A8946

A8946 AITSEMI | Alldatasheet

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AiT Semiconductor Inc. www.ait-ic.com A8946 TOUCH SCREEN DRIVER 4-WIRE RESISTANCE, LOW-VOL TAGE I/O INTERFACE REV1.3 - DEC 2007 RELEASED, JAN 2014 UPDATED - - 1 - DESCRIPTION FEATURES The A8946 is a 4 -wire touch screen driver which supports a low -voltage I/O interface from 1.5V to 5.25V. The A8946 has an on -chip 2.5V reference that can be used for the auxiliary input, battery monitor, and temperature measurement modes. The reference can also be powered down when not used to conserve power. The internal reference operates down to 2.7V suppl y voltage, while monitoring the battery voltage from 0V to 6V. The A8946 is a highly integrated driver for portable applications with 4 -wire resistive touch panel such as, PDA, portable instruments, cellular phone, etc. The A8946 is available in QFN16 package.

ORDERING INFORMATION

V: Halogen free Package R: Tape & Reel AiT provides all RoHS products Suffix “ V “ means Halogen free Package  1.5V to 5.25V digital I/O  2.2V to 5.25V operation  4-wire I/F  Internal 2.5V reference  Direct battery measurement(0V to 6V)  Programmable 8 or 12 bit Resolution  Temperature measurement  Touch-pressure measurement  Available in QFN16 Package. APPLICATION  Cellular Phones  Personal Digital Assistants  Portable Instruments  Touch Screen Monitors  Screen Signature Board  Digital Still Camera TYPICAL APPLICATION

AiT Semiconductor Inc. www.ait-ic.com A8946 TOUCH SCREEN DRIVER 4-WIRE RESISTANCE, LOW-VOL TAGE I/O INTERFACE REV1.3 - DEC 2007 RELEASED, JAN 2014 UPDATED - - 2 - PIN DESCRIPTION Top View Pin # Symbol Functions 1 BUSY Busy Output. This output is high impedance when CS is high.

2 DIN

Serial Data Input. If CS is low, data is latched on rising edge of DCLK. CS Chip Select Input. Controls conversion timing and enables the serial input/output register. CS high = power -down mode (ADC only). 4 DCLK External Clock Input. This clock runs the SAR conversion process and synchronizes serial data I/O. 5 +VCC Power Supply

6 X+ X+ Position Input

7 Y+ Y+ Position Input

8 X- X– Position Input

9 Y- Y– Position Input

10 GND Ground

11 VBAT Battery Monitor Input

12 AUX Auxiliary Input to ADC

13 VREF Voltage Reference Input / Output

14 IOVDD Digital I/O Power Supply

15 PENIRQ Pen Interrupt

16 DOUT

Serial Data Output. Data is shifted on the falling edge of DCLK. This output is high impedance when CS is high.

AiT Semiconductor Inc. www.ait-ic.com A8946 TOUCH SCREEN DRIVER 4-WIRE RESISTANCE, LOW-VOL TAGE I/O INTERFACE REV1.3 - DEC 2007 RELEASED, JAN 2014 UPDATED - - 3 - ABSOLUTE MAXIMUM RATINGS +VCC and IOVDD to GND -0.3V to +6V Analog Inputs to GND -0.3V to +VCC+0.3V Digital Inputs to GND -0.3V to IOVDD +0.3V Lead Temperature (soldering, 10s) +300°C Maximum Junction Temperature +150°C Operating Temperature Range -40°C to +85 °C Power Dissipation 250mW Storage Temperature Range -65°C to + 150°C

