TI Touch Screen Controller Replaces Five Chips from Original iPhone

Posted by  23 February 2010

What does the Apple iPhone 3GS have in common with your regular ticketing kiosk? How about the Nintendo DS handheld game console and a regular bank teller machine? All of these products use touch screen technology solutions in one form or another, as provided by the leading controller suppliers for the last several years.

It has been generally accepted that the term refers to the ability to interact physically with what is shown on a display, via touch or contact, using either a finger, hand, or pen. The popularity of this application is mainly due to its ease of use, as well as the intuitive interfaces enabled by its use. With a market forecasted to grow to $9 billion dollars by 2015 (from $3.6 billion in 2008), there has been a flurry of activity in this sector, with some analysts reporting over 170 suppliers in the supply chain today.

The most popular technology used in touch screens is the resistive 4-wire and 5-wire approach, due to low cost and simple interface electronics. There is also a recent notable increase in overall shipping of products based on the Projected Capacitive Touch or PCT approach. This technology is used by Apple, for its iPhone and iPod Touch, and others including the Samsung Pixon12 and Sony Ericsson Satio.

Looking closer at the perennial (can I say that?) media favorite, the Apple iPhone, touch screen development has undergone a radical change from the 2G all the way to the 3GS model. Back in the 2G era, the touch screen controller function was implemented using a number of ICs mounted on a single mini PCB. The ICs include Apple’s custom sensing IC (fabricated by Broadcom with die markings BCM5973A), a Texas Instruments (TI) driving IC (CD3238), an NXP MCU (LPC2221 – 32 bit ARM Core), a Hosonic crystal, and an ATMEL EEPROM.

IM-1-2g-ts-back      IM-2-2g-ts-front


Figure 1  Front and Back of Touch Screen Board from the iPhone 2G

The second generation 3G did not have the miniPCB. Instead, the Sensing IC, MCU, EEPROM, and crystal were all incorporated into Broadcom’s BCM5974 touch screen controller IC, while TI’s CD3239 replaced the CD3238.

The latest iPhone 3GS model appears to have integrated all five of the 2G’s touch screen controller functions under a single custom IC, with package markings 343S0464. The die markings F761586C indicate that winning this high volume socket, and also the related iPod Touch and Magic Mouse sockets, is a coup for Texas Instruments. Getting the required functionality onto a single chip was facilitated by fabricating at 90 nm. In fact, TI has been gaining some other big socket wins in this industry, notably the Motorola DROID resistive touch screen (using TI’s TSC2046 4-wire touch screen controller with low voltage digital I/O).


Figure 2  iPhone 3GS Board Showing Single Chip for Touch Screen Control

Figure 3  Die Photograph of TI Touch Screen Controller Delayered to Bottom Metal Layer

What is most impressive is that each of these wins shows TI’s breadth of technology to serve this market. In the case of the iPhone, TI has delivered a chip that is over 50% digital and memory. In the Droid, TI won with a tried and true design that is almost entirely analog circuitry, and appears to be the same as the touch screen technology from TI's acquisition Burr-Brown that Chipworks analyzed 10 years ago; though we haven’t extracted any circuitry on today’s chip, you can see the layout is very similar.

IM-5-burr-brown-die1   IM-6-ti-motorolla1     

Figure 4  Comparison of Burr-Brown ADS7846 and TI TSC2046 Touch Screen Controllers
Of course, now we have Apple's latest product launch, the question will be who wins the controller socket in the iPad?  This is a hot and heavy sector these days, and with new entrants like Synaptics getting the design win in the Google Nexus One, nothing can be taken for granted.

Last modified on Tuesday, 20 April 2010 22:28