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LP3982IMM-3.0 Datasheet(PDF) 7 Page - Texas Instruments |
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LP3982IMM-3.0 Datasheet(HTML) 7 Page - Texas Instruments |
7 / 23 page O 1 2 V R R 1 1.25V é ù = - ê ú ë û VO = VREF R1 R2 + 1 OFF THERMAL PROTECTION 1.25V BANDGAP FAST START-UP CIRCUIT CURRENT LIMIT FAULT COMPARATORS R1 R2 VIN VO SET CC SHDN FAULT GND ERROR AMP + - LP3982 www.ti.com SNVS185D – FEBRUARY 2002 – REVISED APRIL 2013 APPLICATION INFORMATION General Information The LP3982 is package, pin and performance compatible with Maxim's MAX8860 excluding reverse battery protection and Dual Mode function (fixed and adjustable combined). Figure 16 shows the functional block diagram for the LP3982. A 1.25V bandgap reference, an error amplifier and a PMOS pass transistor perform voltage regulation while being supported by shutdown, fault, and the usual Temperature and current protection circuitry The regulator's topology is the classic type with negative feedback from the output to one of the inputs of the error amplifier. Feedback resistors R1 and R2 are either internal or external to the IC, depending on whether it is the fixed voltage version or the adjustable version. The negative feedback and high open loop gain of the error amplifier cause the two inputs of the error amplifier to be virtually equal in voltage. If the output voltage changes due to load changes, the error amplifier provides the appropriate drive to the pass transistor to maintain the error amplifier's inputs as virtually equal. In short, the error amplifier keeps the output voltage constant in order to keep its inputs equal. Figure 16. Functional Block Diagram for the LP3982 Output Voltage Setting (Adj Version Only) The output voltage is set according to the amount of negative feedback (Note that the pass transistor inverts the feedback signal.) Figure 17 simplifies the topology of the LP3982. This type of regulator can be represented as an op amp configured as non-inverting amplifier and a fixed DC Voltage (VREF) for its input signal. The special characteristic of this op amp is its extra-large output transistor that only sources current. In terms of its non- inverting configuration, the output voltage equals VREF times the closed loop gain: (1) Utilize the following equation for adjusting the output to a particular voltage: (2) Choose R2 = 100k to optimize accuracy, power supply rejection, noise and power consumption. Copyright © 2002–2013, Texas Instruments Incorporated Submit Documentation Feedback 7 Product Folder Links: LP3982 |
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