AiT Semiconductor Inc. www.ait-ic.com A8946 TOUCH SCREEN DRIVER 4-WIRE RESISTANCE, LOW-VOL TAGE I/O INTERFACE REV1.3 - DEC 2007 RELEASED, JAN 2014 UPDATED - - 4 - ELECTRIC CHARACTERISTICS TA = –40°C to +85°C, +VCC = +2.7V, VREF = 2.5V Internal Voltage, FSAMPLE = 125 KHz, FCLK = 16 * FSAMPLE = 12 MHz, 12-bit Mode, Digital Inputs = GND or IOVDD, and +VCC must be * IOVDD, Symbol Parameter Conditions Min Typ. Max Unit Reference Output Internal Reference Voltage 2.46 2.50 2.54 V Internal Reference Drift 15 ppm/℃ Quiescent Current 500 uA Analog Input Full-Scale Input Span Positive Input - Negative Input 0 VREF V Absolute Input Range Positive Input -0.2 +VCC+0.2 V Negative Input -0.2 +0.2 V Capacitance 25 pF Leakage Current 0.1 uA Temperature Measurement Temperature Range -40 +85 °C Resolution Differential MethodNOTE3 1.6 °C TEMPONOTE4 0.3 °C Accuracy Differential MethodNOTE3 ±2 °C TEMPONOTE4 ±3 °C System Performance Resolution 12 Bits No Missing Codes 11 Bits Integral Linearity Error ±2 LSBNOTE1 Offset Error ±4 LSB Gain Error External VREF ±6 LSB Noise Including Internal VREF 70 uVRMS Power-Supply Rejection 70 dB Sampling Dynamics Conversion Time 12 CLK Cycles Acquisition Time 3 CLK Cycles Throughput Rate 125 KHz Multiplexer Settling Time 500 ns Aperture Delay 30 ns Aperture Jitter 100 ps Channel-to-Channel Isolation VIN = 2.5Vp-p at 50KHz 100 dB Battery Monitor Input Voltage Range 0.5 6 V Input Impedance Sampling Battery 10 KΩ Battery Monitor Off 1 GΩ Accuracy VBAT = 0.5V to 5.5V, External VREF =2.5V -2 +2 % VBAT = 0.5V to 5.5V, Internal Reference -3 +3 %

AiT Semiconductor Inc. www.ait-ic.com A8946 TOUCH SCREEN DRIVER 4-WIRE RESISTANCE, LOW-VOL TAGE I/O INTERFACE REV1.3 - DEC 2007 RELEASED, JAN 2014 UPDATED - - 5 - NOTE1. LSB means least significant bit. With VREF = +2.5V, one LSB is 610μV. NOTE2. Assured by design, but not tested. Exceeding 50mA source current may result in device degradation. NOTE3. Difference between TEMP 0 and TEMP 1 measurement no calibration necessary. NOTE4. Temperature drift is –2.1mV/°C. NOTE5. A8946 operates down to 2.2V. NOTE6. IOVDD must be - +VCC. NOTE7. Combined supply current from +VCC and IOVDD. Typical values obtained from conversions on AUX input with PD0 = 0. Symbol Parameter Conditions Min Typ Max Unit Reference Input Range 1.0 +VCC V Input Impedance SER/ = D, PD1=0, Internal Reference Off 1 GΩ Internal Reference On 250 Ω Digital Input / Output Logic Family CMOS VIH I | IH | ≦+5uA IOVDD*0.7 IOVDD+0.3 V VIL I | IL | ≦+5uA -0.3 0.3*IOVDD V VOH LOH = -250uA IOVDD*0.8 V VOL LOL = 250uA 0.4 V Data Format Straight Binary Power-Supply Requirements +VCCNOTE5 Specified Performance 2.7 3.6 V Operating Range 2.2 5.25 V IOVDONOTE6 1.5 +VCC V Quiescent CurrentNOTE7 Internal Reference Off 280 650 uA Internal Reference On 780 uA FSAMPLE= 12.5KHz 220 uA Power-Down Mode with CS =DCLK=DIN=IOVDD 3 uA Power Dissipation +VCC=+2.7V 1.8 mW Temperature Range Specified Performance -40 +85 °C Switch Drivers Qn-Resistance Y+，X+ 5 Ω Y-，X- 6 Ω Drive CurrentNOTE2 Duration 100ms 50 mA

AiT Semiconductor Inc. www.ait-ic.com A8946 TOUCH SCREEN DRIVER 4-WIRE RESISTANCE, LOW-VOL TAGE I/O INTERFACE REV1.3 - DEC 2007 RELEASED, JAN 2014 UPDATED - - 6 - DETAILED INFORMATION See Fig. 1 to Fig. 12 show application schematics for differential and single-ended inputs. Fig. 1 Typical Differential Input Application ANALOG INPUT Table 1 and Table 2 show the relationship between the A2, A1, A0, and SER/ control bits and the configuration of the A8946. The control bits are provided serially via the DIN pin (see the Digital Interface section of this data sheet for more details). When the converter enters the hold mode, the voltage difference between the +IN and –IN inputs is captured on the internal capacitor array. The input current into the analog inputs depends on the conversion rate of the device. During the sample period, the source must charge the internal sampling capacitor. After the capacitor has been fully charged, there is no further input current. The rate of charge transfer from the analog source to the converter is a function of conversion rate. Table 1 Input Configuration (DIN), Single-Ended Reference Mode (SER/ High).

