DC Electrical Characteristics (0˚C

≤ T

Datasheet min/max specification limits are guaranteed by design, test, or statistical analysis.

Parameter

Conditions

Min

Typ

Max

Units

Input Capacitance

7pF

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

HALT is done with device neither sourcing nor sinking current; all inputs tied

Note 7: Absolute Maximum Ratings should not be exceeded.

A/D Converter Electrical Characteristics (0˚C

≤ T

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

LSB

DNL

V

LSB

INL

V

LSB

INL

V

LSB

Offset Error

V

LSB

Offset Error

V

LSB

Gain Error

V

LSB

Gain Error

V

LSB

Input Voltage Range

2.7V

≤ V

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

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.

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