BL2046

Figure 3. Diagram of Differential Reference (SER/

low, Y switches enabled, X+ is

analog input).

Touch Screen Setting

In some applications, external capacitors may be required across the touch screen for filtering

noise picked up by the touch screen. These capacitors provide a low-pass filter to reduce the noise,

but cause a settling time requirement when the panel is touched that typically shows up as a gain

error. There are several methods for minimizing or eliminating this issue. The problem is the input

and/or reference has not settled to the final steady-state value prior to the ADC sampling the

input(s) and providing the digital output. Additionally, the reference voltage may still be changing

during the measurement cycle. Option 1 is to stop or slow down the BL2046 DCLK for the

required touch screen settling time. This allows the input and reference to have stable values for

single-ended and the differential modes. Option 2 is to operate the BL2046 in the differential

mode only for the touch screen measurements and command the BL2046 to remain on (touch

screen drivers ON) and not go into power-down (PD0 = 1). Several conversions are made

depending on the settling time required and the BL2046 data rate. Once the required number of

conversions have been made, the processor commands the BL2046 to go into its power-down state

on the last measurement. This process is required for X-Position, Y-Position, and Z-Position

measurements. Option 3 is to operate in the 15 Clock-per-Conversion mode, which overlaps the

analog-to-digital conversions and maintains the touch screen drivers on until commanded to stop

Tempeature Mesurement

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