ADC12L030CIWM National Semiconductor, ADC12L030CIWM Datasheet - Page 3

• Manufacturer Part Number: ADC12L030CIWM
• Description: 3.3V Self-Calibrating 12-Bit Plus Sign Serial I/O A/D Converters with MUX and Sample/Hold
• Manufacturer: National Semiconductor

Pin Descriptions
CCLK
SCLK
DI
DO
EOC
CS
The clock applied to this input controls the su-
cessive approximation conversion time interval
and the acquisition time. The rise and fall times
of the clock edges should not exceed 1 µs.
This is the serial data clock input. The clock
applied to this input controls the rate at which
the serial data exchange occurs. The rising
edge loads the information on the DI pin into
the multiplexer address and mode select shift
register. This address controls which channel
of the analog input multiplexer (MUX) is se-
lected and the mode of operation for the A/D.
With CS low the falling edge of SCLK shifts the
data resulting from the previous ADC conver-
sion out on DO, with the exception of the first
bit of data. When CS is low continuously, the
first bit of the data is clocked out on the rising
edge of EOC (end of conversion). When CS is
toggled the falling edge of CS always clocks
out the first bit of data. CS should be brought
low when SCLK is low. The rise and fall times
of the clock edges should not exceed 1 µs.
This is the serial data input pin. The data ap-
plied to this pin is shifted by the rising edge of
SCLK into the multiplexer address and mode
select register. Tables 2, 3, 4, 5 show the as-
signment of the multiplexer address and the
mode select data.
The data output pin. This pin is an active push/
pull output when CS is Low. When CS is High
this output is in TRI-STATE. The A/D conver-
sion result (D0–D12) and converter status data
are clocked out by the falling edge of SCLK on
this pin. The word length and format of this re-
sult can vary (see Table 1 ). The word length
and format are controlled by the data shifted
into the multiplexer address and mode select
register (see Table 5 ).
This pin is an active push/pull output and indi-
cates the status of the ADC12L030/2/4/8.
When low, it signals that the A/D is busy with a
conversion,
power down cycle. The rising edge of EOC sig-
nals the end of one of these cycles.
This is the chip select pin. When a logic low is
applied to this pin, the rising edge of SCLK
shifts the data on DI into the address register.
This low also brings DO out of TRI-STATE.
With CS low the falling edge of SCLK shifts the
data resulting from the previous ADC conver-
sion out on DO, with the exception of the first
bit of data. When CS is low continuously, the
first bit of the data is clocked out on the rising
edge of EOC (end of conversion). When CS is
toggled the falling edge of CS always clocks
out the first bit of data. CS should be brought
low when SCLK is low. The falling edge of CS
resets a conversion in progress and starts the
sequence for a new conversion. When CS is
brought back low during a conversion, that
conversion is prematurely ended. The data in
the output latches may be corrupted. There-
fore, when CS is brought back low during a
conversion in progress the data output at that
auto-calibration,
auto-zero
or
3
DOR
CONV
PD
CH0–CH7
COM
MUXOUT1,
MUXOUT2
A/DIN1,
A/DIN2
V
REF
+
time should be ignored. CS may also be left
continuously low. In this case it is imperative
that the correct number of SCLK pulses be ap-
plied to the ADC in order to remain synchro-
nous. After the ADC supply power is applied, it
expects to see 13 clock pulses for each I/O se-
quence. The number of clock pulses the ADC
expects is the same as the digital output word
length. This word length can be modified by
the data shifted in on the DO pin. Table 5 de-
tails the data required.
This is the data output ready pin. This pin is an
active push/pull output. It is low when the con-
version result is being shifted out and goes
high to signal that all the data has been shifted
out.
A logic low is required on this pin to program
any mode or change the ADC’s configuration
as listed in the Mode Programming Table
( Table 5 ) such as 12-bit conversion, 8-bit con-
version, Auto Cal, Auto Zero etc. When this pin
is high the ADC is placed in the read data only
mode. While in the read data only mode, bring-
ing CS low and pulsing SCLK will only clock
out on DO any data stored in the ADCs output
shift register. The data on DI will be neglected.
A new conversion will not be started and the
ADC will remain in the mode and/or configura-
tion previously programmed. Read data only
cannot be performed while a conversion,
Auto-Cal or Auto-Zero are in progress.
This is the power down pin. When PD is high
the A/D is powered down; when PD is low the
A/D is powered up. The A/D takes a maximum
of 700 µs to power up after the command is
given.
These are the analog inputs of the MUX. A
channel input is selected by the address infor-
mation at the DI pin, which is loaded on the ris-
ing edge of SCLK into the address register
(see Tables 2, 3, 4 ).
The voltage applied to these inputs should not
exceed V
range on an unselected channel will corrupt
the reading of a selected channel.
This pin is another analog input pin. It is used
as a pseudo ground when the analog multi-
plexer is single-ended.
These
pins.
These are the converter input pins. MUXOUT1
is usually tied to A/DIN1. MUXOUT2 is usually
tied to A/DIN2. If external circuitry is placed be-
tween MUXOUT1 and A/DIN1, or MUXOUT2
and A/DIN2 it may be necessary to protect
these pins. The voltage at these pins should
not exceed V
5 ).
This is the positive analog voltage reference
input. In order to maintain accuracy the voltage
range of V
A
are
+ or go below GND. Exceeding this
REF
A
+
or go below AGND (see Figure
(V
the
REF
= V
multiplexer
REF
+ − V
www.national.com
REF
output
−) is