Datasheet

Circuit Description

3-7

Operation

Do not drive the external SPI bus when the firmware is loaded and

the onboard microprocessor is active. Disable the micro-

processor by removing JMP6 and cycling power to the

TSC2301EVM if you want to use the external SPI bus.

Each signal from the SPI inputs is connected directly to the TSC2301. As such,

signals on these pins must not exceed the power supply voltage of the

TSC2301, which is 3.3 V on this EVM.

Likewise, the I

S signals for the digital audio can be driven either externally by

J10 or by the USB audio controller.

Do not drive the external I

S bus when the firmware is loaded and

the onboard microprocessor is active. Disable the micro-

processor by removing JMP6 and cycling power to the

TSC2301EVM if you want to use the external I

S bus.

3.3.2 Power Supply

Power to the TSC2301EVM can be derived directly from the USB interface,

or externally supplied through the J8 terminal block or the J9 barrel jack

connector. 6 VDC to 12 VDC must be supplied from an external supply. Since

it is regulated on the TSC2301EVM, this input voltage does not need to be

regulated, as long as it falls within this range. D1 prevents damage to the board

in the event a power supply is connected in reverse polarity.

U5 regulates the input supply voltage to provide 3.3 V. The regulated supply

voltage has an LED attached that alerts the user that the supply is working.

3.3.3 Touch Screen and Analog Inputs

Terminal block J14 provides input connection points for the battery and

auxiliary inputs. Battery inputs may range from 0 V to 6 V, and the auxiliary

inputs can range from 0 V to 2.5 V. The touch screen can be connected to J13,

or to the J12 terminal block.

Each of these eight inputs has provision for an RC filter to be placed in line with

the signal. As shipped, all the resistors are 0 Ω, and the capacitors are not

installed. If noisy conditions prevent obtaining good readings from the

TSC2301, 0.1-µF capacitors may be installed in positions C39 through C46.

If more filtering is required, the 0-Ω resistors should be unsoldered from the

board and replaced with small resistors. Note that increasing the capacitance

on the touch screen inputs requires increased panel voltage stabilization time

and increased precharge and sense times, thus lowering the available number

of readings per second.