MAXQ7667AACM/V+T【PDF 11/40 页】IC MCU-BASED DAS 16BIT 48-LQFP

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MAXQ7667

16-Bit, RISC, Microcontroller-Based,

Ultrasonic Distance-Measuring System

______________________________________________________________________________________

output to the FIFO automatically each time the lowpass

filter output updates, through the control of one of the

timer outputs, or through software. The device includes

a FIFO depth counter with programmable interrupt lev-

els and generates an interrupt if a FIFO overflow condi-

tion occurs. The output of the digital lowpass filter

connects to a digital comparator that can generate an

interrupt for a specified echo signal level.

Digital Comparator and Threshold Adjust

The digital comparator output asserts when the echo

amplitude at the output of the digital lowpass filter cross-

es a given threshold. The comparator’s threshold level,

hysteresis, and interrupt polarity are programmable.

SAR ADC

The MAXQ7667 incorporates a 12-bit unbuffered SAR

ADC with sample-and-hold and conversion rate up to

250ksps. The ADC allows measurements of tempera-

ture, battery voltage, or other parameters using five sin-

gle-ended or two fully differential analog inputs

(AIN0–AIN4). All of the analog inputs have a range of 0

to VREF in unipolar mode and ±VREF/2 in bipolar mode.

The SAR ADC supports three different conversion start

sources: timers, ADC control input (ADCCTL), and soft-

ware write. The conversion start source triggers the

ADC acquisition and conversion. The system clock pro-

vides the ADC clock frequency programmable to 1/2,

1/4, 1/8, or 1/16 of the system clock. Use internal

bandgap reference, external reference, or AVDD for

voltage reference of the SAR ADC. Figure 3 shows a

simplified block diagram of the SAR ADC.

The output of the SAR ADC is straight binary in unipolar

mode and two’s complement in bipolar mode. Figures 4

and 5 show the ADC transfer functions in unipolar

mode and bipolar mode.

000

001

002

003

004

FFC

FFB

FFD

FFE

FFF

FS - 1.5 LSB

FULL-SCALE

TRANSITION

FS = REF

ZS = 0

1 LSB = REF/4096

OUTPUT

CODE

(hex)

DIFFERENTIAL INPUT VOLTAGE (LSB)

Figure 4. Unipolar Transfer Function

800

801

FFE

001

000

FFF

7FE

7FF

-FS

+FS

OUTPUT

CODE

(hex)

DIFFERENTIAL INPUT VOLTAGE (LSB)

+FS - 1.5 LSB

FULL-SCALE

TRANSITION

+FS = REF/2

ZS = 0

-FS = -REF/2

1 LSB = REF/4096

-FS + 0.5 LSB

Figure 5. Bipolar Transfer Function

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