MAX1403EAI ,+3V / 18-Bit / Low-Power / Multichannel / Oversampling Sigma-Delta ADCApplicationsCS 3 26 DOUTPortable Industrial InstrumentsRESET 4 25 INTPortable Weigh ScalesDS1 5 24 ..
MAX1403EAI+ ,+3V, 18-Bit, Low-Power, Multichannel, Oversampling (Sigma-Delta) ADCELECTRICAL CHARACTERISTICS(V+ = +2.7V to +3.6V, V = +2.7V to +3.6V, V = +1.25V, REFIN- = AGND, f = ..
MAX1406CAE ,15kV ESD-Protected / EMC-Compliant / 230kbps / 3-Tx/3-Rx RS-232 ICFeaturesThe MAX1406 is an RS-232 IC designed to meet the ' Enhanced ESD Protection:stringent electr ..
MAX1406CPE ,15kV ESD-Protected / EMC-Compliant / 230kbps / 3-Tx/3-Rx RS-232 ICGeneral Description ________
MAX1406CWE ,15kV ESD-Protected / EMC-Compliant / 230kbps / 3-Tx/3-Rx RS-232 ICELECTRICAL CHARACTERISTICS(V = +4.5V to +5.5V, V = +10.8V to +13.2V, V = -10.8V to -13.2V, T = T to ..
MAX1406CWE ,15kV ESD-Protected / EMC-Compliant / 230kbps / 3-Tx/3-Rx RS-232 ICELECTRICAL CHARACTERISTICS(V = +4.5V to +5.5V, V = +10.8V to +13.2V, V = -10.8V to -13.2V, T = T to ..
MAX4020ESD ,Low-Cost / High-Speed / SOT23 / Single-Supply Op Amps with Rail-to-Rail OutputsFeaturesThe MAX4012 single, MAX4016 dual, MAX4018 triple,' Low-Costand MAX4020 quad op amps are uni ..
MAX4020ESD+T ,Low-Cost, High-Speed, Single-Supply Op Amps with Rail-to-Rail OutputsFeaturesThe MAX4012 single, MAX4016 dual, MAX4018 triple,♦ Low-Costand MAX4020 quad op amps are uni ..
MAX4022EEE ,Low-Cost / High-Speed / Single-Supply / Gain of +2 Buffers with Rail-to-Rail Outputs in SOT23Applications__________Typical Operating CircuitPortable/Battery-Powered InstrumentsVideo Line Drive ..
MAX4023EEE ,Triple and Quad / 2:1 Video Multiplexer- Amplifiers with Fixed and Settable GainELECTRICAL CHARACTERISTICS—Dual Supply(V = +5V, V = -5V, R = ∞, EN = +5V, V = REF = OUT_ = 0V, T = ..
MAX4023EEE+ ,Triple and Quad, 2:1 Video Multiplexer-Amplifiers with Fixed and Settable Gainapplications withMAX4025EUP -40°C to +85°C 20 TSSOPdifferential gain and phase errors of 0.07% and ..
MAX4024ESD+T ,Triple and Quad, 2:1 Video Multiplexer-Amplifiers with Fixed and Settable GainMAX4023–MAX402619-2758; Rev 1; 11/09Triple and Quad, 2:1 Video Multiplexer-Amplifiers with Fixed an ..
MAX1403CAI-MAX1403EAI
+3V / 18-Bit / Low-Power / Multichannel / Oversampling Sigma-Delta ADC
General DescriptionThe MAX1403 18-bit, low-power, multichannel, serial-
output analog-to-digital converter (ADC) features
matched 200µA current sources for sensor excitation.
This ADC uses a sigma-delta modulator with a digital
decimation filter to achieve 16-bit accuracy. The digital
filter’s user-selectable decimation factor allows the con-
version resolution to be reduced in exchange for a
higher output data rate. True 16-bit performance is
achieved at an output data rate of up to 480sps. In
addition, the modulator sampling frequency may be
optimized for either lowest power dissipation or highest
throughput rate. The MAX1403 operates from +3V.
