MAX1241BESA Maxim, MAX1241BESA Datasheet - Page 10

• Manufacturer Part Number: MAX1241BESA
• Description: +2.7V / Low-Power / 12-Bit Serial ADCs in 8-Pin SO
• Manufacturer: Maxim

+2.7V, Low-Power,
12-Bit Serial ADCs in 8-Pin SO
ed. After an internally timed conversion period, the end
of conversion is signaled by DOUT pulling high. Data
can then be shifted out serially with the external clock.
Power consumption can be reduced significantly by
shutting down the MAX1240/MAX1241 between con-
versions. Figure 6 shows a plot of average supply cur-
rent versus conversion rate. Because the MAX1241
uses an external reference voltage (assumed to be pre-
sent continuously), it “wakes up” from shutdown more
quickly (in 4µs) and therefore provides lower average
supply currents. The wake-up time (t
from when SHDN is deasserted to the time when a con-
version may be initiated (Figure 5). For the MAX1240,
this time depends on the time in shutdown (Figure 7)
because the external 4.7µF reference bypass capacitor
loses charge slowly during shutdown.
The actual conversion does not require the external
clock. This allows the conversion result to be read back
at the µP’s convenience at any clock rate from up to
2.1MHz. The clock duty cycle is unrestricted if each
clock phase is at least 200ns. Do not run the clock
while a conversion is in progress.
Conversion-start and data-read operations are controlled
by the CS and SCLK digital inputs. The timing diagrams
of Figures 8 and 9 outline serial-interface operation.
A CS falling edge initiates a conversion sequence: the
T/H stage holds the input voltage, the ADC begins to
convert, and DOUT changes from high impedance to
logic low. SCLK must be kept low during the conver-
sion. An internal register stores the data when the con-
version is in progress.
10
Figure 8. Interface Timing Sequence
______________________________________________________________________________________
TRACK/HOLD
STATE
DOUT
INTERFACE IDLE
CYCLE TIME
SCLK
Using
CS
TRACK
SHDN to Reduce Supply Current
CONVERSION
IN PROGRESS
7.5 s (t
HOLD
CONV
)
Timing and Control
EOC
0 s
External Clock
EOC
WAKE
1
) is the time
B11 B10 B9
4
B8
CLOCK OUT SERIAL DATA
12.5 0.476 s = 5.95 s
TOTAL = 13.7 s
B7
B6
Figure 6. Average Supply Current vs. Conversion Rate
Figure 7. Typical Reference Power-Up Delay vs. Time in
Shutdown
B5
8
TRACK
B4
B3
0.001
0.01
0.8
0.6
0.4
0.2
0.0
1.0
0.1
10
B2
1
0.001
0.1
B1
V
R
CODE = 010101010000
12
DD =
LOAD
1
B0
V
= , C
0.01
REF
TIME IN SHUTDOWN (sec)
CONVERSION RATE (Hz)
= 3.0V
10
MAX1240
LOAD
TRAILING
ZEROS
0 s
= 50pF
100
0.1
16
MAX1241
1k
1
0.24 s
(t
10k
CS
IDLE
)
100k
10
HOLD