MAX148 Datasheet, PDF (10/24 Pages) Maxim Integrated Products – +2.7V to +5.25V, Low-Power, 8-Channel, Serial 10-Bit ADCs

+2.7V to +5.25V, Low-Power, 8-Channel,
Serial 10-Bit ADCs
Table 1. Control-Byte Format
BIT 7
(MSB)
BIT 6
BIT 5
START
SEL2
SEL1
BIT 4
SEL0
BIT 3
UNI/BIP
BIT 2
SGL/DIF
BIT 1
PD1
BIT 0
(LSB)
PD0
BIT
7(MSB)
6
5
4
3
NAME
START
SEL2
SEL1
SEL0
UNI/BIP
2
SGL/DIF
1
PD1
0(LSB)
PD0
DESCRIPTION
The first logic “1” bit after CS goes low defines the beginning of the control byte.
These three bits select which of the eight channels are used for the conversion (Tables 2 and 3).
1 = unipolar, 0 = bipolar. Selects unipolar or bipolar conversion mode. In unipolar mode, an
analog input signal from 0V to VREF can be converted; in bipolar mode, the signal can range
from -VREF/2 to +VREF/2.
1 = single ended, 0 = differential. Selects single-ended or differential conversions. In single-
ended mode, input signal voltages are referred to COM. In differential mode, the voltage
difference between two channels is measured (Tables 2 and 3).
Selects clock and power-down modes.
PD1
PD0
Mode
0
0
Full power-down
0
1
Fast power-down (MAX149 only)
1
0
Internal clock mode
1
1
External clock mode
Table 2. Channel Selection in Single-Ended Mode (SGL/DIF = 1)
SEL2
0
1
0
1
0
1
0
1
SEL1
0
0
0
0
1
1
1
1
SEL0
0
0
1
1
0
0
1
1
CH0
+
CH1
+
CH2
+
CH3
CH4
+
+
CH5
+
CH6
+
CH7
+
COM
–
–
–
–
–
–
–
–
How to Start a Conversion
Start a conversion by clocking a control byte into DIN.
With CS low, each rising edge on SCLK clocks a bit from
DIN into the MAX148/MAX149’s internal shift register.
After CS falls, the first arriving logic “1” bit defines the
control byte’s MSB. Until this first “start” bit arrives, any
number of logic “0” bits can be clocked into DIN with no
effect. Table 1 shows the control-byte format.
The MAX148/MAX149 are compatible with SPI/
QSPI and MICROWIRE devices. For SPI, select the cor-
rect clock polarity and sampling edge in the SPI control
registers: set CPOL = 0 and CPHA = 0. MICROWIRE,
SPI, and QSPI all transmit a byte and receive a byte at
the same time. Using the Typical Operating Circuit, the
simplest software interface requires only three 8-bit
transfers to perform a conversion (one 8-bit transfer to
configure the ADC, and two more 8-bit transfers to clock
out the conversion result). See Figure 20 for MAX148/
MAX149 QSPI connections.
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