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Additional copper area improves the thermal characteristicsbut with copper areas greater than approximately 6 in 2only small improvements in heat dissipation are realized. The PC board copper area that the package is soldered to should be at least 0. For best results, external components should be located as close to the switcher IC as possible using ground plane construction or single point grounding.
Rapidly switching currents associated with wiring inductance can generate voltage transients which can cause problems. When using the adjustable version, special care must be taken as to datashewt location of the feedback resistors and the associated wiring. Wiring inductance, stray capacitance, as well as the scope probe used to evaluate these transients, all contribute to the amplitude datasheeet these spikes.
This is a stress rating only and functional operation of the device at these or any other conditions above those indicated in the operation is not implied. Large areas of copper provide the best transfer of heat lower thermal resistance to the surrounding air, and moving air lowers the thermal resistance even further.
These temperature rise numbers are all approximate and there are many factors that can affect these temperatures. The TD TO package junction temperature rise above ambient temperature with a 3A load for various input and output voltages.
Symbol Parameter Conditions Min. This data was taken with the circuit operating as a buck switching regulator with all components mounted on datashete PC board to simulate the junction temperature under actual operating conditions.
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Quiescent Current vs Temperature Figure 9. Higher ambient temperatures require more heat sinking. Self protection features include a two stage frequency reducing current limit for the output switch and an over temperature shutdown for complete protection under fault conditions. If open core inductors are used, special care must be taken as to the location and positioning of this type of inductor.
The TD junction temperature rises above ambient temperature for a 3A load and different input and output voltages. It is capable of driving a 3A load with excellent line and load regulation. The voltage spikes are present because of the fast datzsheet action of the output switch, and the parasitic inductance of the output filter capacitor, To minimize these voltage spikes, special low inductance capacitors can be used, dattasheet their lead lengths must be kept short.
Exposure to absolute maximum rating conditions for extended periods may affect reliability. For the best thermal performance, wide copper traces and generous amounts of printed circuit board copper should be used in the board layout.
The TO surface mount package tab is designed to be soldered to the copper on a printed circuit board.
Output Saturation Characteristics Figure 7. This curve can be used for a quick check for the approximate junction temperature for various conditions, but be aware that there are many factors that can affect the junction temperature. The copper and the board are the heat sink for this package and the other heat producing components, such as the catch diode and inductor.
Typical Performance Characteristics Figure 4. The device is available in an adjustable or fixed output version. Pulling this pin below a threshold voltage of approximately 1. A suitable input bypass capacitor must be present at this pin to minimize voltage transients and to supply the switching currents needed by the regulator.
Once exception to this is the output switch pin, which should not have large areas of copper. To minimize coupling to sensitive circuitry, the PC board copper area connected to this pin should be kept a minimum.
1N58xx Schottky diodes
The size of the heatsink depends on the input voltage, the output voltage, the load current and the ambient temperature. Stresses greater than those listed under Maximum Ratings may cause permanent damage to the device. Physically locate both resistors near the IC, and route the wiring away form the inductor especially an open core type of inductor. Requiring a minimum number of external components, these regulators are on5821 to use and include internal frequency compensation, and a fixed-frequency oscillator.
As in any switching regulator, layout is very important. An additional small LC filter can be added to the output as shown in Figure 14 to further reduce the amount of output ripple and transients. The output ripple voltage is due mainly to the inductor sawtooth ripple current multiplied by the ESR of the output capacitor. Feedback Senses the regulated output voltage to complete the feedback loop.