AiT Semiconductor Inc. www.ait-ic.com A8946 TOUCH SCREEN DRIVER 4-WIRE RESISTANCE, LOW-VOL TAGE I/O INTERFACE REV1.3 - DEC 2007 RELEASED, JAN 2014 UPDATED - - 7 - Table 2 Input configuration (DIN), Differential Reference Mode (SER/ Low) Internal reference The A8946 has an internal 2.5V voltage reference that can be turned on or off with the control bit, PD1 (see Table 5). Typically, the internal reference voltage is only used in the single-ended mode for battery monitoring, temperature measurement, and for using the auxiliary input. Optimal touch screen performance is achieved when using the differential mode. Reference Input The voltage difference between +REF and –REF sets the analog input range. The A8946 operates with a reference in the range of 1V to +V CC. There are several critical items concerning the reference input and its wide voltage range. As the reference voltage is reduced, the analog voltage weight of each digital output code is also reduced. This is often referred to as the LSB size and is equal to the reference voltage divided by 4096 in 12-bit mode. Any offset or gain error inherent in the AD C appears to increase, in terms of LSB size, as the reference voltage is reduced. With a lower reference voltage, more care must be taken to provide a clean layout including adequate bypassing, a clean power supply, a low -noise reference, and a low -noise i nput signal. The voltage into the V REF input directly drives the capacitor digital -to-analog converter (CDAC) portion of the A8946. Therefore, the input current is very low. There is also a critical item regarding the reference when making measurements whi le the switch drivers are ON. For this discussion, it is useful to consider the typical application of the A8946. This particular application shows the device being used to digitize a resistive touch screen. A measurement of the current Y -Position of the pointing device is made by connecting the X+ input to the ADC, turning on the Y+ and Y – drivers, and digitizing the voltage on X+. For this measurement, the resistance in the X+ lead does not affect the conversion. However, since the resistance between Y+ and Y– is fairly low, the on-resistance of the Y drivers does make a small difference. Under the situation outlined so far, it is not possible to achieve a 0V input or a full-scale input regardless of where the pointing device is on the touch screen because some voltage is lost across the internal switches. In addition, the internal switch resistance is unlikely to track the resistance of the touch screen, providing an additional source of error.

AiT Semiconductor Inc. www.ait-ic.com A8946 TOUCH SCREEN DRIVER 4-WIRE RESISTANCE, LOW-VOL TAGE I/O INTERFACE REV1.3 - DEC 2007 RELEASED, JAN 2014 UPDATED - - 8 - Fig. 2 Diagram of Single-Ended Reference (SER/DFR High, Y switches enabled, X+ is analog input) This situation can be remedied (see Fig 3). By setting the SER/ bit low, the +REF and –REF inputs are connected directly to Y+ and Y –, respectively, which makes the analog -to-digital conversion ratio metric. The result of the conversion is always a percentage of the external resistance, regardless of how it changes in relation to the on -resistance of the internal switches. Note that there is an important consideration regarding power dissipation when using the ratio metric mode of operation. As a final note about the differential reference mode, it must be used with +V CC as the source of the +REF voltage and cannot be used with V REF. It is possible to use a high -precision reference on V REF and single-ended reference mode for measurements which do not need to be ratio metric. In some cases, it is possible to power the converter directly from a precision reference. Most references can provide enough power for the A8946, but might not be able to supply enough current for the external load (such as a resistive touch screen).