This device offers three fully differential input channels
that may be independently programmed with a gain
between +1V/V and +128V/V. Furthermore, it can com-
pensate an input-referred DC offset up to 117% of the
selected full-scale range. These three differential chan-
nels may also be configured to operate as five pseudo-
differential input channels. Two additional, fully
differential system-calibration channels are provided for
gain and offset error correction.
The MAX1403 can be configured to sequentially scan all
signal inputs and provide the results via the serial inter-
face with minimum communications overhead. When
used with a 2.4576MHz or 1.024MHz master clock, the
digital decimation filter can be programmed to produce
zeros in its frequency response at the line frequency and
associated harmonics, ensuring excellent line rejection
without the need for further postfiltering.
The MAX1403 is available in a 28-pin SSOP package.
ApplicationsPortable Industrial Instruments
Portable Weigh Scales
Loop-Powered Systems
Pressure Transducers
Features18-Bit Resolution, Sigma-Delta ADC16-Bit Accuracy with No Missing Codes to 480spsMatched On-Board Current Sources (200µA) for
Sensor ExcitationLow Quiescent Current
250µA (operating mode)
2µA (power-down mode)3 Fully Differential or 5 Pseudo-Differential Signal
Input Channels2 Additional, Fully Differential Calibration
Channels/Auxiliary Input ChannelsProgrammable Gain and OffsetFully Differential Reference InputsConverts Continuously or On CommandAutomatic Channel Scanning and Continuous
Data Output ModeOperates with Analog and Digital Supplies
from +2.7V to +3.6VSPI™/QSPI™-Compatible 3-Wire Serial Interface28-Pin SSOP Package
MAX1403, 18-Bit, Low-Power, Multichannel,
Oversampling (Sigma-Delta) ADC
Pin Configuration
Ordering InformationSPI and QSPI are trademarks of Motorola, Inc.
MAX1403
+3V, 18-Bit, Low-Power, Multichannel,
Oversampling (Sigma-Delta) ADC
ABSOLUTE MAXIMUM RATINGS
ELECTRICAL CHARACTERISTICS(V+ = +2.7V to +3.6V, VDD= +2.7V to +3.6V, VREFIN+= +1.25V, REFIN- = AGND, fCLKIN= 2.4576MHz, TA= TMINto TMAX, unless
otherwise noted. Typical values are at TA= +25°C.)
Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional
operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to
absolute maximum rating conditions for extended periods may affect device reliability.
V+ to AGND, DGND.................................................-0.3V to +6V
VDDto AGND, DGND...............................................-0.3V to +6V
AGND to DGND.....................................................-0.3V to +0.3V
Analog Inputs to AGND................................-0.3V to (V+ + 0.3V)
Analog Outputs to AGND.............................-0.3V to (V+ + 0.3V)
Reference Inputs to AGND...........................-0.3V to (V+ + 0.3V)
CLKIN and CLKOUT to DGND...................-0.3V to (VDD+ 0.3V)
All Other Digital Inputs to DGND..............................-0.3V to +6V
All Digital Outputs to DGND.......................-0.3V to (VDD+ 0.3V)
Maximum Current Input into Any Pin..................................50mA
Continuous Power Dissipation (TA= +70°C)
28-Pin SSOP (derate 9.52mW/°C above +70°C)........524mW
Operating Temperature Ranges
MAX1403CAI.....................................................0°C to +70°C
MAX1403EAI...................................................-40°C to +85°C
Storage Temperature Range.............................-60°C to +150°C
Lead Temperature (soldering, 10sec).............................+300°C
MAX1403
+3V, 18-Bit, Low-Power, Multichannel,
Oversampling (Sigma-Delta) ADC
ELECTRICAL CHARACTERISTICS (continued)(V+ = +2.7V to +3.6V, VDD= +2.7V to +3.6V, VREFIN+= +1.25V, REFIN- = AGND, fCLKIN= 2.4576MHz, TA= TMINto TMAX, unless
otherwise noted. Typical values are at TA= +25°C.)
