MXB7843(2002) Ver la hoja de datos (PDF) - Maxim Integrated

Número de pieza

componentes Descripción

Fabricante

MXB7843
(Rev.:2002)

2.375V to 5.25V, 4-Wire Touch-Screen Controller

Maxim Integrated 

2.375V to 5.25V, 4-Wire Touch-Screen

Controller

Detailed Description

The MXB7843 uses a successive-approximation conver-

sion technique to convert analog signals to a 12-bit digital

output. An SPI/QSPI/MICROWIRE™-compatible serial

interface provides an easy communication to a micro-

processor (µP). It features a 4-wire touch-screen interface

and two auxiliary ADC channels (Functional Diagram).

Analog Inputs

Figure 2 shows a block diagram of the analog input sec-

tion that includes the input multiplexer of the MXB7843,

the differential signal inputs of the ADC, and the differ-

ential reference inputs of the ADC. The input multiplexer

switches between X+, X-, Y+, Y-, IN3, and IN4.

In single-ended mode, conversions are performed using

REF as the reference. In differential mode, ratiometric

conversions are performed with REF+ connected to X+ or

Y+, and REF- connected to X- or Y-. Configure the refer-

ence and switching matrix according to Tables 1 and 2.

During the acquisition interval, the selected channel

charges the sampling capacitance. The acquisition

interval starts on the fifth falling clock edge and ends

on the eighth falling clock edge.

The time required for the T/H to acquire an input signal

is a function of how quickly its input capacitance is

charged. If the input signal’s source impedance is high,

the acquisition time lengthens, and more time must be

allowed between conversions. The acquisition time

(tACQ) is the maximum time the device takes to acquire

the input signal to 12-bit accuracy. Calculate tACQ with

the following equation:

tACQ = 8.4 × (RS + RIN ) × 25pF

where RIN = 2kΩ and RS is the source impedance of

the input signal.

Source impedances below 1kΩ do not significantly

affect the ADC’s performance. Accommodate higher

source impedances by either slowing down DCLK or

by placing a 1µF capacitor between the analog input

and GND.

Input Bandwidth and Anti-Aliasing

The ADCs input tracking circuitry has a 25MHz small-

signal bandwidth, so it is possible to digitize high-

speed transient events. To avoid high-frequency sig-

nals being aliased into the frequency band of interest,

anti-alias filtering is recommended.

CS

tCH

tCSS

tCP

tCSH

tCL

DCLK

DIN

DOUT

tDS

tDH

tDV

tDO

tTR

tBDV

tBTR

BUSY

tBD

Figure 1. Detailed Serial Interface Timing

MICROWIRE is a trademark of National Semiconductor Corp.

8 _______________________________________________________________________________________

Share Link: