LM8300-REF-01 National Semiconductor, LM8300-REF-01 Datasheet - Page 22

• Manufacturer Part Number: LM8300-REF-01
• Description: BOARD EVALUATION LM8300
• Manufacturer: National Semiconductor

Specifications of LM8300-REF-01

• Main Purpose: Interface, Touch Screen Controller
• Utilized Ic / Part: LM8300
• Lead Free Status / RoHS Status: Not applicable / Not applicable
• Secondary Attributes: -
• Embedded: -
• Primary Attributes: -

Analog supply voltage
The analog ground and voltage is used to power the analog block in the device as well as
providing the reference voltage for A/D. For the A/D to operate properly, AVCC must be equal
to VCC.
If the analog power supply is to be derived from the VCC, then the analog power supply should
have sufficient filtering available. The simplest filter method is to decouple the VCC before
connecting to the AVCC pin. This can be accomplished by the use of a RC filter. Figure 3
shows a typical connection. If desired, ferrite beads can be used between the analog ground
(AGND) and digital ground (GND) to control ground current. Another method is to provide an
analog ground plane.
RS232 Connector
The device uses the RS232 protocol to communicate with the touch screen (TS) driver. To
minimize the cost of the board and to demonstrate the low cost components that can be used to
drive the RS232 connection, three BJTs are used. Although it is possible to use a RS232 driver
chip, the use of BJTs are lower in cost. Figure 4 shows the RS232 circuitry.
Fig. 2
Fig. 3