+3V, 18-Bit, Low-Power, Multichannel,
Oversampling (Sigma-Delta) ADC
ELECTRICAL CHARACTERISTICS (continued)(V+ = +2.7V to +3.6V, VDD= +2.7V to +3.6V, VREFIN+= +1.25V, REFIN- = AGND, fCLKIN= 2.4576MHz, TA= TMINto TMAX, unless
otherwise noted. Typical values are at TA= +25°C.)
MAX1403
MAX1403
+3V, 18-Bit, Low-Power, Multichannel,
Oversampling (Sigma-Delta) ADC
ELECTRICAL CHARACTERISTICS (continued)(V+ = +2.7V to +3.6V, VDD= +2.7V to +3.6V, VREFIN+= +1.25V, REFIN- = AGND, fCLKIN= 2.4576MHz, TA= TMINto TMAX, unless
otherwise noted. Typical values are at TA= +25°C.)
MAX1403
+3V, 18-Bit, Low-Power, Multichannel,
Oversampling (Sigma-Delta) ADC
Note 1:Contact factory for INL limits applicable with FS1 = 0 and MF1, MF0 = 1, 2, or 3.
Note 2:Nominal gain is 0.98. This ensures a full-scale input voltage may be applied to the part under all conditions without caus-
ing saturation of the digital output data.
Note 3:Positive Full-Scale Error includes zero-scale errors (unipolar offset error or bipolar zero error) and applies to both unipolar
and bipolar input ranges. This error does not include the nominal gain of 0.98.
Note 4:Full-Scale Drift includes zero-scale drift (unipolar offset drift or bipolar zero drift) and applies to both unipolar and bipolar
input ranges.
Note 5:Gain Error does not include zero-scale errors. It is calculated as (full-scale error - unipolar offset error) for unipolar ranges
and as (full-scale error - bipolar zero error) for bipolar ranges. This error does not include the nominal gain of 0.98.
Note 6:Gain-Error Drift does not include unipolar offset drift or bipolar zero drift. It is effectively the drift of the part if zero-scale
error is removed.
Note 7:Use of the offset DAC does not imply that any input may be taken below AGND.
Note 8:Additional noise added by the offset DAC is dependent on the filter cutoff, gain, and DAC setting. No noise is added for a
DAC code of 0000.
Note 9:Guaranteed by design or characterization; not production tested.
Note 10:The absolute input voltage must be within the input voltage range specification.
Note 11:All AIN and REFIN pins have identical input structures. Leakage is production tested only for the AIN3, AIN4, AIN5,
CALGAIN, and CALOFF inputs.
Note 12:The dynamic load presented by the MAX1403 analog inputs for each gain setting is discussed in detail in the Switching
Network section.Values are provided for the maximum allowable external series resistance.
Note 13:The input voltage range for the analog inputs is with respect to the voltage on the negative input of its respective differen-
tial or pseudo-differential pair. Table 5 shows which inputs form differential pairs.
Note 14:VREF= VREFIN+- VREFIN-.
Note 15:These specifications apply to CLKOUT only when driving a single CMOS load.
ELECTRICAL CHARACTERISTICS (continued)(V+ = +2.7V to +3.6V, VDD= +2.7V to +3.6V, VREFIN+= +1.25V, REFIN- = AGND, fCLKIN= 2.4576MHz, TA= TMINto TMAX, unless
otherwise noted. Typical values are at TA= +25°C.)
MAX1403
+3V, 18-Bit, Low-Power, Multichannel,
Oversampling (Sigma-Delta) ADC
TIMING CHARACTERISTICS(V+ = +2.7V to +3.6V, VDD= +2.7V to +3.6V, AGND = DGND, fCLKIN= 2.4576MHz, input logic 0 = 0V, logic 1 = VDD, TA= TMINto
TMAX, unless otherwise noted.) (Notes 20, 21, 22)
Note 16:The burn-out currents require a 500mV overhead between the analog input voltage and both V+ and AGND to operate
correctly.