AiT Semiconductor Inc. www.ait-ic.com A8946 TOUCH SCREEN DRIVER 4-WIRE RESISTANCE, LOW-VOL TAGE I/O INTERFACE REV1.3 - DEC 2007 RELEASED, JAN 2014 UPDATED - - 9 - Fig. 3 Diagram of Differential Reference (SER/DFR Low, Y switches enabled, X+ is analog input) Touch Screen Setting In some applications, external capacitors may be required across the touch screen for filtering noise picked up by the touch screen. These capacitors provide a low-pass filter to reduce the noise, but because a settling time requirement when the panel is touched that typically show up as a gain error. There are several methods for minimizing or eliminating this issue. The problem is the input and/or reference has not settled to the final steady-state value prior to the ADC sampling the input(s) and providin g the digital output. Additionally, the reference voltage may still be changing during the measurement cycle. Option 1 is to stop or slow down the A8946 DCLK for the required touch screen settling time. This allows the input and reference to have stable values for the Acquire period ( 3 clock cycles of the A8946; see Fig . 7). This works for both the single -ended and the differential modes. Option 2 is to operate the A8946 in the differential mode only for the touch screen measurements and command the A8946 to remain on (touch screen drivers ON) and not go into power-down (PD0 = 1). Several conversions are made depending on the settling time required and the A8946 data rate. Once the required number of conversions had been made, the processor commands the A894 6 to go into its power-down state on the last measurement. This process is required for X -Position, Y -Position, and Z-Position measurements. Option 3 is to operate in the 15 Clock -per-Conversion modes, which overlaps the analog-to-digital conversions and m aintains the touch screen drivers on until commanded to stop by the processor (see Fig. 11).

AiT Semiconductor Inc. www.ait-ic.com A8946 TOUCH SCREEN DRIVER 4-WIRE RESISTANCE, LOW-VOL TAGE I/O INTERFACE REV1.3 - DEC 2007 RELEASED, JAN 2014 UPDATED - - 10 - Temperature Measurement In some applications, such as battery recharging, a measurement of ambient temperature is required. The temperature measurement technique used in the A8946 relies on the characteristics of a semiconductor junction operating at a fixed current level. The forward diode voltage (V BE) has a well -defined characteristic versus temperature. The ambient temperature can be predicted in applications by knowing the +25°C value of the VBE voltage and then monitoring the delta of that voltage as the temperature changes. The A8946 offers two modes of operation. The first mode requires calibration at a known temperature, but only requires a single reading to predict the ambient temperature. A diode is used (turned on) during this measurement cycle. The voltage across the diode is connected through the MUX for digitizing the forward bias voltage by the ADC with an address of A2 = 0, A1 = 0, and A0 = 0 (see Table 1 and Fig 4 for details). This voltage is typically 600mV at +25°C with a 20μA current through the diode. The absolute value of this di ode voltage can vary a few mill volts. However, the TC of this voltage is very consistent at –2.1mV/°C. During the final test of the end product, the diode voltage would be stored at a known room temperature, in memory, for calibration purposes by the user. The result is an equivalent temperature measurement resolution of 0.3°C/LSB (in 12 -bit mode). Fig. 4 Functional Block Diagram of Temperature Measurement Mode

AiT Semiconductor Inc. www.ait-ic.com A8946 TOUCH SCREEN DRIVER 4-WIRE RESISTANCE, LOW-VOL TAGE I/O INTERFACE REV1.3 - DEC 2007 RELEASED, JAN 2014 UPDATED - - 11 - The second mode does not require a test temperature calibration, but uses a two -measurement method to eliminate the need for absolute temperature calibration and for achieving 2°C accuracy. This mode requires a second conversion with an address of A2 = 1, A1 = 1, and A0 = 1, with a 91 times larger current. The voltage difference between the first and second conversion using 91 times the bias current is represented by kT/q * ln (N), wher e N is the current ratio = 91, k = Boltzmann’s constant (1.38054 * 10 –23 electron volts/ degrees Kelvin), q = the electron charge (1.602189 * 10 –19 C), and T = the temperature in degrees Kelvin. This method can provide improved absolute temperature measurement over the first mode at the cost of less resolution (1.6°C/LSB). The equation for solving for °K is: °K = q * △V/(k • ln (N)) Where, V = V (I91) – V (I1) (in mV) NOTE: The bias current for each diode temperature measurement is only on for 3 clock cycles (during the acquisition mode) and, therefore, does not add any noticeable increase in power, especially if the temperature measurement only occurs occasionally. Battery Measurement An added feature of the A8946 is the ability to monitor the battery voltage on the othe r side of the voltage regulator (DC/DC converter), as shown in Fig . 5. The battery voltage can vary from 0V to 6V, while maintaining the voltage to the A8946 at 2.7V, 3.3V, etc. The input voltage (VBAT) is divided down by 4 so that a 5.5V battery voltage is represented as 1.375V to the ADC. This simplifies the multiplexer and control logic. In order to minimize the power consumption, the divider is only on during the sampling period when A2 = 0, A1 = 1, and A0 = 0 (see Table 1. for the relationship between the control bits and configuration of the A8946).

