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www.siliconstandard.com 1 of 5 SS7646 8/21/2004 rev.2.01 touch screen controller features description pin compatible with ss7643 serial interface interface for 4-wire touch-screen embedded touch-screen drivers internal 2.5v reference direct battery measurement (0v to 6v) touch-pressure measurement one auxiliary analog input on-chip temperature sensor supply voltage from 2.2v to 5.5v 12-bit analog-to-digital converter programmable 8- or 12-bit resolution conversion rate up to 125khz full power-down control 16 pin ssop package applications touch-screen monitors personal digital assistants point-of-sale terminals pagers high-speed data acquisition portable instruments low-power instruments the SS7646 touch-screen controller ic is an advanced version of the previous controller, the ss7643. the SS7646 is a 12-biit sar analog-to-digital converter (adc) with spi serial interface and low-on resistance drivers for 4-wire resistive touch screens. the SS7646 is fully pin-compatible with the ss7643. the SS7646 is a highly-integrated controller for portable applications using 4-wire resistive touch screens, such as pdas, portable instruments, cell phones, etc. the SS7646 contains all the analog and digital circuitry necessary to complete a pen request, and features temperature, battery monitor and touch-pressure measurements. the SS7646 also features an internal 2.5v reference that can be turned on or off independently of the adc. the SS7646 consumes only 405 w (with the internal reference off) at a sample rate of 125khz with a 2.7v supply and consumes less than 2.7 w in the shutdown mode. the SS7646 will operate with a supply down to 2.2v. the SS7646 is supplied in a very small 16-lead ssop package and is guaranteed over the temperature range. ordering information pin configuration ss76 46 15 /cs 16 dclk 14 din 12 dout 13 busy 11 /penirq 10 2 x+ 1 v dd 3 y+ 5 y- 4 x- 6 gnd 7 ssop-16 8 9 v ref v dd v bat v in SS7646tr SS7646 in ssop-16 shipped on tape and reel
www.siliconstandard.com 2 of 5 ss 7 6 4 6 8/21/2004 rev.2.01 absolute maximum ratings pin descriptions v dd to gnd???????????.??...???. -0.3v to +6v analog input to gnd??????????... -0.3v to v dd +0.3v digital input to gnd?????????...? -0.3v to v dd +0.3v operating temperature range???.??? -40 c to +85c maximum junction temperature???.??????? +150c storage temperature range??????.?..? -60c to +150 c lead temperature (soldering, 10s)??????..??? +300c caution: stresses above those listed in ?absolute maximum ratings? may cause permanent damage to the device. this is a stress only rating and operation of the device at these or any other conditions above those indicated in the operational sections of this specification is not implied. electrostatic discharge sensitivity this device can be damaged by esd. silicon standard recommends that all integrated circuits be handled with appropriate precautions. failure to observe proper handling and installation procedures can cause damage. esd damage can range from subtle performance degradation to complete device failure. pin name descr iption 1 v dd power supply, 2.2v to 5.5v. 2 x+ x+ input; adc input channel 1. 3 y+ y+ input; adc input channel 2. 4 x- x - input. 5 y- y- input; adc input channel 3. 6 gnd ground. 7 v bat ba ttery monit or input; adc input channel 4. 8 v in au xiliary input; adc input channel 5. 9 v ref reference voltage input / output. 10 v dd po w er supply, 2.2v to 5.5v. 11 /penirq pen interrupt. requires 10kw to 100kw external pull -up resistor. 12 dout serial data output. this output pin is high impedance when /cs is high. 13 busy busy output. this output pin is high impedance when /cs is high. 14 din serial data input. 15 /cs chip select input. this input is active low. 16 dclk external clock input. block diagram /cs dclk din dout busy /penirq y- v ref 6-channel mux x+ y+ x- v bat v in vdd charge redistribution dac comp sar control logic serial interface battery monitor temperature sensor internal 2.5v reference f i gu r e 1. bl o ck dia g ram o f ss 7646
