to-case, case-to-heatsink interface and heatsink resistance itself.
Junction temperature of the Control section can run up to 125℃. Junction temperature rise in the power transistor will be greater
than the temperature rise in the Control section making the thermal resistance lower in the Control section. At power levels below
12W, the temperature gradient will be lese than 25℃ and the maximum ambient temperature will be determined by the junction
temperature of the Control section. This is due to the lower maximum junction temperature in the Control section. At power levels
above 12W, the temperature gradient will be greater than 25℃ and the maximum ambient temperature will be determined by the
Power section. In both cases, the junction temperature is determined by the total power dissipated in the device. For most low
dropout applications the power dissipation will be less than 12W.
The power in the device us made up of two components: the power in the output transistor and the power in the control circuit.
The power in the control circuit is negligible, which is equal to: PCONTROL = (VCONTROL – VOUT)/ICONTROL, where ICONTROL is equal to
IOUT/100(typ)
The power in the output transistor is equal to: POUTPUT = (VPOWER – VOUT)/IOUT
The total power is equal to: PCONTROL + POUTPUT
Junction-to-case thermal resistance is specified from the IC junction to the bottom of the case directly below the die. This is the
lowest resistance path for the heat flow. In order to ensure the best possible thermal flow this area of the package to the heatsink
proper mounting is required. Thermal compound at the case-to-heatsink interface is recommended. A thermally conductive
spacer can be used, if the case of the device must be electrically isolated, but its added contribution to thermal resistance has to
be considered.
2002/02/05 Preliminary Rev. 1
Champion Microelectronic Corporation
Page 9