Interfacing to Analog Switches Driving the Control Input of an Analog Switch with 1.8 V or Lower − Is it Safe? Application Note
■Analog switches are everywhere today. Due to their small size and low current consumption, they are popular in portable devices where they are effective in a variety of subsystems including audio and data communications, port connections, and even test. They can be used to facilitate signal routing, allow multiple data types to share an interface connector, or permit temporary access to internal processors during manufacturing. Analog switches are often used to give portable system designers a convenient method of increasing their features or accessibility without duplicating any circuitry. Understanding the key specifications and tradeoffs can make the difference between a temporary fix and a truly optimized solution.
●ON Semiconductor’s Solutions
■ON Semiconductor has developed a new control input buffer designed specifically to interface with low voltage chipsets. The new structure achieves two important goals − it lowers the minimum allowable VIH value that guarantees switching and maintains low leakage for the new expanded range of VIN values. Figure 7 shows leakage curves from ON Semiconductor’s NLAS5223BL. The graph shows the typical leakage current across VIN for three different switch VCC voltages − 2.7 V, 3.3 V, 4.2 V. It is clear that with the new structure the leakage current is significantly reduced fora wider range of VIH values. For example comparing the graphs in Figures 6 and 7, the leakage current for a VCC of 4.2 V and a VIH of 1.8 V is 450 μA for the original structure and 100 μA for the new structure, yielding a significant improvement.
■It is important to remember that even with the lower leakage values, there is still a limit to how low the VIH can safely operate. This goes back to the arguments made previously that the threshold voltage which defines the switch point varies with a number or parameters and a safety margin must be maintained in order to guarantee an effective switch. The VIH values specified in the datasheet take both factors into account. ON Semiconductor’s NLAS5223BL is designed to safely operate with VIH levels down to 1.6 V for VCC levels up to 4.3 V. In this scenario, a battery voltage that varies between 2.7 V and 4.2 V will never induce a leakage above 200 μA, typically much lower, when operated by a control input that toggles between ground and 1.6 V.
■ON Semiconductor’s portfolio of data and audio switches includes new devices designed to allow low baseband voltages, such as 1.8 V or lower, to drive the control input. The datasheet for each newly released device will include ICC leakage graphs for varying levels of VIN− giving the system designer a more complete picture of the tradeoffs and options available for interfacing to the switch. With this additional information, the designer is one step closer to an analog switch solution that is truly optimized for the application.
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[ portable devices ][ audio ][ data communications ] |
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Application note & Design Guide |
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Please see the document for details |
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English Chinese Chinese and English Japanese |
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March, 2017 |
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Rev. 2 |
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AND8304/D |
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127 KB |
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