CM2576 Datasheet, PDF (10/12 Pages) Champion Microelectronic Corp. – 3A STEP DOWN VOLTAGE REGULATOR

CM2576
3A STEP DOWN VOLTAGE REGULATOR
An inductor should not be operated beyond its maximum rated current because it may saturate. When an inductor begins to
saturate, the inductance decreases rapidly and the inductor begins to look mainly resistive (the DC resistance of the winding).
This will cause the switch current to rise very rapidly. Different inductor types have different saturation characteristics, and this
should be well considered when selecting as inductor.
Feedback Connection
For fixed output voltage version, the FB (feedback) pin must be connected to VOUT. For the adjustable version, it is important to
place the output voltage ratio resistors near CM2576 as possible in order to minimize the noise introduction.
ENABLE
It is required that the ENABLE must not be left open. For normal operation, connect this pin to a “LOW” voltage (typically, below
1.6V). On the other hand, for standby mode, connect this pin with a “HIGH” voltage. This pin can be safely pulled up to +VIN
without a resistor in series with it.
Grounding
To maintain output voltage stability, the power ground connections must be low-impedance. For the 5-lead TO-220 and TO-263
style package, both the tab and pin 3 are ground and either connection may be used.
Heatsink and Thermal Consideration
Although the CM2576 requires only a small heatsink for most cases, the following thermal consideration is important for all
operation. With the package thermal resistances θJA and θJC, total power dissipation can be estimated as follows:
PD = (VIN x IQ) + (VOUT / VIN)(ILOAD x VSAT);
When no heatsink is used, the junction temperature rise can be determined by the following:
∆TJ = PD x θJA;
With the ambient temerpature, the actual junction temperature will be:
TJ = ∆TJ + TA;
If the actual operating junction temperature is out of the safe operating junction temperature (typically 125℃), then a heatsink is
required. When using a heatsink, the junction temperature rise will be reduced by the following:
∆TJ = PD x (θJC + θinterface + θHeatsink);
Also one can see from the above, it is important to choose an heatsink with adequate size and thermal resistance, such that to
maintain the regulator’s junction temperature below the maximum operating temperature.
2003/08/07 Preliminary Rev. 1.1
Champion Microelectronic Corporation
Page 10