NLAS4717 Analog Switch Permits USB 1.1 Switching APPLICATION NOTE

PublishTime：2022-05-16

●On Semiconductor has introduced a new low resistance analog switch suitable for interfacing with USB 1.1 (USB2.0 Full Speed). The switch is completely bi−lateral and maybe used to carry either digital or analog signals. The NLAS4717 is a dual Single Pole Double Throw (SPDT) switch capable of switching either two independent signals or a differential signal pair as with USB.
●The USB 2.0 specification, completed in 2000, has now become the mainstay of peripheral connections. This specification fully encompasses the older USB 1.1 specification and adds a high speed rate. USB 2.0 now contains three speeds, Low, Full, and High. The Full Speed data rate is specified at 12.0 MBits/sec. Low Speed is1.5 MBits/sec and High Speed is 640 MBits/sec.
●The balance of this article will address the Full Speed specification only. The Full Speed rating is more than adequate for most handheld appliances. The reader may not understand why a device like a USB port needs signal switching at all; normally USB is expanded via active port expanders (hub). The value lies in the ability to reduce the number of pins that go to the outside world. For example, a digital camera almost assuredly needs a USB interface and the ability to deliver or receive other signals as well; video, audio, RS−232, charging, etc. The ability to reduce the number of pins going to the outside world, reduces the connector size, saves cost and improves reliability. In almost all cases, the equipment manufacturer supplies the required cables. For example, a connector may be Series A with a subminiature Series B connector on the other end. Another cable would be used for other purposes, for example, charging, video, RS−232, audio etc. The designer may use the 5.0 V power available from the USB cable to supply the switch. Using the available 5.0 V supply saves precious battery charge whenever the USB cable is connected. The data lines D+ and D− must be capable of being shorted to the power pin (5.0 V) for 24 hours, without harm to the equipment. This would present a problem to most analog switch designs, however the use of a low Vf Schottky diode prevents the switch from shorting to the lower voltage battery. When used for other than USB, it is assumed that the device is powered from its battery or from an external power source, in this case there are no mismatched voltage concerns.
●The USB Full Speed is a differential signal that varies between 0.8 V and 2.8 V, driving a 90Ω balanced cable. The series resistance is approximately 3.5Ω and each section is extremely well matched, so as not to introduce a common mode component. The small series resistance poses no problems to the USB signal, and the f3dB is well above the12 MBits/sec requirements. The threshold of the control signal on the NLAS4717 is adjusted lower than normal, so that when operating at 5.0 V (as in the case of USB) it can interface with almost any controller.

Brand of Product：	ON Semiconductor
Part#：	NLAS4717 、 NUP2301 More Part#
Product Category：	Analog Switch 、 low resistance analog switch More
Application：	More
Data Type：	Application note & Design Guide More
Safety & Environment Standards：	More
Operating Temperature：	Please see the document for details
Qualification Grade：	More
Qualification Approval：	More
Package：	TSSOP−6
Language：	English Chinese Chinese and English Japanese
Date of Creation：	May, 2004
Version Number：	Rev. 0
Data Encoding：	AND8158/D
Data Size：	98 KB

Data section preview(2pages)

- The full preview is over. If you want to read the whole 5 page document,please Sign in/Register -

Download

+1 Like
Add to Favorites

Recommend

Technical Resources

More>

All reproduced articles on this site are for the purpose of conveying more information and clearly indicate the source. If media or individuals who do not want to be reproduced can contact us, which will be deleted.

Integrated Circuits