www.siliconstandard.com 3 of 5 ss 7 6 4 6 8/21/2004 rev.2.01 electrical specifications (t a = -40 c to +85 c, v dd =+2.7v, v ref =+2.7v, f sample =125khz, f clk =24 * f sample , 12-bit mode, digital inputs= gnd or +v dd. typical values are at t a = +25 c, unless otherwise noted.) parameter test condit ions min. typ. max. units power supply requirement v dd quiescent current power dissipation specified performance functional operating range internal reference off internal reference on shut down mode internal reference off internal reference on shut down mode 2.7 2.2 150 600 0.40 1.62 3.6 5.5 1 2.7 v v a a a mw mw w system performance resolution inl dnl gain error offset error 12 2 1 4 6 bits lsb lsb lsb lsb digital input/output logic family v oh v ol v ih v il /penirq v ol cmos logic 100kw pull-up v dd * 0.8 v dd * 0.7 -0.3 0. 6 0.4 v dd + 0.3 0.8 v v v v v analog input input span input range capacitance 0 -0.2 25 v ref v dd + 0.2 v v pf reference output internal reference voltage internal reference thermal drift quiescent current internal reference on (pd1=?1?) (functional from 2.7v to 5.5v v dd ) 2.45 2.50 15 500 2.55 v ppm/ c a reference input input range input current internal reference off (pd1=?0?) 1 15 v dd v a x / y switches x+, y+ x -, y - switc h on-resistance switc h on-resistance 5 5 w w battery monitor input voltage range accuracy internal reference 0.5 -3 6.0 +3 v % t emperature measurement operating temperature range resolution accuracy diffe rential method (temp1-temp0) single conversion (temp0) diffe rential method (temp1-temp0) single conversion (temp0) -40 1.5 0.3 2 3 +85 c c c c c
www.siliconstandard.com 4 of 5 ss 7 6 4 6 8/21/2004 rev.2.01 timing specifications: (t a = -40c to +85c, v dd R
www.siliconstandard.com 4 of 5 ss 7 6 4 6 8/21/2004 rev.2.01 functional description overview the SS7646 is a 12-bit switched-capacitor sar analog-to-digital converter (adc). the converter is fabricated using a 0.6m cmos process and packaged in the very small 16-pin ssop package. the typical operation of the SS7646 is sh own in figure 12. the SS7646 operates on a single supply ranging from +2.2v to +5.5v. the SS7646 features an internal 2.5v reference and an external clock. the reference voltage directly sets the input range of the converter . the internal 2.5v reference can be turned on or off independently of the adc. the SS7646 contains six channel inputs, a serial interface and low on-resistance switches for the touch screen (see block diagram). the input to the convert er is s electe d via the six-channel m ultiple x er as shown in figure 5. serial interface the typical operation of the SS7646 serial interface ( /cs, dclk, d in and dout) is shown i n figu r e 2. the SS7646 communicates with microprocessors or digital signal processo rs via a synchronous se rial interface. one complete conversion can be accom plished with th ree serial co mmunic atio ns f or a total 24 clock cycles on the dclk input. operation of 24-clocks the operation is i nitiated by a f alling signal o n chip select (/cs) input. after /cs falls, the SS7646 looks for a s tart bit on the d in input. the first eight clock cycles are used to provide the cont rol byte. a t the end of the operation the /cs pin should be brought high. bringin g /cs high after the conversion als o minimiz es supply cu rrent if dclk is left running. bit 7 bit 6 