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LT1020CSW Datasheet(PDF) 7 Page - Linear Technology |
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LT1020CSW Datasheet(HTML) 7 Page - Linear Technology |
7 / 16 page 7 LT1020 sn1020 1020fcs The LT1020 is especially suited for micropower system applications. For example, the comparator section of the LT1020 may be used as a battery checker to provide an indication of low battery. The dropout detector can shut down the system when the battery voltage becomes too low to regulate. Another type of system application for the LT1020 would be to generate the equivalent of split supplies from a single power input. The regulator section provides regulated output voltage and the reference, which can both source and sink current, is then an artificial system ground providing a split supply for the system. For many applications the comparator can be frequency compensated to operate as an amplifier. Compensation values for various gains are given in the data sheet. The comparator gain is purposely low to make it easier to frequency compensate as an amplifier. Two outputs are available on the comparator, the NPN output is capable of sinking 10mA and can drive loads connected to voltages in excess of the positive power supply. This is useful for driving switches or linear regulators from a higher input voltage. The PNP output, which is capable of sourcing 100 µA can drive loads below ground. It can be used to make negative regulators with the addition of an external pass transistor. Both outputs can be tied together to provide an output that swings from rail-to-rail for com- parator or amplifier applications. Although it is not speci- fied, the gain for the PNP output is about 500 to 1000. If the PNP output is being used, to maximize the gain a 1 µA to 5 µA load should be placed upon the NPN output collector. This is easily done by connecting a resistor between the NPN collector and the reference output. (Providing this operating current to the NPN side in- creases the internal emitter base voltages and maximizes the gain of the PNP stage.) Without this loading on the NPN collector, at temperatures in excess of 75 °C, the gain of the PNP collector can decrease by a factor of 2 or 3. Reference Internal to the LT1020 is a 2.5V trimmed class B output reference. The reference was designed to be able to source or sink current so it could be used in supply splitting applications as well as a general purpose reference for external circuitry. The design of the reference allows it to source typically 4mA or 5mA and sink 2mA. The available source and sink current decreases as temperature in- creases. It is sometimes desirable to decrease the AC output impedance by placing an output capacitor on them. The reference in the LT1020 becomes unstable with large capacitive loads placed directly on it. When using an output capacitor, about 20 Ω should be used to isolate the capacitor from the reference pin. This 20 Ω resistor can be placed directly in series with the capacitor or alternatively the reference line can have 20 Ω placed in series with it and then a capacitor to ground. This is shown in Figure 1. Other 7 8 3 13 11 2 9 REF 2.5V REF OUT CURRENT LIMIT VIN VOUT DROPOUT DETECTOR FB GND INVERTING NON- INVERTING NPN OUT PNP OUT 10 4 1020 BD – + 6 5 BLOCK DIAGRA APPLICATIO S I FOR ATIO |
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