Note 17:Measured at DC in the selected passband. PSR at 50Hz will exceed 120dB with filter notches of 25Hz or 50Hz and FAST
bit = 0. PSR at 60Hz will exceed 120dB with filter notches of 20Hz or 60Hz and FAST bit = 0.
Note 18:PSR depends on gain. For a gain of +1V/V, PSR is 70dB typical. For a gain of +2V/V, PSR is 75dB typical. For a gain of
+4V/V, PSR is 80dB typical. For gains of +8V/V to +128V/V, PSR is 85dB typical.
Note 19:Standby power-dissipation and current specifications are valid only with CLKIN driven by an external clock and with the
external clock stopped. If the clock continues to run in standby mode, the power dissipation will be considerably higher.
When used with a resonator or crystal between CLKIN and CLKOUT, the actual power dissipation and IDDin standby
mode will depend on the resonator or crystal type.
MAX1403
+3V, 18-Bit, Low-Power, Multichannel,
Oversampling (Sigma-Delta) ADC
Note 20:All input signals are specified with tr= tf= 5ns (10% to 90% of VDD) and timed from a voltage level of 1.6V.
Note 21:See Figure 4.
Note 22:Timings shown in tables are for the case where SCLK idles high between accesses. The part may also be used with SCLK
idling low between accesses, provided CSis toggled. In this case SCLK in the timing diagrams should be inverted and
the terms “SCLK Falling Edge” and “SCLK Rising Edge” exchanged in the specification tables. If CSis permanently tied
low, the part should only be operated with SCLK idling high between accesses.
Note 23:CLKIN duty cycle range is 45% to 55%. CLKIN must be supplied whenever the MAX1403 is not in standby mode. If no
clock is present, the device can draw higher current than specified.
Note 24:The MAX1403 is production tested with fCLKINat 2.5MHz (1MHz for some IDDtests).
Note 25:Measured with the load circuit of Figure 1 and defined as the time required for the output to cross the VOLor VOHlimits.
Note 26:For read operations, SCLK active edge is falling edge of SCLK.
Note 27:Derived from the time taken by the data output to change 0.5V when loaded with the circuit of Figure 1. The number is
then extrapolated back to remove effects of charging or discharging the 50pF capacitor. This ensures that the times quot-
ed in the timing characteristics are true bus-relinquish times and are independent of external bus loading capacitances.
Note 28:INTreturns high after the first read after an output update. The same data can be read again while INTis high, but be
careful not to allow subsequent reads to occur close to the next output update.
Note 29:Auxiliary inputs DS0 and DS1 are latched on the first falling edge of SCLK during a data-read cycle.
TIMING CHARACTERISTICS (continued)(V+ = +2.7V to +3.6V, VDD= +2.7V to +3.6V, AGND = DGND, fCLKIN= 2.4576MHz, input logic 0 = 0V, logic 1 = VDD, TA= TMINto
TMAX, unless otherwise noted.) (Notes 20, 21, 22)
Figure 1. Load Circuit for Bus-Relinquish Time and VOLand
MAX1403
+3V, 18-Bit, Low-Power, Multichannel,
Oversampling (Sigma-Delta) ADC
Typical Operating Characteristics(V+ = +3V, VDD= +3V, VREFIN+= +1.25V, REFIN- = AGND, fCLKIN= 2.4576MHz, transducer excitation currents disabled, TA=
+25°C, unless otherwise noted.)
MAX1403
+3V, 18-Bit, Low-Power, Multichannel,
Oversampling (Sigma-Delta) ADC
Typical Operating Characteristics (continued)(V+ = +3V, VDD= +3V, VREFIN+= +1.25V, REFIN- = AGND, fCLKIN= 2.4576MHz, transducer excitation currents disabled, TA=
+25°C, unless otherwise noted.)
Note 30:Minimize capacitive loading at CLKOUT for lowest VDDsupply current. Typical Operating Characteristicsshow VDD
supply current with CLKOUT loaded by 120pF.