bit 5 bit 4 bit 3 bit 2 bit 1 bit 0 start a2 a1 a0 m ode1 m ode0 pd1 pd0 table i. control bits in the control byte bit name description 7 start start bit. 6, 5, 4 a2, a1, a0 input channel selec t bits. 3, 2 mode1, mode0 12-bit / 8-bit resolution and int. reference configuration bits 1, 0 pd1, pd0 power down control bits table ii. descript ion of the control bits /cs dclk x/y swi tch din busy dout 18 1 18 sta rt a2 a1 a0 mode0 mode1 pd1 pd0 on conversion acquire tri-state tri-state tri-state tri-state 11 (msb) (lsb) 0 8 1 figure 2. serial interface of ss 7646
www.siliconstandard.com 4 of 5 ss 7 6 4 6 8/21/2004 rev.2.01 the control byte : table i and table ii show detailed information of the control byte (on din). the control byte provides the start operation, addressing, resolution, reference and power down information to the SS7646. start bit ? initiate start the control byte s tarts with the first high bit on din. the first bit must always be high (1) to initiate the start of the conversion. the SS7646 will ignore any inputs on the din until the start bit is detected. addressing bit s ? input channel selection the next three bits on control byte (a2, a1, a0) select the active input channel of the input m ultiplex er (se e table iii, and figure 5), and touch screen drivers. mode bits ? resolution and reference configuration the mode bits (mode1, mode0) set the resolution of the analog-to-digital (adc) converter. with the mode1 bit low (0) the following conversion will have 12 bits of resolution. with the mode1 bit high (1) t he followi ng conversion will have 8 bits of resolution. the mode0 bit set the reference input of the adc (see reference input section and figure 5). table iv shows detailed information of the mode bits. pd0 and pd1 bits - power down control the las t two bits (pd1, pd0) contr ol the power-d own mode and pen interrupt request of the SS7646. if both bits are high (1), the adc is always powered up and pen interrupt will be disabled. if both bits are low (0), the adc enters a power-down mode between conversions. the internal 2.5v voltage reference can be turned on or off independently of the adc with the pd1 bit. see table v for more information. a2 a1 a0 measure input channel x switch y switch 0 0 1 y-position x+ off on 1 0 1 x-position y+ on off 0 1 1 z1-position x+ x- on y+ on 1 0 0 z2-position y- x- on y+ on 0 1 0 battery v bat off off 1 1 0 auxiliary v in off off 0 0 0 temp0 - off off 1 1 1 temp1 - off off table iii. input channel configuration operation of 16-clocks the typic al operation of the SS7646 is 24-clocks (three control bytes) per conversion. however the cont rol bits for the next conversion can be overlapped with current conversion for a faster conversion. figure 3 shows the timing of 16-clocks per conversion. operation of 15-clocks the fastest operation (15-clocks per conversion) of SS7646 is shown on figure 4. this operation will not work with the serial interface of most microcontrollers and digital signal processors, as they are not capable of providing 15 clocks cycles per serial transfe r . mode1 mode0 resolution a dc reference 0 1 12bits v ref 0 0 12bits v dd * 1 1 8bits v ref 1 0 8bits v dd * table iv. resolution and reference configuration * when measuring y (001), x (101), z1(011) and z2(100) positions, otherwise invalid configuration pd1 pd0 /penirq description 0 0 enable the re fe rence is switc hing off and the adc will power down between conversions. y- switch is on while in power-down. 0 1 enable the re fe rence is switc hing off and the adc is on permanently. no power down between conversions. 1 0 enable the reference is on and the adc will power down between conversions. 1 1 disable the reference and the adc are on. no power down between conversions, the adc always power up. the pen interrupt functionality will be disabled. table v. power-down and pen interrupt selection
