Datasheet

MAX146/MAX147
+2.7V, Low-Power, 8-Channel,
Serial 12-Bit ADCs
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• • •
• • •
t
SDV
t
SSTRB
PD0 CLOCKED IN
t
STR
SSTRB
SCLK
CS
t
SSTRB
• • •
• • • •
•
Figure 8. External Clock Mode SSTRB Detailed Timing
External Clock
In external clock mode, the external clock not only shifts
data in and out, but it also drives the analog-to-digital
conversion steps. SSTRB pulses high for one clock
period after the last bit of the control byte. Succes-
sive-approximation bit decisions are made and appear
at DOUT on each of the next 12 SCLK falling edges
(Figure 6). SSTRB and DOUT go into a high-impedance
state when CS goes high; after the next CS falling edge,
SSTRB outputs a logic low. Figure 8 shows the SSTRB
timing in external clock mode.
The conversion must complete in some minimum time,
or droop on the sample-and-hold capacitors may
degrade conversion results. Use internal clock mode if
the serial clock frequency is less than 100kHz, or if
serial clock interruptions could cause the conversion
interval to exceed 120µs.
Internal Clock
In internal clock mode, the MAX146/MAX147 generate
their own conversion clocks internally. This frees the µP
from the burden of running the SAR conversion clock
and allows the conversion results to be read back at the
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CS
SCLK
DIN
DOUT
t
CSH
t
CSS
t
CL
t
DS
t
DH
t
DV
t
CH
t
DO
t
TR
t
CSH
Figure 7. Detailed Serial-Interface Timing