Datasheet

+2.7V to +5.25V, Low-Power, 8-Channel,
Serial 10-Bit ADCs
MAX148/MAX149
10
Table 1. Control-Byte Format
Table 2. Channel Selection in Single-Ended Mode (SGL/DIF = 1)
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 correct 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.
BIT 7
(MSB)
BIT 6 BIT 5 BIT 4 BIT 3 BIT 2 BIT 1
BIT 0
(LSB)
START SEL2 SEL1 SEL0 UNI/BIP SGL//DIF PD1 PD0
BIT NAME DESCRIPTION
7(MSB) START The first logic “1” bit after CS goes low defines the beginning of the control byte.
6
5
4
SEL2
SEL1
SEL0
These three bits select which of the eight channels are used for the conversion (Tables 2 and 3)
3 UNI/BIP
1 = unipolar, 0 = bipolar. Selects unipolar or bipolar conversion mode. In unipolar mode, an
analog input signal from 0 to V
REF
can be converted; in bipolar mode, the signal can range from
-V
REF
/2 to +V
REF
/2.
2 SGL/DIF
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).
1 PD1 Selects clock and power-down modes.
0(LSB) PD0
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
SEL2 SEL1 SEL0 CH0 CH1 CH2 CH3 CH4 CH5 CH6 CH7 COM
0 0 0
+ -
1 0 0
+ -
0 0 1
+ -
1 0 1
+ -
0 1 0
+ -
1 1 0
+ -
0 1 1
+ -
1 1 1
+ -