MAX110 Datasheet, PDF (15/24 Pages) Maxim Integrated Products – Low-Cost, 2-Channel, ±14-Bit Serial ADCs

Low-Cost, 2-Channel, ±14-Bit Serial ADCs
Table 1. Input Control-Word Bit Map
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0
NO-OP NU NU CONV4 CONV3 CONV2 CONV1 DV4 DV2 NU NU CHS CAL NUL PDX PD
↑
First bit clocked in.
BIT
NAME
15
NO-OP
5, 6, 13, 14
9–12
7, 8
NU
CONV1–CONV4
DV2, DV4
DESCRIPTION
If this bit is a logic high, the remaining 15 LSBs are transferred to the control register and a
new conversion begins when CS returns high. If this bit is set low, the control word is not
passed to the control register, the ADC configuration remains unchanged, and no new con-
version begins when CS returns high.
Used for test purposes only. Set these bits low.
Conversion Time Control Bits. See Table 4.
XCLK to Oversampling Cock Ratio Control Bits. See Table 5.
4
CHS
Input Channel Select. A logic high selects channel 2 (IN2+ and IN2-), while a logic low
selects channel 1 (IN1+ and IN1-). See Tables 2 and 3.
3
CAL
Gain-Calibration Bit. A logic high selects gain-calibration mode. See Table 3.
2
NUL
Internal Offset-Null Bit. A logic high selects offset-null mode. See Table 3.
1
PDX
Oscillator Power-Down. Set this bit high to power down the RC oscillator.
0
PD
Analog Power-Down. Set this bit high to power down the analog section.
NO-OP is a zero, the control word is not transferred to
the control register, the ADC’s configuration remains
unchanged, and no new conversion is initiated. This
allows specific ADCs in a “daisy chain” arrangement to
be reconfigured while leaving the remaining ADCs
unchanged. Table 1 lists the various ADC control word
functions.
Output data is shifted out of DOUT at the same time the
input control word for the next conversion is shifted in
(Figure 8).
On power-up, all internal registers reset to zero.
Therefore, when writing the first control word to the
ADC, the data simultaneously shifted out will be zeros.
The first conversion begins when CS goes high (NO-OP
= 1). The results are placed in the 16-bit I/O register for
access on the next data-transfer operation.
Power-Down Mode
Bits 0 and 1 control the ADC’s power-down mode. If bit
0 (PD) is a logic high, power is removed from all analog
circuitry except the RC oscillator. A logic high at bit 1
(PDX) removes power from the RC oscillator. If both bits
PD and PDX are a logic high, or if PD is high and
RCSEL is low, the supply currents reduce to 4µA. If an
external XCLK clock continues to run in power-down
mode, the supply current will depend on the clock rate.
When PDX is set high, the internal RC oscillator stops
shortly after CS returns high. If the next control word
written to the device has NO-OP = 1 instructing the
ADC to convert, BUSY will go low, but because the RC
oscillator is stopped, BUSY will remain low and will not
allow a new conversion to begin. To avoid this situation,
write a “dummy” control word with NO-OP = 0 and any
combination of bits 14-0 in the control word following
the control word with PDX = 0. With NO-OP = 0, bits 14-
0 are ignored and the internal state machine resets.
Next, perform a normal 3-step calibration (see Table 3).
Note that XCLK must be connected to V_DD or GND
through a resistor (suggested value is 1MΩ) when the
RC oscillator mode is selected (RCSEL = V_DD). This
resistor is not necessary if the external oscillator mode
is used, or if the internal oscillator is not shut down.
Selecting the Analog Inputs
Bit 4 (CHS) controls which of the two differential inputs
connect to the internal ADC inputs (see the Functional
Diagram). A logic high selects IN2+ and IN2- while a
logic low selects IN1+ and IN1-. Table 2 shows the
allowable input multiplexer configurations.
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