ML2281, ML2282, ML2284, ML2288
SINGLE-ENDED MUX MODE
M
UX ADDRESS
SGL/DIF
1
1
ODD/SIGN
0
1
0
+
+
CHANNEL#
1
DIGITAL INTERFACE
The block diagram and timing diagrams in Figures 2-5
illustrate how a conversion sequence is performed.
A conversion is initiated when
CS
is pulsed low. This line
must me held low for the entire conversion. The converter is
now waiting for a start bit and its MUX assignment word.
A clock is applied to the CLK input. On each rising edge
of the clock, the data on DI is clocked into the MUX
address shift register. The start bit is the first logic “1” that
appears on the DI input (all leading edge zeros are
ignored). After the start bit, the device clocks in the next 2
to 4 bits for the MUX assignment word.
When the start bit has been shifted into the start location
of the MUX register, the input channel has been assigned
and a conversion is about to begin. An interval of 1/2
clock period is used for sample & hold settling through the
selected MUX channels. The SAR status output goes high
at this time to signal that a conversion is now in progress
and the DI input is ignored.
The DO output comes out of High impedance and
provides a leading zero for this one clock period.
When the conversion begins, the output of the
comparator, which indicates whether the analog input is
greater than or less than each successive voltage from the
internal DAC, appears at the DO output on each falling
edge of the clock. This data is the result of the conversion
being shifted out (with MSB coming first) and can be read
by external logic or µP immediately.
After 8 clock periods, the conversion is completed. The SAR
status line returns low to indicate this 1/2 clock cycle later.
The serial data is always shifted out MSB first during the
conversion. After the conversion has been completed, the
data can be shifted out a second time with LSB first,
depending on level of
SE
input. For the case of ML2288, if
SE
= 1, the data is shifted out MSB first during the
conversion only. If
SE
is brought low before the end of
conversion (which is signalled by the high to low transition
of SARS), the data is shifted out again immediately after the
end of conversion; this time LSB first. If
SE
is brought low
after end of conversion, the LSB first data is shifted out on
falling edges of clock after
SE
goes low. For ML2282 and
2284,
SE
is internally tied low, so data is shifted out MSB
first, then shifted out a second time LSB first at end of
conversion. For ML2281,
SE
is internally tied high, so data is
shifted out only once MSB first.
All internal registers are cleared when the
CS
input is
high. If another conversion is desired,
CS
must make a
high to low transition followed by address information.
The DI input and DO output can be tied together and
controlled through a bidirectional µP I/O bit with one
connection. This is possible because the DI input is only
latched in during the MUX addressing interval while the
DO output is still in the high impedance state.
DIFFERENTIAL MUX MODE
M
UX ADDRESS
SGL/DIF
0
0
ODD/SIGN
0
1
0
+
–
CHANNEL#
1
–
+
Table 3. ML2282 MUX Addressing 2 Single-Ended
or 1 Differential Channel
8 Single-Ended
0
1
2
3
4
5
6
7
+
+
+
+
+
+
+
+
COM (–)
V
BIAS
8 Pseudo-Differential
0
1
2
3
4
5
6
7
+
+
+
+
+
+
+
+
+
COM (–)
4 Differential
0, 1
+ (–)
– (+)
2, 3
+ (–)
– (+)
4, 5
+ (–)
– (+)
6, 7
+ (–)
– (+)
+
V
BIAS
2, 3
4
5
6
7
0, 1
Mixed Mode
+
–
–
+
+
+
+
+
COM (–)
Figure 7. Analog Input Multiplexer Functional
Options for ML2288
13
MICRO-LINEAR [ MICRO LINEAR CORPORATION ]