www.siliconstandard.com 4 of 5 ss 7 6 4 6 8/21/2004 rev.2.01 /cs dclk x/y switch din busy dout on 1 81 1 8 1 on (msb) (lsb) 11 11 10 9 (msb) 0 8 16 1 f i gu r e 3. t imi n g o f 16 - cl o cks p er c o n v ersi o n /cs dclk x/y switch din busy dout on 181 18 1 on (msb) (lsb) 11 11 10 9 (msb) 0 7 15 1 1 f i gu r e 4. t imi n g o f 15 - cl o cks p er c o n v ersi o n
www.siliconstandard.com 4 of 5 ss 7 6 4 6 8/21/2004 rev.2.01 a2a1a0 (shown 101) y- x+ y+ x- v bat v in vdd battery monitor /penirq adc +ref -ref in v ref mode0 (shown 1) v dd figu r e 5 . di a g r a m of input ch a nn e l a nd r e f e r e n c e input analog input measurement t he SS7646 contains 6 channel inputs. x+, y+ and y - in p uts a r e f or tou c h screen m ea s u r e m ent, 2 au x i l ia r y inputs are v bat and v in . the diode input (internal node) is for temperature measurement. figure 5 shows a diagram of the analog input channel and reference input. the input to the a/d converter is selected via the six-channel m ultiplexer. (see block diagram and figure 5.) input channel table iii shown the input channel configuration of the ss 7646. the control bits are set via the din pin. (see control byte section). the selected channel is for a/d converter input. please refer to figure 5 for detailed input channel multiplexer. for measuring x+ (y-position) and y+ (x-p osition), y switches and x switches are turned on respectively. internal reference t he SS7646 has an internal 2.5v voltage reference that can be turned on with the power-down address bit, pd1=?1?, at the configuration byte (see table v and figure 1). the internal re fe rence volta ge of SS7646 should be turned off (pd1=?0?) in o rder to be compatible with the ss7643. if the internal reference is turned off and the reference is taken f r om the p o wer s u pp l y d i r e c t l y , s pe c i a l c a r e m u s t be ta k en t o a v o i d n oi s e f r om the p o w er s u p p l y . while the adc can be powered up or down instantly, the internal reference requires settling time to settle to the final value. the power-up time of v ref is typically 30 s without a load. the internal reference voltage c an be tu r n e d o n or o f f i nde p en d en t l y of the adc . t his a l l o w s e x t r a t i m e f o r the r e f e r en c e v o lt a ge t o be s e t t l e d be f o r e a c o n v e r s i on. although / c s = ? 1? wi l l put the ss 7646 into a power-down mode i m m ediate l y , the inte r nal r e f e r en c e does not turn o f f wi t h / c s g o ing h i g h . a n a d d i t i on a l pattern with pd1=? 0? is require d before /cs goes high.
www.siliconstandard.com 4 of 5 ss 7 6 4 6 8/21/2004 rev.2.01 reference input the voltage diffe rence be tween +ref and ?ref (shown v ref in figure 5), in the range of 1v to + v dd, sets the analog-to-digital converter (adc) input range. t he full-scale a nalog input range of the SS7646 is therefore from 0 to v ref . t y pi c a l l y the r e f e r en c e i np u t is an e x te r nal p r e c i s e voltage sourc e v ref (m ode0=1, see table iv) for tou c h screen and au x iliary inputs m e a s u r e m e n t. figure 6 shows the configuration for a y coordinate measurement with mode0=1. when utilizing the panel measurement, the v ref must equal v dd as input range is from 0 to v dd . if the reference input is from the po w er s upp l y di r e c t l y , as f i gu r e 12 s ho w s f or example, special ca r e m ust be taken to avoid n oise f r om the po w er s uppl y . w h en m a k i ng tou c h screen m ea s u r e m ents on l y , t h e reference input can be set from