MXB7846 查看數據表（PDF） - Maxim Integrated

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MXB7846

2.375V to 5.25V, 4-Wire Touch-Screen Controller with Internal Reference and Temperature Sensor

Maxim Integrated 

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

with Internal Reference and Temperature Sensor

Detailed Description

The MXB7846 uses a successive-approximation conver-

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

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

interface provides easy communication to a micro-

processor (µP). It features an internal 2.5V reference, an

on-chip temperature sensor, a battery monitor, and a

4-wire touch-screen interface (Functional Diagram).

Analog Inputs

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

tion that includes the input multiplexer of the MXB7846,

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-, AUX, BAT, and the

internal temperature sensor.

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.

PENIRQ

TEMP1

TEMP0

+VDD

VREF

MXB7846

A2–A0

(SHOWN 001B)

SER/DFR

(SHOWN HIGH)

X+

X-

REF ON/OFF

Y+

Y-

+IN REF+

12-BIT ADC

2.5V

-IN REF-

REFERENCE

7.5kΩ

VBAT

2.5kΩ

BATTERY

ON

AUX

GND

Figure 2. Equivalent Input Circuit

MICROWIRE is a trademark of National Semiconductor Corp.

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