LP2980-N

SNOS733M – APRIL 2000 – REVISED JUNE 2013

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Figure 41. 5V to 3.3V @ 3A Converter

With limited input voltage range, the LP2980-N can control a 3.3V, 3A regulator with the use of a high current-

gain external PNP pass transistor as shown in Figure 41. If the regulator is to be loaded with the full 3A, heat

sinking will be required on the pass transistor to keep it within its rated temperature range. Refer to Figure 42 .

For best load regulation at the high load current, the LP2980-N output voltage connection should be made as

close to the load as possible.

Although this regulator can handle a much higher load current than can the LP2980-N alone, it can be shut down

in the same manner as the LP2980-N. When the ON/OFF control is brought low, the converter will be in

shutdown, and will draw less than 1

μA from the source.

Notes:

1. Drive this input with a logic signal (see APPLICATION HINTS). If the shutdown function is not to be used, tie

2. Capacitor is required for regulator stability. Minimum size is shown, and may be increased without limit.

3. Increasing the output capacitance improves transient response and increases phase margin.

4. A heatsink may be required for this transistor. The maximum allowable value for thermal resistance of the

heatsink is dependent on ambient temperature and load current (see curves in Figure 42). Once the value is

obtained from the graph, a heatsink must be selected which has a thermal resistance equal to or lower than

this value. If the value is above 60°C/W, no heatsink is required (the TO-220 package alone will safely

dissipate this).

For these curves, a maximum junction temperature of 150°C is assumed for the pass transistor. The case-to-

heatsink attachment thermal resistance is assumed to be 1.5°C/W. All calculations are for 5.5V input voltage

(which is worst-case for power dissipation).

Figure 42. Heatsink Thermal Resistance Requirements for Figure 41

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