v dd directly ( m o d e0= 0 ) and discard the v ref input. figure 7 shows the configuration for a y coordinate measurement with mode0=0. examples of din configuration table vi shows din configurations for specified applications. adc v ref a2a1a0 (shown 101) +ref -ref mode0 = 1 in x+ v dd gnd y- y+ v dd gnd internal 2.5v reference figu r e 6 . t o u ch screen m eas u reme n t w i t h m o de0=1 adc v ref a2a1a0 (shown 101) +ref -ref mode0 = 0 in x+ v dd gnd y- y+ v dd gnd internal 2.5v reference figu r e 7 . t o u ch screen m eas u reme n t w i t h m o de0=0 measurement s a2 a1 a0 mode1 mode0 pd1 pd0 +ref x switches y switches touch screen y-position (x+) 1 0 0 1 0 0 / 1 0 0 v dd / v ref off on x-position (y+) 1 1 0 1 0 0 / 1 0 0 v dd / v ref on off z1-position (x+) 1 0 1 1 0 0 / 1 0 0 v dd / v ref x+ off, x- on y+ on , y- off z2-position (y -) 1 1 0 0 0 0 / 1 0 0 v dd / v ref x+ off, x- on y+ on , y- off battery v bat 1 0 1 0 0 1 1 1 v ref off off - 1 0 1 0 * 0 * * invalid configuration auxiliary in. v in 1 1 1 0 0 1 1 1 v ref off off - 1 1 1 0 * 0 * * invalid configuration temperature temp1 1 1 1 1 0 1 1 1 v ref off off temp0 1 0 0 0 0 1 1 1 v ref off off - 1 1 1 1 * 0 * * invalid configuration - 1 0 0 0 * 0 * * invalid configuration t a b l e v i . e xa mpl e s of din configu r a t ion
www.siliconstandard.com 4 of 5 ss 7 6 4 6 8/21/2004 rev.2.01 temperature measurement the temperature measurement is based on an on-chip forward diode measurement. the forward diode voltage v be has a well - de f ine d c ha r a c te r i s t ic vs . te m pe r atu r e. t he r e a r e t w o m ea s u r e m ent op t i o ns for the SS7646, a single conversion mode and a differential conversion mode. (1) in the single conversion mode, a diode voltage is first digitized at a fixed calibration temperature (25 c ) during the final te st of the end product and this value t 1 is stored i n the memo ry, the n only a sing l e re ad ing t2 is required for the users to obtain the ambient temperature through extrapolation from the calibration temperature diode result. this result assumes a diode temperature coefficient (tc) of approximately ? 2.1 mv/ c. this method provides a resolution of approximately 0.3 c and a predicted accuracy of d 3 c. t his mode is achieved with an address s etting of a2=0, a1=0, a0=0 (temp0). please ref er to table iii and figure 8 for details. (2) the differential conversion mode requires two points measurement to eliminate the need for absolute temperature calibration. the first measurement temp0 (a2=0, a1=0, a0=0) is performed with a fixed bias current into a diode and the second measurement temp1 (a2=1, a1 =1 , a0=1) is pe rformed with n tim es (n=120 for SS7646) of the bias current into the same diode. the voltage difference between first and second readings is proportional to absolute temperature and is given by the f ollowing fo rmula: where v be represents the diode voltage, n is the bias current m ultipl e, k is boltzmann?s constant and q is the electron charge. taking boltzmann?s constant k=1.38054x10 -23 electrons volts/degrees kelvin, the electron charge q=1.602189x10 -19 coulomb, then the ambient te m pe r atu r e t , in d eg r ee s c en t ig r ad e , w o u l d b e c alculated as f ollows: t h is m e thod p r o v i d es a m u c h i m p r ov e d a b s o l u t e m ea s u r e m ent of temperature of d 2 c, h o we v e r re solution is redu ced to approximately 1.5 c/lsb. /penirq vdd adc mux 6 channel x+ on off off in * i figu r e 8 . bl o ck dia g ram o f t em p era t u r e m eas u reme n t circ u it adc dc/dc converter a2a1a0 (shown 010) battery 0v to 6v v bat v dd on on 7.5k 2.5k figu r e 9 . bl o ck dia g ram o f ba tt ery measurement circuit ln(n) x )qkt( ?