AiT Semiconductor Inc. www.ait-ic.com A8946 TOUCH SCREEN DRIVER 4-WIRE RESISTANCE, LOW-VOL TAGE I/O INTERFACE REV1.3 - DEC 2007 RELEASED, JAN 2014 UPDATED - - 12 - Fig. 5 Battery Measurement Functional Block Diagram Pressure Measurement Measuring touch pressure can also be done with the A8946. To determine pen or finger touch, the pressure of the touch needs to be determined. Generally, it is not necessary to have very high performance for this test, therefore, the 8-bit resolution mode is recommended (however, calculations will be shown here in the 12 -bit resolution mode). There are several different ways of pe rforming this measurement. The A8946 supports two methods. The first method requires knowing the X -plate resistance, measurement of the X -Position, and two additional cross panel measurements (Z 1 and Z2) of the touch screen, as shown in Fig . 6 using equation 2 calculates the touch resistance:

AiT Semiconductor Inc. www.ait-ic.com A8946 TOUCH SCREEN DRIVER 4-WIRE RESISTANCE, LOW-VOL TAGE I/O INTERFACE REV1.3 - DEC 2007 RELEASED, JAN 2014 UPDATED - - 13 - The second method requires knowing both the X-plate and Y-plate resistance, measurement of X-Position and Y-Position, and Z1. Using Equation 3 also calculates the touch resistance: Fig. 6 Pressure Measurement Block Diagrams

AiT Semiconductor Inc. www.ait-ic.com A8946 TOUCH SCREEN DRIVER 4-WIRE RESISTANCE, LOW-VOL TAGE I/O INTERFACE REV1.3 - DEC 2007 RELEASED, JAN 2014 UPDATED - - 14 - Digital Interface Fig. 7 shows the typical operation of the A8946 digital interface. This diagram assumes that the source of the digital signals is a microcontroller or digital signal processor with a basic serial interface. Each communication between the processor and the converter, such as SPI or SSI synchronous serial interface, consists of 8 clock cycles. One complete conversion can be accomplished with three serial communications for a total of 24 clock cycles on the DCLK input. The first 8 clock cycles are used to provide the control byte via the DIN pin. When the co nverter has enough information about the following conversion to set the input multiplexer and reference inputs appropriately, the converter enters the acquisition (sample) mode and, if needed, the touch panel drivers are turned on. After three more clock cycles, the control bytes is complete and the converter enters the conversion mode. At this point, the input sample -and-hold goes into the hold mode and the touch panel drivers turn off (in the single-ended mode). The next 12 clock cycles accomplish the actual analog -to-digital conversion. If the conversion is ratio metric (SER/ = 0), the drivers are on during the conversion and a 13th clock cycle is needed for the last bit of the conversion result. Three more clock cycles are needed to complete the last byte (DOUT will be low), which are ignored by the converter. Control Byte The control byte (on DIN), as shown in Table 3, provides the start conversion, addressing, ADC resolution, configuration, and power-down of the A8946. Table 3 and Table 4 give detailed information regarding the order and description of these control bits within the control byte. Table 3 Order of the Control Bits in the Control Byte Bit7 (MSB) Bit6 Bit5 Bit4 Bit3 Bit2 Bit1 Bit0 (LSB) S A2 A1 A0 MODE SER / PD1 PD0

