MXB7846(2004) 查看數據表（PDF） - Maxim Integrated

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MXB7846
(Rev.:2004)

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

the MXB7846 to initiate a conversion, the MXB7846

biases the touch screen through the internal switches at

the beginning of the acquisition period. The voltage

transient at the touch screen needs to settle down to a

stable voltage before the acquisition period is over.

After the acquisition period is over, the A/D converter

goes into a conversion period with all internal switches

turned off if the device is in single-ended mode. If the

device is in differential mode, the internal switches

remain on from the start of the acquisition period to the

end of the conversion period.

Power-On Reset

When power is first applied, internal power-on circuitry

resets the MXB7846. Allow 10µs for the first conversion

after the power supplies stabilize. If CS is low, the first

logic 1 on DIN is interpreted as a start bit. Until a con-

version takes place, DOUT shifts out zeros. On power-

up, allow time for the reference to stabilize.

Power Modes

Save power by placing the converter in one of two low-

current operating modes or in full power down between

conversions. Select the power-down mode through

PD1 and PD0 of the control byte (Tables 3 and 4).

The software power-down modes take effect after the

conversion is completed. The serial interface remains

active while waiting for a new control byte to start a con-

version and switches to full-power mode. After complet-

ing its conversion, the MXB7846 enters the programmed

power mode until a new control byte is received.

OUTPUT CODE

11…111

11…110

11…101

FULL-SCALE

TRANSITION

FS = (VREF+ - VREF-)

(VREF+ - VREF-)

1LSB = 4096

00…011

00…010

00…001

00…000

01 23

FS

FS-3/2LSB

INPUT VOLTAGE (LSB) = [(V+IN) - (V-IN)]

Figure 12. Ideal Input Voltages and Output Codes

The power-up wait before conversion period is depen-

dent on the power-down state. When exiting software

low-power modes, conversion can start immediately

when running at decreased clock rates. Upon power-

on reset, the MXB7846 is in power-down mode with

PD1 = 0 and PD0 = 0. When exiting software shutdown,

the MXB7846 is ready to perform a conversion in 10µs

with an external reference. When using the internal ref-

erence, allow enough time for reference to settle to 12-

bit accuracy when exiting full power-down mode, as

shown in the Typical Operating Characteristics.

PD1 = 1, PD0 = 1

In this mode, the MXB7846 is always powered up and

both the reference and the ADC are always on. The

device remains fully powered after the current conver-

sion completes.

PD1 = 0, PD0 = 0

In this mode, the MXB7846 powers down after the cur-

rent conversion completes or on the next rising edge of

CS, whichever occurs first. The next control byte

received on DIN powers up the MXB7846. At the start

of a new conversion, it instantly powers up. When each

conversion is finished, the part enters power-down

mode, unless otherwise indicated. The first conversion

after the ADC returns to full power is valid for differen-

tial conversions and single-ended measurement con-

versions when using an external reference.

When operating at full speed and 16 clocks per conver-

sion, the difference in power consumption between

PD1 = 0, PD0 = 1, and PD1 = 0, PD0 = 0 is negligible.

Also, in the case where the conversion rate is

decreased by slowing the frequency of the DCLK input,

the power consumption between these two modes is

not very different. When the DCLK frequency is kept at

the maximum rate during a conversion, conversions are

done less often. There is a significant difference in

power consumption between these two modes.

PD1 = 1, PD0 = 0

In this mode, the MXB7846 is powered down. This

mode becomes active after the current conversion

completes or on the next rising edge of CS, whichever

occurs first. The next command byte received on the

DIN returns the MXB7846 to full power. The first conver-

sion after the ADC returns to full power is valid.

PD1 = 0, PD0 = 1

This mode turns the internal reference off and leaves

the ADC on to perform conversions using an external

reference.

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