MAX1403
+3V, 18-Bit, Low-Power, Multichannel,
Oversampling (Sigma-Delta) ADC
Pin Description
MAX1403
+3V, 18-Bit, Low-Power, Multichannel,
Oversampling (Sigma-Delta) ADC
Pin Description (continued)
MAX1403
+3V, 18-Bit, Low-Power, Multichannel,
Oversampling (Sigma-Delta) ADC
_______________Detailed Description
Circuit DescriptionThe MAX1403 is a low-power, multichannel, serial-output,
sigma-delta ADC designed for applications with a wide
dynamic range, such as weigh scales and pressure
transducers. The functional block diagram in Figure 2
contains a switching network, a modulator, a PGA, two
buffers, an oscillator, an on-chip digital filter, two
matched transducer excitation current sources, and a
bidirectional serial communications port.
Three fully differential input channels feed into the
switching network. Each channel may be independent-
ly programmed with a gain between +1V/V and
+128V/V. These three differential channels may also be
configured to operate as five pseudo-differential input
channels. Two additional, fully differential system-cali-
bration channels allow system gain and offset error to
be measured. These system-calibration channels can
be used as additional differential signal channels when
dedicated gain and offset error correction channels are
not required.
Two chopper-stabilized buffers are available to isolate
the selected inputs from the capacitive loading of the
PGA and modulator. Three independent DACs provide
compensation for the DC component of the input signal
on each of the differential input channels.
The sigma-delta modulator converts the input signal into
a digital pulse train whose average duty cycle represents
the digitized signal information. The pulse train is then
processed by a digital decimation filter, resulting in a
conversion accuracy exceeding 16 bits. The digital filter’s
decimation factor is user-selectable, which allows the
conversion result’s resolution to be reduced to achieve a
higher output data rate. When used with 2.4576MHz or
1.024MHz master clocks, the decimation filter can be
programmed to produce zeros in its frequency response
at the line frequency and associated harmonics. This
ensures excellent line rejection without the need for fur-
ther postfiltering. In addition, the modulator sampling
frequency can be optimized for either lowest power dis-
sipation or highest output data rate.
MAX1403
+3V, 18-Bit, Low-Power, Multichannel,
Oversampling (Sigma-Delta) ADCThe MAX1403 can be configured to sequentially scan
all signal inputs and to transmit the results through the
serial interface with minimum communications over-
head. The output word contains a channel identification
tag to indicate the source of each conversion result.
Serial Digital InterfaceThe serial digital interface provides access to eight on-
chip registers (Figure 3). All serial-interface commands
begin with a write to the communications register
(COMM). On power-up, system reset, or interface reset,
the part expects a write to its communications register.
The COMM register access begins with a 0 start bit.
The COMM register R/Wbit selects a read or write
operation, and the register select bits (RS2, RS1, RS0)
select the register to be addressed. Hold DIN high
when not writing to COMM or another register (Table 1).
The serial interface consists of five signals: CS, SCLK,
DIN, DOUT, and INT. Clock pulses on SCLK shift bits
into DIN and out of DOUT. INTprovides an indication
that data is available. CSis a device chip-select input
as well as a clock polarity select input (Figure 4).
Using CSallows the SCLK, DIN, and DOUT signals to
be shared among several SPI-compatible devices.
When short on I/O pins, connect CSlow and operate
the serial digital interface in CPOL = 1, CPHA = 1 mode
using SCLK, DIN, and DOUT. This 3-wire interface mode
is ideal for opto-isolated applications. Furthermore, a
microcontroller (such as a PIC16C54 or 80C51) can
use a single bidirectional I/O pin for both sending to
DIN and receiving from DOUT (see Applications
Information), because the MAX1403 drives DOUT only
during a read cycle.
Additionally, connecting the INTsignal to a hardware
interrupt allows faster throughput and reliable, collision-
free data flow.
The MAX1403 features a mode where the raw modula-
tor data output is accessible. In this mode, the DOUT
and INTfunctions are reassigned (see the Modulator
Data Outputsection).