AiT Semiconductor Inc. www.ait-ic.com A8946 TOUCH SCREEN DRIVER 4-WIRE RESISTANCE, LOW-VOL TAGE I/O INTERFACE REV1.3 - DEC 2007 RELEASED, JAN 2014 UPDATED - - 15 - Table 4 Descriptions of the Control Bits in the Control Byte Initiate START - The first bit, the S bit, must always be high and initiates the start of the control byte. The A8946 ignores inputs on the DIN pin until the start bit is detected. Addressing- The next three bits (A2, A1, and A0) select the active input channel(s) of the input multiplexer (see Tables 1 & 2), touch screen drivers, and the reference inputs. MODE- The mode bit sets the resolution of the ADC. With this bit low, the next conversion has 12 bits of resolution, whereas with this bit high, the next conversion has 8 bits of resolution. SER / DFR -SER/ bit controls the reference mode, either single-ended (High) or differential (Low). The differential mode is also referred to as the ratio metric conversion mode and is performance. The reference is derived from the voltage at the switch drivers, which is almost the same as the voltage to the touch screen. In this case, a reference voltage is not needed as the reference voltage to the ADC is the voltage across the touch screen. In the single-ended mode, the converter reference voltage is always the difference between the VREF and GND pins. Bit Symbol Description 7 S Start bit. Control byte starts with first high bit on DIN. A new control byte can start every 15th clock cycle in 12-bit conversion mode or every 11th clock cycle in 8-bit conversion mode (see Fig. 11). 6-4 A2-A0 Channel Select bits. Along with the SER/ bit, these bits control the setting of the multiplexer input, touch driver switches, and reference inputs (See Table 1 and Table 2)

3 MODE

12-Bit/8-Bit Conversion Select bit. This bit controls the number of bits for the nest conversion：12-bits (Low) or 8-bits (High)

2 SER/

Single-Ended/Differential Reference Select bit. Along with bits A2 -A0, this bit controls the setting of the multiplexer input, touch driver switches, and reference 1-0 PD1-PD0 Inputs (see Table 1 and Table 2). Power-Down Mode Select bits. Refer to Table 5 for details.

AiT Semiconductor Inc. www.ait-ic.com A8946 TOUCH SCREEN DRIVER 4-WIRE RESISTANCE, LOW-VOL TAGE I/O INTERFACE REV1.3 - DEC 2007 RELEASED, JAN 2014 UPDATED - - 16 - If X-Position, Y-Position, and Pressure-Touch are measured in the single-ended mode, an external reference voltage is needed. The A8946 must also be powered from the external reference. Caution should be observed when u sing the single -ended mode such that the input voltage to the ADC dose not exceeds the internal reference voltage, especially if the supply voltage is greater than 2.7V. Note：The differential mode can only be used for X-Position, Y-Position, and Pressure-touch measurements. All other measurements require the single-ended mode. PD0 and PD1 -Table 5 describe the power -down and the internal reference voltage configurations. The internal reference voltage can be turned on or off independently of the ADC. This can allow extra time for the internal reference voltage to settle to the final value prior to making a conversion. Make sure to also allow this extra wake-up time if the internal reference is powered down. The ADC requires no wake -up time and can be instantaneously used. Also note that the status of the internal reference power -down is latched into the part (internally) with BUSY going high. In order to turn the reference off, an additional write to the A8946 is required after the channel has been converted. Fig. 7 Conversion Timing, 24 Cl ocks-per-Conversion, 8-Bit Bus Interface. No DCLK delay requ ired with dedicated serial port

AiT Semiconductor Inc. www.ait-ic.com A8946 TOUCH SCREEN DRIVER 4-WIRE RESISTANCE, LOW-VOL TAGE I/O INTERFACE REV1.3 - DEC 2007 RELEASED, JAN 2014 UPDATED - - 17 - Table 5 Power-Down and Internal Reference Selection PD1 PD0 PENIRQ Description 0 0 Enabled Power-Down Between Conversions. When each conversion is finished, the converter enters a low-power mode. At the start of the next conversion, the device instantly powers up to full power. There is no need for additional delays to ensure full operation, and the very first conversion is valid. The Y – switch is on when in power-down. 0 1 Disabled Reference is off and ADC is on. 1 0 Enabled Reference is on and ADC is off. 1 1 Disabled Device is always powered. Reference is on and ADC is ON. PENIRQ OUTPUT The pen-interrupt output function is shown in Fig . 8 while in power-down mode with PD0 = 0, the Y – driver is on and connects the Y-plane of the touch screen to GND. The PENIRQ output is connected to the X+ input through two transmission gates. When the screen is touched, the X+ input is pulled to ground through the touch screen. In most of the A8946 models, the internal pull-up resistor value is nominally 50KΩ, but this may vary between 36K and 67K Ω given process and temperature variations. In order to assure a logic low of 0.35V DD is presented to the PENIRQ circuitry, the total resistance between the X+ and Y - terminals must b e less than 21KΩ. The -90 version of the A8946 uses a nominal 90KΩ pull-up resistor, which allows the total resistance between the X+ and Y - terminals to be as high as 30KΩ. Note that the higher pull -up resistance will cause a slower response time of the PENIRQ to a screen touch, so user software should take this into account. The PENIRQ output goes low due to the current path through the touch screen to ground, which initiates an interrupt to the processor. During the measurement cycle for X -, Y -, and Z -Position, the X+ input is disconnected from the PENIRQ internal pull-up resistor. This is done to eliminate any leakage current from the internal pull-up resistor through the touch screen, thus causing no errors.