www.siliconstandard.com 4 of 5 ss 7 6 4 6 8/21/2004 rev.2.01 battery measurement another feature of the SS7646 is the battery measurement ability. figure 9 shows a block diagram of a battery voltage monitored by the SS7646. while the main power to the SS7646 via the dc/dc regulator is maintained at the desired voltage, the battery voltage can vary from 0.5v to 6v. the SS7646 is able to monitor this battery voltage thro ugh the v bat pin. the voltage on v bat pin is divided down by 4 so that the battery voltage of 6v becomes 1.5v to the adc input. in order to minimize the power consumption, the divider is only on during the sampling phase of the adc. see table v for the control bit configurations required to perform this battery measurement. pressure measurement the SS7646 is also able to determine the pen or finger touch through the pressure measurement with some simple calculations. the pressure measurement is based on the contact resistance between the x and y plates. figure 10 shows a block diagram of the pressure measurement. there are two r e c o m m ended m ethods to pe r f or m the m ea s u r e m ent. generally, the pressure measurement can be accomplished sufficiently with 8-bit resolution mode, but the fo llowing examples are sh own with the 12-bit resolution mode. y+ y- x+ x- rtouch y+ y- x+ x- rtouch measure x-position measure z1-position y+ y- x+ x- rtouch measure z2-position v v v figure 10. b lock d iag r am of p r essu r e measu r ement (1) the first method requires the user knowing the x-plate resistance. performing thr ee touch screen conversions, x-posi ti on, z1-position and z2-position, then use the following equation to calculate the touch re sistance: (2) the second method requires the user knowing both the x-plate and y-plate resistance. performing three touch screen conversions, x-position, y-position and z1-position, then use the following equation to calculate the touch resistance: pen interrupt request the pen interrupt function is shown in figure 11. normally the /penirq is high by connecting a pull-up resi stor (typical ly 100k ) to v dd . if /pe nirq has been enabled (see table v), y- driver is on and connected to gnd and /penirq diode is connected to x+ inp ut. when the touch screen connected to t he SS7646 is touched, the x+ input is pulled to ground through the touch screen and /penirq will go low, initiating an interrupt to the microprocessor. during the x and y plates measurement cycles, the /penirq diode will be internally connected to gnd and x+ input disconnected from the diode to eliminate leakage current to the touch screen. y+ y- x+ /penirq enable v dd 100k /penirq figure 11. block diagram of pen interrupt circuit 1) 12positionxplatetouch z(z x )4096(x x rr 4096)x yr( - z(4096x 4096)xx r(r position yplate 1position xplatetouch 1)
www.siliconstandard.com 4 of 5 ss 7 6 4 6 8/21/2004 rev.2.01 application considerations typical operating circuit SS7646 1 2 3 4 5 6 7 8 16 15 14 /cs dclk din dout busy /penirq v ref x+ v dd y+ y- x- 2.7v to 5.5v 13 12 11 10 9 gnd clock chip select data in busy status data out pen interrupt v dd v bat v in battery dc/dc converter figure 12. typical operation circuit of the SS7646 resistive touch screen (4-wire) the 4-wire resistive touch screen consists of 2 resistive plates that are separated by a small gap. each of the plates has a resistance in the range from 200 to 2000 ohms. the screen works by applying a voltage across the x plate or y plate resistive networks. if a voltage is applied, for example, between x+ and x- then a voltage divider is formed on the x plate. when the y plate is touched to the x plate, a voltage will be developed on the y plate. by accu ra te ly measuring this v oltage, the position on the screen can be determined. the connections between the SS7646 and the touch screen should be as short as possible. y+x-x+ y- x plate y plate electrode figure 13. 4-wire resistive touch screen
information furnished by silicon standard corporation is believed to be accurate and reliable. however, silicon standard corporation makes no guarantee or warranty, express or implied, as to the reliability, accuracy, timeliness or completeness of such information and assumes no responsibility for its use, or for infringement of any patent or other intellectual property rights of third parties that may result from its use. silicon standard reserves the right to make changes as it deems necessary to any products described herein for any reason, including without limitation enhancement in reliability, functionality or design. no license is granted, whether expressly or by implication, in relation to the use of any products described herein or to the use of any information provided herein, under any patent or other intellectual property rights of silicon standard corporation or any third parties. www.siliconstandard.com 5 of 5 ss 7 6 4 6 8/21/2004 rev.2.01 package information ssop-16 dimensions (mm) dimensions (mil) symbols min. nom. max. min. nom. max. a a 1 a 2 b c d e h e 0.6358 bsc 25 bsc l h e ee ec 8 1 9 16 e h b l e detail f h x 45c see detail f c d seating plane a 1 a 2 a t(4x) e 1.75 0.25 1.50 0.30 0.25 5.00 4.00 6.80 1.27 0.50 8 1.60 0.254 0.203 3.90 6.00 0.635 0.42 4.90 0.15 1.35 0.10 0.20 0.18 4.80 3.80 5.80 0.40 0.25 0 c 53 4 8 7 189 150 228 16 10 0 c 25 17 193 63 154 236 6 10 8 68 10 59 12 10 197 157 244 50 20 8 c

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