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LM8300 Datasheet(PDF) 8 Page - National Semiconductor (TI) |
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LM8300 Datasheet(HTML) 8 Page - National Semiconductor (TI) |
8 / 20 page 8.0 Electrical Characteristics (Continued) DC Electrical Characteristics (0˚C ≤ T A ≤ +70˚C) (Continued) Datasheet min/max specification limits are guaranteed by design, test, or statistical analysis. Parameter Conditions Min Typ Max Units Input Capacitance 7pF Note 4: Maximum rate of voltage change must be < 0.5 V/ms. Note 5: Supply and IDLE currents are measured with CKI driven with a square wave Oscillator, CKO driven 180˚ out of phase with CKI, inputs connected to VCC and outputs driven low but not connected to a load. Note 6: The HALT mode will stop CKI from oscillating. Measurement of IDD HALT is done with device neither sourcing nor sinking current; all inputs tied to VCC; A/D converter and clock monitor and BOR disabled. Note 7: Absolute Maximum Ratings should not be exceeded. A/D Converter Electrical Characteristics (0˚C ≤ T A ≤ +70˚C) (Single-ended mode only) Datasheet min/max specification limits are guaranteed by design, test, or statistical analysis. Parameter Conditions Min Typ Max Units Resolution 10 Bits DNL V CC =5V ±1 LSB DNL V CC =3V ±1 LSB INL V CC =5V ±2 LSB INL V CC =3V ±4 LSB Offset Error V CC =5V ±1.5 LSB Offset Error V CC =3V ±2.5 LSB Gain Error V CC =5V ±1.5 LSB Gain Error V CC =3V ±2.5 LSB Input Voltage Range 2.7V ≤ V CC < 5.5V 0 V CC V Analog Input Leakage Current 0.5 µA Analog Input Resistance (Note 8) 6k Ω Analog Input Capacitance 7pF Operating Current on AV CC AV CC = 5.5V 0.2 0.6 mA Note 8: Resistance between the device input and the internal sample and hold capacitance. 9.0 Functional Description 9.1 GENERAL The LM8300/8500 is a 4-wire resistive touch screen control- ler. The primary communication is through the built in UART operating at a baud rate of 38400. The LM8300/8500 has the ability to measure pressure on the Z-axis, in addition to the X-Y coordinates. The device has the capability to do a 2, 5, and 13 point calibration. All calibration data is stored in the internal non- volatile storage element. In addition, all settings pertaining to the controller are stored internally. This feature negates the need for external EEPROM. The device has three built in averaging algorithms: oversam- pling, delta, and focus. These algorithms help to minimize noise and A/D variation due to noise. Refer to the averaging algorithm section for a more detail explanation. These algo- rithms are implemented on-chip, freeing the main processor from these tasks. To further minimize noise in extremely noisy environments, the device has the ability to route the signal from the touch panel to an external filtering stage before A/D conversions are performed. To minimize power consumption, the device can be put into power save mode. The device can be set to go into power save mode automatically or manually by pulling the external shutdown pin low. 9.2 ADVANCED PIN DESCRIPTIONS CLK_SET — This pin is the selection pin used to determine the operating frequency of the controller. On power up, the controller polls this pin to determine if the operating fre- quency is set to 10 MHz or 3.3 MHz. If the pin is left floating or tied high, then the operating frequency is 10 MHz. If the pin is tied low, then the operating frequency is set to 3.3 MHz. Note: This is available on the LM8500 only. SHUTDOWN — This is the external shut down pin. When pulled low, the controller goes into power saving mode. This selection pin state has higher priority than the internal power save mode settings. WAKE_UP — This pin is used to wake the controller from power save mode. When the device is in power save mode, the pin must be tied to one of X-Y lines coming from the touch screen panel. X+ — Connect to X+ terminal of the resistive screen. X- — Connect to X- terminal of the resistive screen. Y+ — Connect to Y+ terminal of the resistive screen. Y- — Connect to Y- terminal of the resistive screen. Filter_out — Analog output to external filter. The use of the external filter is controlled by sending a command byte of $A0 on the UART to the controller. Filter_in — Analog input from external filter. The use of the external filter is controlled by sending a command byte of $A0 on the UART to the controller. www.national.com 8 |
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