MAX1403
+3V, 18-Bit, Low-Power, Multichannel,
Oversampling (Sigma-Delta) ADC
Selecting Clock PolarityThe serial interface can be operated with the clock idling
either high or low. This is compatible with Motorola’s SPI
interface operated in CPOL = 1, CPHA = 1 mode or
CPOL = 0, CPHA = 1 mode. The clock polarity is deter-
mined by the state of SCLK at the falling edge of CS.
Ensure that the setup times t4/t12and t5/t13are not violat-
ed. If CSis connected to ground, resulting in no falling
edge on CS, SCLK must idle high (CPOL = 1, CPHA = 1).
Data-Ready Signal (DRDY bit true or IINNTT
= low)The data-ready signal indicates that new data may be
read from the 24-bit data register. After the end of a suc-
cessful data register read, the data-ready signal
becomes false. If a new measurement completes before
the data is read, the data-ready signal becomes false.
The data-ready signal becomes true again when new
data is available in the data register.
The MAX1403 provides two methods of monitoring the
data-ready signal. INTprovides a hardware solution
(active low when data is ready to be accessed), while
the DRDY bit in the COMM register provides a software
solution (active high).
Read data as soon as possible once data-ready
becomes true. This becomes increasingly important for
faster measurement rates. If the data read is delayed
significantly, a collision may result. A collision occurs
when a new measurement completes during a data-
register read operation. After a collision, information in
the data register is invalid. The failed read operation
must be completed even though the data is invalid.
Resetting the InterfaceReset the serial interface by clocking in 32 1s.
Resetting the interface does not affect the internal reg-
isters.
If continuous data output mode is in use, clock in eight
0s followed by 32 1s. More than 32 1s may be clocked
in, since a leading 0 is used as the start bit for all oper-
ations.
Continuous Data Output ModeWhen scanning the input channels (SCAN = 1), the ser-
ial interface allows the data register to be read repeat-
edly without requiring a write to the COMM register.
The initial COMM write (01111000) is followed by 24
clocks (DIN = high) to read the 24-bit data register.
Once the data register has been read, it can be read
again after the next conversion by writing another 24
clocks (DIN = high). Terminate the continuous data out-
put mode by writing to the COMM register with any
valid access.
Modulator Data Output (MDOUT = 1)Single-bit, raw modulator data is available at DOUT for
custom filtering when MDOUT = 1. INTprovides a mod-
ulator clock for data synchronization. Data is valid on
the falling edge of INT. Write operations can still be
performed; however, read operations are disabled.
After MDOUT is returned to 0, valid data is accessed
by the normal serial-interface read operation.
On-Chip Registers
Communications Register
0/DRDY: (Default = 0) Data Ready Bit. On a write, this
bit must be reset to 0 to signal the start of the Com-
munications Register data word. On a read, a 1 in this
location (0/DRDY) signifies that valid data is available in
the data register. This bit is reset after the data register
is read or, if data is not read, 0/DRDY will go low at the
end of the next measurement.
RS2, RS1, RS0:(Default = 0, 0, 0) Register Select
Bits. These bits select the register to be accessed
(Table 1).
R/W:(Default = 0) Read/Write Bit. When set high, the
selected register is read; when R/W= 0, the selected
register is written.
RESET:(Default = 0) Software Reset Bit. Setting this
bit high causes the part to be reset to its default power-
up condition (RESET = 0).
STDBY:(Default = 0) Standby Power-Down Bit. Setting
the STDBY bit places the part in “standby” condition,
shutting down everything except the serial interface
and the CLK oscillator.
FSYNC:(Default = 0) Filter Sync Bit. When FSYNC = 0,
conversions are automatically performed at a data rate
determined by CLK, FS1, FS0, MF1, and MF0 bits.
When FSYNC = 1, the digital filter and analog modulator
First Bit (MSB)(LSB)
Communications Register
MAX1403
+3V, 18-Bit, Low-Power, Multichannel,
Oversampling (Sigma-Delta) ADCare held in reset, inhibiting normal self-timed operation.
