mc145053p Lansdale Semiconductor, Inc., mc145053p Datasheet - Page 11

• Manufacturer Part Number: mc145053p
• Description: 10-bit A/d Converter With Serial Interface Cmos
• Manufacturer: Lansdale Semiconductor, Inc.

ML145053
Legacy Applications Information
DESCRIPTION
four analog signals to a microprocessor.
effective means to simplify this type of circuit design. Utilizing
one ADC, four analog inputs are interfaced to a CMOS or
NMOS microprocessor with a serial peripheral interface (SPI)
port. Processors with National Semiconductor's MICROWIRE
serial port may also be used. Full duplex operation optimizes
throughput for this system.
DIGITAL DESIGN CONSIDERATIONS
reduce power supply size and cost. The NMOS MCUs may be
used if power consumption is not critical. A V DD or V SS 0.1
µF bypass capacitor should be closely mounted to the ADC.
output pin 1 to define when data is ready.
ANALOG DESIGN CONSIDERATIONS
1 kΩ may be directly interfaced to the ADC, eliminating the
need for buffer amplifiers. Separate lines connect the V ref and
V AG pins on the ADC with the controllers to provide isolation
from system noise.
put lines may need to be shielded, depending on their length
and electrical environment. This should be verified during pro-
totyping with an oscilloscope. If shielding is required, a twist-
ed pair or foil-shielded wire (not coax) is appropriate for this
low frequency application. One wire of the pair or the shield
must be V AG .
Page 11 of 15
This example application of the ML145053 ADC interfaces
Figure 15 illustrates how the ML145053 is used as a cost
Motorola's MC68HC05C4 CMOS MCU may be chosen to
The ML145053 has the end-of-conversion (EOC) signal at
Analog signal sources with output impedances of less than
Although not indicated in Figure 15, the V ref and sensor out-
www.lansdale.com
tion shown in Figure 15. However, the reference circuitry may
be simplified by tying VAG to system ground and V ref to the
system's positive supply. (See Figure 16.)
and V AG pins is recommended. These pins are adjacent on the
ADC package which facilitates mounting the capacitor very
close to the ADC.
SOFTWARE CONSIDERATIONS
four analog inputs, AN0 through AN3, are scanned by reading
the analog value of the previously addressed channel into the
MCU and sending the address of the next channel to be read to
the ADC, simultaneously.
version signal (at pin 1) to define the conversion interval. EOC
may be used to generate an interrupt, which is serviced by
reading the serial data from the ADC. The software flow
should then process and format the data.
are two types of offsets involved. In the first type of offset, the
channel information sent to the ADCs is offset by 12 bits. That
is, in the 16-bit stream, only the first 4 bits (4 MSBs) contain
the channel information. The balance of the bits are don't
cares. This results in 3 don't-care nibbles, as shown in Table 2.
The second type of offset is in the conversion result returned
from the ADC; this is offset by 6 bits. In the 16-bitstream, the
first 10 bits (10 MSBs) contain the conversion result. The last
6 bits are zeroes. The hexadecimal result is shown in the first
column of Table 3. The second column shows the result after
the offset is removed by a micro-processor routine. If the 16-
bit format is used, the ADC can transfer one continuous 16-bit
stream or two intermittent 8-bitstreams.
A reference circuit voltage of 5 volts is used for the applica-
A bypass capacitor of approximately 0.22 µF across theV ref
The software flow for acquisition is straight forward. The
The designer utilizing the ML145053 has the end-of-con-
When this ADC is used with a 16-bit (2-byte) transfer, there
LANSDALE Semiconductor, Inc.
Issue A