maxq7667 Maxim Integrated Products, Inc., maxq7667 Datasheet - Page 19

• Manufacturer Part Number: maxq7667
• Description: 16-bit, Risc, Microcontroller-based, Ultrasonic Distance-measuring System
• Manufacturer: Maxim Integrated Products, Inc.

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.
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.
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-
Figure 4. Unipolar Transfer Function
FFD
FFC
FFE
FFB
FFF
004
003
002
001
000
0
FS = REF
ZS = 0
1 LSB = REF/4096
1
Digital Comparator and Threshold Adjust
2
DIFFERENTIAL INPUT VOLTAGE (LSB)
______________________________________________________________________________________
3
Ultrasonic Distance-Measuring System
4
16-Bit, RISC, Microcontroller-Based,
FULL-SCALE
TRANSITION
FS - 1.5 LSB
SAR ADC
FS
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 V
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.
Figure 5. Bipolar Transfer Function
REF
7FF
7FE
001
000
FFF
800
FFE
801
in unipolar mode and ±V
+FS = REF/2
ZS = 0
-FS = -REF/2
1 LSB = REF/4096
-FS
-FS + 0.5 LSB
DIFFERENTIAL INPUT VOLTAGE (LSB)
FULL-SCALE
TRANSITION
0
REF
+FS - 1.5 LSB
/2 in bipolar mode.
+FS
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