AiT Semiconductor Inc. www.ait-ic.com A8946 TOUCH SCREEN DRIVER 4-WIRE RESISTANCE, LOW-VOL TAGE I/O INTERFACE REV1.3 - DEC 2007 RELEASED, JAN 2014 UPDATED - - 18 - Fig. 8 PENIRQ Functional Block Diagram Furthermore, the PENIRQ output is disabled and low during the measurement cycle for X-, Y-, and Z-Position. The PENIRQ output is disabled and high during the measurement cycle for battery monitor, auxiliary input, and chip temperature. If the last control byte written to the A8946 contains PD0 = 1, the pen -interrupt output function is disabled and is not able to detect when the screen is touched. In order to re -enable the pen-interrupt output function under these circumstances, a control byte n eeds to be written to the A8946 with PD0 = 0. If the last control byte written to the A8946 contains PD0 = 0, the pen -interrupt output function is enabled at the end of the conversion. The end of the conversion occurs on the falling edge of DCLK after bit 1 of the converted data is clocked out of the A8946. It is recommended that the processor mask the interrupt PENIRQ is associated with whenever the processor sends a control byte to the A8946. This prevents false triggering of interrupts when the PENIRQ output is disabled in the cases discussed in this section.

AiT Semiconductor Inc. www.ait-ic.com A8946 TOUCH SCREEN DRIVER 4-WIRE RESISTANCE, LOW-VOL TAGE I/O INTERFACE REV1.3 - DEC 2007 RELEASED, JAN 2014 UPDATED - - 19 - Fig. 9 Conversion Timing, 16 Clocks-per-Conversion, 8-Bit Bus Interface. No DCLK delay required with dedicated serial port

16 Clocks-per-Conversion

The control bits for conversion n + 1 can be overlapped with conversion n to allow for a conversion every 16 clock cycles, as shown in Fig . 9. This figure also shows possible serial communication occurring with other serial peripherals between each byte transfer from the processor to the converter. This is possible, provided that each conversion completes within 1.6ms of starting. Otherwise, the signal that is captured on the input sample-and-hold may droop enough to affect the conversion result. Note that the A8946 is fully powered while other serial communications are taking place during a conversion. Table 6 Timing Specifications, TA= –40°C to +85°C

AiT Semiconductor Inc. www.ait-ic.com A8946 TOUCH SCREEN DRIVER 4-WIRE RESISTANCE, LOW-VOL TAGE I/O INTERFACE REV1.3 - DEC 2007 RELEASED, JAN 2014 UPDATED - - 20 - Fig. 10 Detailed Timing Diagram Fig.11 Maximum Conversion Rate, 15 Clocks-per-Conversion Digital Timing Fig. 7and 10 and Table 6 provide detailed timing for the digital interface of the A8946.

AiT Semiconductor Inc. www.ait-ic.com A8946 TOUCH SCREEN DRIVER 4-WIRE RESISTANCE, LOW-VOL TAGE I/O INTERFACE REV1.3 - DEC 2007 RELEASED, JAN 2014 UPDATED - - 21 -

15 Clocks-per-Conversion

Fig. 12 Ideal Input Voltages and Output Codes Notes：(1) Reference Voltage at Converter. +REF-(-REF) (2) Input Voltage at converter, after Multiplexer. +IN-(-IN) Fig. 11 provides the fastest way to clock the A8946. This method does not work with the serial interface of most microcontrollers and digital signal processors, as they are generally not capable of providing 15 clock cycles per serial transfer. However, this method can be used with field programmable gate arrays (FPGAs) or application specific integrated circuits (ASICs). Note that this effectively increases the maximum conversion rate of the converter beyond the values given in the specification tables, which assu me 16 clock cycles per conversion. Data Format The A8946 output data is in Straight Binary format, as shown in Fig .12. The Fig . 12 shows the ideal output code for the given input voltage and does not include the effects of offset, gain, or noise.