This bit may be used to convert on command to mini-
mize the settling time to valid output data, or to synchro-
nize operation of a number of MAX1403s. FSYNC does
not reset the serial interface or the 0/DRDY flag. To clear
the 0/DRDY flag while FSYNC is active, simply read the
data register.
Global Setup Register 1
A1, A0:(Default = 0, 0) Channel-Selection Control Bits.
These bits (combined with the state of the DIFF, M1,
and M0 bits) determine the channel selected for con-
version according to Tables 8, 9, and 10. These bits
are ignored if the SCAN bit is set.
MF1, MF0: (Default = 0, 0) Modulator Frequency Bits.
MF1 and MF0 determine the ratio of CLKIN oscillator fre-
quency to modulator operating frequency. They affect
the output data rate, the position of the digital filter notch
frequencies, and the power dissipation of the device.
Achieve lowest power dissipation with MF1 = 0 and MF0
= 0. Highest power dissipation and fastest output data
rate occur with these bits set to 1, 1 (Table 2).
CLK:(Default = 1) CLK Bit. The CLK bit is used in con-
junction with X2CLK to tell the MAX1403 the frequency
of the CLKIN input signal. If CLK = 0, a CLKIN input fre-
quency of 1.024MHz (2.048MHz for X2CLK = 1) is
expected. If CLK = 1, a CLKIN input frequency of
2.4576MHz (4.9152MHz for X2CLK = 1) is expected.
This bit affects the decimation factor in the digital filter
and thus the output data rate (Table 2).
FS1, FS0:(Default = 0, 1) Filter Selection Bits. These
bits (in conjunction with the CLK bit) control the deci-
mation ratio of the digital filter. They determine the out-
put data rate, the position of the digital filter frequency
response notches, and the noise present in the output
result (Table 2).
FAST:(Default 0) Fast Bit. FAST = 0 causes the digital
filter to perform a SINC3filter function on the modulator
data stream. The output data rate will be deter-
mined by the values in the CLK, FS1, FS0, MF1, and
MF0 bits (Table 2). The settling time for SINC3 function
is 3 ·[1 / (output data rate)]. In SINC3mode, the
MAX1403 automatically holds the DRDY signal false
(after any significant configuration change) until settled
data is available. FAST = 1 causes the digital filter to
perform a SINC1filter function on the modulator data
stream. The signal-to-noise ratio achieved with this filter
function is less than that of the SINC3filter; however,
SINC1settles in a single output sample period rather
than a minimum of three output sample periods for
SINC3. When switching from SINC1to SINC3mode, the
DRDY flag will be deasserted and reasserted after the
filter has fully settled. This mode change requires a
minimum of three samples.
Global Setup Register 2
SCAN:(Default = 0) Scan Bit. Setting this bit to a 1
causes sequential scanning of the input channels as
determined by DIFF, M1, and M0 (see Scanning(Scan-
Mode) section). When SCAN = 0, the MAX1403 repeat-
edly measures the unique channel selected by A1, A0,
DIFF, M1, and M0 (Table 4).
M1, M0:(Default 0, 0) Mode Control Bits. These bits
control access to the calibration channels CALOFF and
CALGAIN. When SCAN = 0, setting M1 = 0 and M0 = 1
selects the CALOFF input, and M1 = 1 and M0 = 0
selects the CALGAIN input (Table 3). When SCAN = 1
and M1 ≠M0, the scanning sequence includes both
CALOFF and CALGAIN inputs (Table 4). When SCAN is
set to 1 and the device is scanning the available input
channels, selection of either calibration mode (01 or 10)
will cause the scanning sequence to be extended to
include a conversion on both the CALGAIN+/CALGAIN-
input pair and the CALOFF+/CALOFF-input pair. The
Global Setup Register 2
Global Setup Register 1
MAX1403
+3V, 18-Bit, Low-Power, Multichannel,
Oversampling (Sigma-Delta) ADCexact sequence depends on the state of the DIFF bit
(Table 4). When scanning, the calibration channels use
the PGA gain, format, and DAC settings defined by the
contents of Transfer Function Register 3.
