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SG29085AP Datasheet(PDF) 4 Page - Microsemi Corporation |
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SG29085AP Datasheet(HTML) 4 Page - Microsemi Corporation |
4 / 4 page SG29085/85A 12/90 Rev 1.1 2/94 LINFINITY Microelectronics Inc. Copyright © 1994 11861 Western Avenue ∞ ∞ ∞ ∞ ∞ Garden Grove, CA 92841 4 (714) 898-8121 ∞ ∞ ∞ ∞ ∞ FAX: (714) 893-2570 APPLICATION HINTS EXTERNAL CAPACITORS To stabilize the outputs and prevent oscillation (perhaps by many volts) external capacitors are required. The minimum recom- mended value for the output capacitors is 10µF, although the actual size and type will likely vary according to the particular application, e.g., operating temperature range and load. Another consideration is the effective series resistance (ESR) of the capacitor. Capacitor ESR will vary by manufacturer. Conse- quently, some evaluation may be required to determine the minimum value of the output capacitors. Generally worst case occurs at the maximum load and minimum ambient temperature. The size of the output capacitor can be increased to any value above the minimum. One possible advantage of this would be to maintain the output voltage during brief periods of negative input transients The output capacitors chosen should be rated for the full range of ambient temperature over which the circuit will be exposed and expected to operate. For example, many aluminum type electro- lytic capacitors will freeze at -30°C. The effective capacitance is reduced to zero in such a situation. Capacitors rated for -40°C operation must be used in order to maintain regulator stability at that temperature. Tantalum capacitors satisfy this requirement. STANDBY OUTPUT The SG29085/85A differs from most fixed voltage regulators in that it is equipped with two regulator outputs instead of one. The additional output is intended for use in systems requiring standby memory circuits. While the high current regulator output can be controlled with the ON/OFF pin described below, the standby remains on under all conditions as long as sufficient input voltage is applied to the IC. Thus, memory and other circuits powered by this output remain unaffected by positive line transients, thermal shutdown, etc. The standby regulator circuit is designed so that the quiescent current to the IC is very low (<1.5mA) when the other regulator output is off. If the standby output is not required it can be disabled. This is accomplished by connecting a resistor from the standby output to the supply voltage, thereby also eliminating the requirement for a more expensive output capacitor to prevent unwanted oscilla- tions. The resistor value depends upon the minimum input voltage expected for a given system. Since the standby output is shunted with an internal 5.6V zener, the current through the external resistor should be sufficient to bias internal resistors up to this point. Approximately 60 µA will suffice, resulting in a 10k external resistor for most applications (Figure 1). HIGH CURRENT OUTPUT 5-PIN TO-220 PLASTIC P - PACKAGE Ambient Temperature Range SG29085P -40 °C to 85°C SG29085AP -40 °C to 85°C Part No. Package Connection Diagram 5 STANBY OUTPUT 4 ON/OFF SWITCH 3 GROUND 2 OUTPUT VOLTAGE (V OUT) 1 INPUT VOLTAGE (V IN) GND CONNECTION DIAGRAM & ORDERING INFORMATION (See Note Below) STANDBY OUTPUT V IN R D 10K C3 FIGURE 1. Disabling Standby Output to Eliminate C3 SG29085/85A The high current regulated output features fault protection against overvoltage as well as a thermal shutdown feature. If the input voltage rises above 33V (load dump), the high current output shuts down automatically. The internal circuitry is thus protected and the IC is able to survive higher voltage transients than might otherwise be expected. The thermal shutdown of the high current output effectively guards against overheating of the die since this section of the IC is the principle source of power dissipation on the chip. ON/OFF SWITCH The ON/OFF pin is a high impedance low current switch that controls the main output voltage (pin 2). This is directly compat- ible with all 5 volt logic families. For use with open collector logic outputs, a 100Kresistor from this pin to a 5V supply, such as Pin 5, is required. Note: 1. All packages are viewed from the top. |
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