1. General Description:

️· The AK4187 is a mixed-mode analog-to-digital converter (ADC) and resistive touch screen controller IC.
️· It combines a 12-bit SAR ADC, a 4-wire (expandable to 6-wire for dual touch) resistive touch screen interface, a calculator, an internal clock generator, and an I2C interface.
️· It's designed for applications like touch screen devices, portable devices, and measurement systems.

2. Key Features:

️· ADC:
- 12-bit resolution.
- SAR (Successive Approximation Register) architecture.
- Continuous conversion mode.
️· Touch Screen Controller:
- Supports 4-wire resistive touch screens.
- Dual-touch capability through the use of RXP, RYP pins, enabling more complex gestures.
- Uses external resistors (R1-R4) to achieve dual-touch functionality.
️· I2C Interface: Standard I2C for communication with a host microcontroller.
️· Internal Clock Generator: Reduces external component count.
️· Calculator: Integrated calculator for processing data.
️· Operating Voltage: 2.7V to 3.6V (for most functions), 1.6V to 3.6V (for some signals)
️· Low Power Consumption: Optimized for battery-powered devices.

3. Pin Configuration & Connections (Critical for Implementation):

️· XP, XN: Connect to the X-axis contacts of the resistive touch screen. XN requires an external resistor (R4).
️· YP, YN: Connect to the Y-axis contacts of the resistive touch screen. YN requires an external resistor (R3).
️· RXP, RYP: Additional pins for dual-touch capabilities. They connect to the touch screen through resistors R2 and R1, respectively.
️· CAD0: This pin needs to be connected to TVDD if it's set to "H."
️· Standard I2C pins: SDA, SCL for communication.
️· ADC input: Analog input for conversion.
️· Internal Clock output: Allows external clock source if needed.

4. Timing Characteristics (Important for Proper Operation):

️· I2C Timing:
- SCL frequency up to 400 kHz.
- Various setup and hold times for SDA and SCL signals.
- Setup time for repeated start condition.
️· ADC Conversion Timing:
- Internal clock frequency range: 2.5 MHz to 5.1 MHz.

5. Dual-Touch Functionality (Key Differentiator):

️· The AK4187 expands beyond a standard 4-wire touch screen interface.
️· It adds RXP and RYP pins, connected through external resistors (R1 & R2), allowing for more complex touch gestures and dual-touch detection.
️· Resistor Values: The external resistor values (R1-R4) are *critical* and need to be carefully chosen based on the touch panel's resistance characteristics. The document recommends tolerances of ±20%.
️· Resistor values are:
- R1 = 75% of Y-axis resistance.
- R2 = 75% of X-axis resistance.
- R3 = 1/4 of Y-axis resistance.
- R4 = 1/4 of X-axis resistance.

6. Operational Overview:

️· The AK4187 integrates various functions, simplifying the design of touch-enabled devices.
️· The connection diagram demonstrates how the IC connects to the touch panel, external resistors, and host microcontroller.

7. Important Notes/Cautions:

️· CAD0 pin: Must be connected to TVDD if it's set to “H.”
️· Resistor Selection: The accuracy of external resistors (R1-R4) is vital for reliable dual-touch operation.
️· Refer to the detailed timing diagrams for precise signal timing requirements.
️· This document provides general information; detailed application notes and design guidelines may be available separately.



Key Takeaways / Things to Remember:

️· Dual-Touch is a Feature: The extended 6-wire interface and RXP/RYP pins allow for a significantly enhanced touch experience beyond simple single-touch functionality.
️· Resistors are Paramount: Getting the external resistor values correct is absolutely essential for reliable dual-touch performance. Measure your touch panel's resistance and calculate the appropriate resistor values.
️· I2C Timing Matters: Pay close attention to the I2C timing parameters to ensure proper communication with the host microcontroller.
️· Read the Diagrams Carefully: The connection diagrams and timing diagrams are critical for successful implementation.