BUFF:(Default = 0) The BUFF bit controls operation of
the input buffer amplifiers. When this bit is 0, the inter-
nal buffers are bypassed and powered down. When
this bit is set high, the buffers drive the input sampling
capacitors and minimize the dynamic input load.
DIFF:(Default = 0) Differential/Pseudo-Differential Bit.
When DIFF = 0, the part is in pseudo-differential mode,
and AIN1–AIN5 are measured respective to AIN6, the
analog common. When DIFF = 1, the part is in differen-
tial mode with the analog inputs defined as AIN1/AIN2,
AIN3/AIN4, and AIN5/AIN6. The available input chan-
nels for each mode are tabulated in Table 5. Note that
DIFF also affects the scanning sequence when the part
is placed in SCAN mode (Table 4).
BOUT:(Default = 0) Burn-Out Current Bit. Setting BOUT
= 1 connects 100nA current sources to the selected ana-
log input channel. This mode is used to check that a
transducer has not burned out or opened circuit. The
burn-out current source must be turned off (BOUT = 0)
before measurement to ensure best linearity.
IOUT: (Default = 0) The IOUT bit controls the
Transducer Excitation Currents. A 0 in this bit disables
OUT1 and OUT2, effectively making these pins high-
impedance. A 1 in this location activates both IOUT1
and IOUT2, causing each pin to source 200µA.
X2CLK:(Default = 0) Times-Two Clock Bit. Setting this
bit to 1 selects a divide-by-2 prescaler in the clock sig-
nal path. This allows use of a higher frequency crystal
or clock source and improves immunity to asymmetric
clock sources.
Table 2. Data Output Rate vs. CLK, Filter Select, and Modulator Frequency Bits* Data rates offering noise-free 16-bit resolution.
Note: When FAST = 0, f-3dB = 0.262 ·Data Rate. When FAST = 1, f-3dB = 0.443 ·Data Rate.
Note: Default condition is in bold print.
Table 3. Special Modes Controlled by M1, M0 (SCAN = 0)
MAX1403
+3V, 18-Bit, Low-Power, Multichannel,
Oversampling (Sigma-Delta) ADC
Special Function Register (Write-Only)
MDOUT:(Default = 0) Modulator Out Bit. MDOUT = 0
enables data readout on the DOUT pin, the normal con-
dition for the serial interface. MDOUT = 1 changes the
function of the DOUT and INTpins, providing raw, sin-
gle-bit modulator output instead of the normal serial-
data interface output. This allows custom filtering
directly on the modulator output, without going through
the on-chip digital filter. The INTpin provides a clock to
indicate when the modulator data at DOUT should be
sampled (falling edge of INT). Note that in this mode,
the on-chip digital filter continues to operate normally.
When MDOUT is returned to 0, valid data may be
accessed through the normal serial-interface read
operation.
FULLPD:(Default = 0) Complete Power-Down Bit.
FULLPD = 1 forces the part into a complete power-down
condition, which includes the clock oscillator. The serial
interface continues to operate. The part requires a hard-
ware reset to recover correctly from this condition.
Note:Changing the reserved bits in the special-func-
tion register from the default status of all 0s will select
one of the reserved modes and the part will not operate
as expected. This register is a write-only register.
However, in the event that this register is mistakenly
read, clock 24 bits of data out of the part to restore it to
the normal interface-idle state.
Transfer-Function RegistersThe three transfer-function registers control the method
used to map the input voltage to the output codes. All
of the registers have the same format. The mapping of
control registers to associated channels depends on
the mode of operation and is affected by the state of
M1, M0, DIFF, and SCAN (Tables 8, 9, and 10).
Table 4. SCAN Mode Scanning
Sequences (SCAN = 1)
Table 5. Available Input Channels
(SCAN = 0)
Note:All other combinations reserved.
Special Function Register (Write-Only)
Transfer-Function Register
First Bit (MSB)(LSB)
First Bit (MSB)(LSB)
