LTC1273ACS Ver la hoja de datos (PDF) - Linear Technology
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LTC1273ACS Datasheet PDF : 24 Pages
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LTC1273
LTC1275/LTC1276
APPLICATI S I FOR ATIO
This is a two byte read instruction which loads the ADC
data (address B000) into the HL register pair. During the
first read operation, BUSY forces the microprocessor to
WAIT for the LTC1273 conversion. No WAIT states are
inserted during the second read operation when the mi-
croprocessor is reading the high data byte.
TMS32010 Microcomputer
Figure 20 shows an LTC1273/TMS32010 interface. The
LTC1273 is operating in the ROM Mode.
The LTC1273 is mapped at a port address. The following
I/O instruction starts a conversion and reads the previous
conversion result into data memory.
IN A,PA
(PA = PORT ADDRESS)
When conversion is complete, a second I/O instruction
reads the up-to-date data into memory and starts another
conversion. A delay at least as long as the ADC conversion
time must be allowed between I/O instructions.
PA2
PA0
DEN
TMS32010
PORT ADDRESS BUS
EN
ADDRESS
DECODE
LTC1273/75/76
CS
current so it can be accurately driven by the unbuffered
MUX. The CD4520 counter increments the MUX channel
after each sample is taken. Figure 22 shows the acquisi-
tion time of LTC1275 vs the source resistance. For a
500Ω maximum “on” resistance of the CD4051, the
acquisition time of the ADC is not greatly affected. For
larger source resistances, modest increases in acquisi-
tion time must be allowed.
5V
CD4051
VDD
8 INPUT
CHANNELS
± 2.8V
INPUT
VARIES
NO
BUFFER
REQUIRED
D11
AIN
•
•
•
D0
LTC1275
CS
RD
BUSY
VSS
VEE A B C
– 5V
5V
Q2 ENABLE
Q1
CD4520
COUNTER
Q0 RESET
µP
OR
DSP
LTC1273/75/76 • F21
Figure 21. MUXing the LTC1275 with CD4051
RD
D11
D11
DATA BUS
D0
D0/8 HBEN
LINEAR CIRCUITRY OMITTED FOR CLARITY
LTC1273/75/76 • F20
Figure 20. TMS32010 Interface
4
3
RSOURCE
AIN LTC1275
VIN
2
MUXing with CD4051
The high input impedance of the LTC1273/LTC1275/
LTC1276 provides an easy, cheap, fast, and accurate way
to multiplex many channels of data through one con-
verter. Figure 21 shows a low cost CD4051 connected to
the LTC1275. The LTC1275’s input draws no DC input
1
500Ω
0
10
100
1k
10k
SOURCE RESISTANCE (Ω)
LTC1273/75/76 • F22
Figure 22. Acqusition Time of LTC1275 vs Source Resistance
20
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