Three-terminal 3 A adjustable voltage regulators
Document overview
- Manufacturer or author: STMICROELECTRONICS
- PDF pages: 14
Technical content
Datasheet sections
- 1 Diagram
- 2 Pin configuration
- 3 Maximum ratings
- 4 Electrical characteristics
- 5 Typical performance
- 6 Application hints
- 6.1 External capacitors
- 6.2 Load regulation
- 6.3 Protection diodes
- 7 Application circuits
- 8 Package mechanical data
- 9 Revision history
Features
■ Guaranteed 3 A output current ■ Adjustable output down to 1.2 V ■ Line regulation typically 0.005 %/V ■ Load regulation typically 0.1 % ■ Guaranteed thermal regulation ■ Current limit constant with temperature ■ Standard 3-lead transistor package TO-3 Table 1. Device summary
1 Diagram
Figure 1. Schematic diagram
2 Pin configuration
Figure 2. Pin connections (bottom view)
3 Maximum ratings
Note: Absolute maximum ratings are those values beyond which damage to the device may occur. Table 2. Absolute maximum ratings Table 3. Thermal data
4 Electrical characteristics
Table 4. Electrical characteristics (VI -VO = 5V, IO = 1.5 A. Although power dissipation is internally
- Regulation is measured at constant j unction temperature. Changes in output voltage due to heating effects are taken into
account separately by thermal rejection.
5 Typical performance
Δ Needed if device is far from filter capacitors. Figure 3. 1.2 V to 25 V adjustable regulator
6 Application hints
current requirement. If there is insufficient load on the output, the output will rise.
6.1 External capacitors
values will eliminate the possibility of problems. paths and damaging the device. takes about 25 µF in aluminium electrolytic to equal 1 µF solid tantalum at high frequencies. Figure 4. Circuit
decrease in capacitance at frequencies around 0.5 MHz. For this reason, 0.01 µF disc may seem to work better than a 0.1 µF disc as a bypass. Although the LM350 is stable with no output capacitors, like any feedback circuit, certain values of external capacitance can cause excessive ringing. This occurs with values between 500 pF and 5000 pF . A 1 µF solid tantalum (or 25 µF aluminium electrolytic) on the output swamps this effect and insures stability.
6.2 Load regulation
The LM350 is capable of providing extremely good load regulation but a few precautions are needed to obtain maximum performance. The current set resistor connected between the adjustment terminal and the output terminal (usually 240 Ω) should be tied directly to the output of the regulator rather than near the load. This eliminates line drops from appearing effectively in series with the reference and degrading regulation. For example, a 15 V regulator with 0.05 Ω resistance between the regulator and load will have a load regulation due to line resistance of 0.05 Ω x I L. If the set resistor is connected near the load the effective line resistance will be 0.05 Ω (1 + R2/R1) or in this case, 11.5 times worse. Figure 5 shows the effect of resistance between the regulator and 140 Ω set resistor. With the TO-3 package, it is easy to minimize the resistance from the case to the set resistor, by using 2 separate leads to the case. The ground of R 2 can be returned near the ground of the load to provide remote ground sensing and improve load regulation.
6.3 Protection diodes
When external capacitors are used with any IC regulator it is sometimes necessary to add protection diodes to prevent the capacitors from discharging through low current points into the regulator. Most 20 µF capacitors have low enough internal series resistance to deliver 20 A spikes when shorted. Although the surge is short, there is enough energy to damage parts of the IC. When an output capacitor is connected to a regulator and the input is shorted, the output capacitor will discharge into the output of the regulator. The discharge current depends on the value of the capacitor, the output voltage of the regulator, and the rate of decrease of V In the LM350 this discharge path is through a large junction that is able to sustain 25 A surge with no problem. This is not true of other types of positive regulators. For output capacitors of 100 µF or less at output of 15 V or less, there is no need to use diodes. The bypass capacitor on the adjustment terminal can discharge through a low current junction. Discharge occurs when either the input or output is shorted. Internal to the LM350 is a 50 Ω resistor which limits the peak discharge current. No protection is needed for output voltages of 25 V or less and 10 µF capacitance. Figure 6 shows an LM350 with protection diodes included for use with outputs greater than 25 V and high values of output capacitance. Obsolete Product(s) - Obsolete Product(s)
7 Application circuits
Figure 5. Regulator with line resistance in output lead Figure 6. Regulator with protection diodes
8 Package mechanical data
In order to meet environmental requirements, ST offers these devices in ECOPACK® packages. These packages have a lead-free second level interconnect. The category of second Level Interconnect is marked on the package and on the inner box label, in compliance with JEDEC Standard JESD97. The maximum ratings related to soldering conditions are also marked on the inner box label. ECOPACK is an ST trademark. ECOPACK specifications are available at: www.st.com. Obsolete Product(s) - Obsolete Product(s)
Dim. mm. inch. A 11. 85 0.466 C 1.70 0.066 D 8.7 0. 342 E 20.0 0.7 87 G 10. 9 0.429 N 16. 9 0.665 P 26.2 1.0 31 R 3.88 4.09 0.152 0.161 U 39.5 1.555 V 30.10 1.1 85 TO-3 mechanical data P003C/C E B R C DAP G N VU O Obsolete Product(s) - Obsolete Product(s)
9 Revision history
Table 5. Document revision history 11-Feb-2008 2 Added: Table 1 on page 1.