LTC1289BCSW View Datasheet(PDF) - Linear Technology
Part Name
Description
MFG CO.
'LTC1289BCSW' PDF : 28 Pages View PDF
LTC1289
TYPICAL APPLICATI S
A “Quick Look” Circuit for the LTC1289
SNEAK-A-BITTM
Users can get a quick look at the function and timing of the The LTC1289’s unique ability to software select the polar-
LTC1289 by using the following simple circuit. REF+ and ity of the differential inputs and the output word length is
DIN are tied to VCC selecting a 3V input span, CH7 as a used to achieve one more bit of resolution. Using the
single-ended input, unipolar mode, MSB-first format and circuit below with two conversions and some software, a
16-bit word length. ACLK is driven by an external clock and 2’s complement 12-bit + sign word is returned to memory
SCLK is driven by one half the clock rate. CS is driven at inside the MPU. The MC68HC05C4 was chosen as an
1/128 the clock rate by the 74HC393 and DOUT outputs the example, however, any processor that operates at 3.3V
data. All other pins are tied to a ground plane. The output could be used.
data from the DOUT pin can be viewed on an oscilloscope
which is set up to trigger on the falling edge of CS.
Two 12-bit unipolar conversions are performed: the first
over a 0V to 2.5V span and the second over a 0V to –2.5V
span (by reversing the polarity of the inputs). The sign of
A “Quick Look” Circuit for the LTC1289
the input is determined by which of the two spans con-
3.0V tained it. Then the resulting number (ranging from –4095
22µF
f
A1
VCC
to +4095 decimal) is converted to 2’s complement nota-
CLR1
A2
0.1µF tion and stored in RAM.
CHO
VCC
1QA
CLR2
CH1
ACLK
f/2
CH2
SCLK
1QB 74HC393 2QA
1QC
2QB
SNEAK-A-BIT Circuit
CH3
DIN
1QD
2QC
CH4
DOUT
LTC1289
CH5
CS
GND
2QD
22µF
+3.3V
2MHz
CH6
REF+
f/128
ACLK
VIN
CH7
REF–
COM
V–
LTC1289 TA02
CHO
VCC
1k
DGND
AGND
CLOCK IN
2MHz MAX
CH1
ACLK
OTHER CHANNELS
CH2
SCLK
MC68HC05C4
SCLK
OR SNEAK-A-BIT
INPUTS
CH3
DIN
MOSI
TO
OSCILLOSCOPE
CH4
DOUT
LTC1289
CH5
CS
MISO
CO
VIN
–2.5V TO +2.5V
CH6
CH7
REF+
REF–
10µF
LTC1289 TA03
Scope Trace of LTC1289 “Quick Look” Circuit
Showing A/D Output of 010101010101 (555HEX)
COM
DGND
V–
AGND
LT1019
–2.5
0.1µF
–3.3V
ACLK
SCLK
CS
D
OUT
DEGLITCHER
TIME
MSB
(B11)
LSB
FILLS
(B0)
ZEROES
VERTICAL: 5V/DIV
HORIZONTAL: 2µs/DIV
SNEAK-A-BIT
2.5V
VIN
(+) CH6
(–) CH7
1ST CONVERSION
0V
VIN
2.5V
1ST CONVERSION
4096 STEPS
SOFTWARE
0V
0V
(–) CH6
(+) CH7
2ND CONVERSION
–2.5V
2ND CONVERSION
4096 STEPS
–2.5V
8191 STEPS
LTC1289 TA04
SNEAK-A-BIT is a trademark of Linear Technology Corp.
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