Datasheet

Circuit Description

3-7

Operation

Likewise, the I

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

J11 or by the USB audio controller (U5).

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 JMP3, turn off SW1-1 and SW1-2, and cycle

power to the TSC2100EVM in order to use the external I

S bus.

3.4.2 Power Supply

Power to the TSC2100EVM can be derived directly from the USB interface or

externally supplied through the J9 terminal block or the J10 barrel jack

connector. Supply voltages of 6 VDC to 10 VDC must be supplied from an

external supply. Since it is regulated on the TSC2100EVM, 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.

U6 regulates the input supply voltage to provide 1.8 V for the TSC2100’s digital

core and 3.3 V for the remaining hardware. The regulated supply voltages

have LEDs attached that alert the user that the supply is working. D4 (red) is

the indicator for the 1.8-V power supply and D3 (green) is the indicator for the

3.3-V power supply.

3.4.3 Touch Screen and Analog Inputs

Terminal block J3 provides input connection points for the battery and auxiliary

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

range from 0 V to V

reg

. The touch screen can be connected to J2 or to the J1

terminal block.

Each of these seven inputs to the TSC2100 internal touch screen ADC circuitry

has a provision for an RC filter to be placed in line with the signal. As shipped,

all of the resistors are 0 Ω and the capacitor is 0.01 µF for C4 and not installed

for C1 to C3 and C5 to C7. If noisy conditions prevent obtaining good readings

from the TSC2100, 0.01-µF to 0.1-µF capacitors can be installed in positions

C1 through C4. 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.

3.4.4 Voltage Reference

The TSC2100 has an internal voltage reference, selectable at 1.25 V or 2.5

V. If an external reference is preferred, the external voltage can be input from

J4.