AiT Semiconductor Inc. www.ait-ic.com A8946 TOUCH SCREEN DRIVER 4-WIRE RESISTANCE, LOW-VOL TAGE I/O INTERFACE REV1.3 - DEC 2007 RELEASED, JAN 2014 UPDATED - - 22 - 8-Bit Conversion The A8946 provides an 8 -bit conversion mode that can be used when faster throughput is needed and the digital result is not as critical. By switching to the 8-bit mode, a conversion is complete four clock cycles earlier. Not only does this short en each conversion by four bits (25% faster throughput), but each conversion can actually occur at a faster clock rate. This is because the internal settling time of the A8946 is not as critical—settling to better than 8 bits is all that is needed. The clo ck rate can be as much as 50% faster. The faster clock rate and fewer clock cycles combine to provide a 2x increase in conversion rate. Power Dissipation There are two major power modes for the A8946: full-power (PD0 = 1) and auto power-down (PD0 = 0). When operating at full speed and 16 clocks-per-conversion (see Fig.9), the A8946 spends most of the time acquiring or converting. There is little time for auto power -down, assuming that this mode is active. Therefore, the difference between full-power mode and auto power-down is negligible. If the conversion rate is decreased by slowing the frequency of the DCLK input, the two modes remain approximately equal. However, if the DCLK frequency is kept at the maximum rate during a conversion but conversions are done less often, the difference between the two modes is dramatic. CS also puts the A8946 into power -down mode. When CS goes high, the A8946 immediately goes into power-down mode and does not complete the current conversion. The internal reference, however, does not turn off with CS going high. To turn the reference off, an additional write is required before CS goes high (PD1 = 0). When the A8946 first powers up, the device draws about 20μA of current until a control byte is written to it with PD0 = 0 to put it into power -down mode. This can be avoided if the A8946 is powered up with CS = 0 and DCLK = IOVDD.

AiT Semiconductor Inc. www.ait-ic.com A8946 TOUCH SCREEN DRIVER 4-WIRE RESISTANCE, LOW-VOL TAGE I/O INTERFACE REV1.3 - DEC 2007 RELEASED, JAN 2014 UPDATED - - 23 - PACKAGING INFORMATION Dimension in QFN16 Package (Unit: mm) Top View Bottom View Side View Symbol Min Max A 0.80 0.90 A1 0.01 0.09 D 3.90 4.10 E 3.90 4.10 D1 2.30 (REF) E1 2.30 (REF) b 0.18 0.28 e 0.65 (BSC) L 0.50 0.60 L1 0.00 0.05

AiT Semiconductor Inc. www.ait-ic.com A8946 TOUCH SCREEN DRIVER 4-WIRE RESISTANCE, LOW-VOL TAGE I/O INTERFACE REV1.3 - DEC 2007 RELEASED, JAN 2014 UPDATED - - 24 - IMPORTANT NOTICE AiT Semiconductor Inc. (AiT) reserves the right to make changes to any its pr oduct, specifications, to discontinue any integrated circuit product or service without notice, and advises its customers to obtain the latest version of relevant information to verify, before plac ing orders, that the information being relied on is current. AiT Semiconductor Inc.'s integrated circuit products are not designed, intended, authorized, or warranted to be suitable for use in life support applications, devices or systems or other critical applications. Use of AiT products in such applications is understood to be fully at the risk of the customer. As used herein may involve potential risks of death, personal injury, or servere property, or environmental damage. In order to minimize risks associated with the customer's applications, the customer should provide adequate design and operating safeguards. AiT Semiconductor Inc. assumes to no liability to customer product design or application support. AiT warrants the performance of its products of the specifications applicable at the time of sale.

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TOUCH SCREEN DRIVER 4-WIRE RESISTANCE, LOW-VOLTAGE I/O INTERFACE REV1.3

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