Rainbow Electronics MX7705 User Manual
General Description
The MX7705 low-power, 2-channel, serial-output analog-to-digital converter (ADC) includes a sigma-delta
modulator with a digital filter to achieve 16-bit resolution
with no missing codes. This ADC is pin compatible and
software compatible with the AD7705. The MX7705 features an on-chip input buffer and programmable-gain
amplifier (PGA). The device offers an SPI-/QSPI-/
MICROWIRE-compatible serial interface.
The MX7705 operates from a single 2.7V to 5.25V supply.
The operating supply current is 320µA (typ) with a 3V
supply. Power-down mode reduces the supply current to
2µA (typ).
Self-calibration and system calibration allow the MX7705
to correct for gain and offset errors. Excellent DC performance (±0.003% FSR INL) and low noise (650nV) make
the MX7705 ideal for measuring low-frequency signals
with a wide dynamic range. The device accepts fully differential bipolar/unipolar inputs. An internal input buffer
allows for input signals with high source impedances. An
on-chip digital filter, with a programmable cutoff and output data rate, processes the output of the sigma-delta
modulator. The first notch frequency of the digital filter is
chosen to provide 150dB rejection of common-mode
50Hz or 60Hz noise and 98dB rejection of normal-mode
50Hz or 60Hz noise. A PGA and digital filtering allow signals to be directly acquired with little or no signal-conditioning requirements.
The MX7705 is available in 16-pin PDIP, SO, and
TSSOP packages.
Applications
Industrial Instruments
Weigh Scales
Strain-Gauge Measurements
Loop-Powered Systems
Flow and Gas Meters
Medical Instrumentation
Pressure Transducers
Thermocouple Measurements
RTD Measurements
Features
♦ Pin Compatible and Software Compatible with the
AD7705
♦ 16-Bit Sigma-Delta ADC
♦ Two Fully Differential Input Channels
♦ 0.003% Integral Nonlinearity with No Missing Codes
♦ Interface with Schmitt Triggers on Inputs
♦ Internal Analog Input Buffers
♦ PGA from 1 to 128
♦ Single (2.7V to 3.6V) or (4.75V to 5.25V) Supply
♦ Low Power
1mW (max), 3V Supply
2µA (typ) Power-Down Current
♦ SPI-/QSPI-/MICROWIRE-Compatible 3-Wire Serial
Interface
♦ 16-Pin PDIP, SO, and TSSOP Packages
MX7705
16-Bit, Low-Power, 2-Channel,
Sigma-Delta ADC
________________________________________________________________ Maxim Integrated Products 1
Pin Configuration
Ordering Information
19-3051; Rev 0; 10/03
For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at
1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com.
SPI/QSPI are trademarks of Motorola, Inc.
MICROWIRE is a trademark of National Semiconductor Corp.
*Future product—contact factory for availability.
PART TEMP RANGE PIN-PACKAGE
MX7705EPE* -40°C to +85°C 16 PDIP
MX7705EWE* -40°C to +85°C 16 WIDE SO
MX7705EUE -40°C to +85°C 16 TSSOP
TOP VIEW
SCLK
CLKIN
CLKOUT
RESET
AIN2+
AIN1+
AIN1-
1
2
3
MX7705
4
CS
5
6
7
8
16
GND
15
V
DD
DIN
14
DOUT
13
DRDY
12
AIN2-
11
REF-
10
REF+
9
PDIP/SO/TSSOP
MX7705
16-Bit, Low-Power, 2-Channel,
Sigma-Delta ADC
2 _______________________________________________________________________________________
ABSOLUTE MAXIMUM RATINGS
ELECTRICAL CHARACTERISTICS
(VDD= 3V or 5V, GND = 0, V
REF+
= 1.225V for VDD= 3V and V
REF+
= 2.5V for VDD= 5V, V
REF-
= GND, external f
CLKIN
=
2.4576MHz, CLKDIV bit = 0, C
REF+
to GND = 0.1µF, C
REF
- to GND = 0.1µF, TA= T
MIN
to T
MAX
, unless otherwise noted.)
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.
VDDto GND..............................................................-0.3V to +6V
All Other Pins to GND.................................-0.3V to (V
DD
+ 0.3V)
Maximum Current Input into Any Pin ..................................50mA
Continuous Power Dissipation (T
A
= +70°C)
PDIP (derate 10.5mW/°C above +70°C)......................842mW
TSSOP (derate 9.4mW/°C above +70°C) ....................755mW
Wide SO (derate 9.5mW/°C above +70°C)..................762mW
Operating Temperature Range ..........................-40°C to +85°C
Storage Temperature Range .............................-60°C to +150°C
Junction Temperature......................................................+150°C
Lead Temperature (soldering, 10s) .................................+300°C
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
DC ACCURACY
Resolution (No Missing Codes) 16 Bits
Output Noise Tables 1, 3 µV
Integral Nonlinearity INL Gain = 1, unbuffered ±0.003 %FSR
Unipolar Offset Error After calibration (Note 1) µV
Unipolar Offset Drift (Note 2) 0.5 µV/°C
Bipolar Zero Error After calibration (Note 1) µV
Bipolar Zero Drift (Note 2)
Positive Full-Scale Error After calibration (Notes 1, 3) µV
Full-Scale Drift (Notes 2, 4) 0.5 µV/°C
Gain Error After calibration (Notes 1, 5) µV
Gain Drift (Notes 2, 6) 0.5
Bipolar Negative Full-Scale Error After calibration ±0.003 %FSR
Bipolar Negative Full-Scale Drift
(Note 2)
ANALOG INPUTS (AIN1+, AIN1-, AIN2+, AIN2-)
AIN Differential Input Voltage
Range (Note 7)
AIN Absolute Input Voltage
Range (Note 8)
AIN DC Leakage Current Unselected input channel 1 nA
Gain = 1 to 4 0.5
Gain = 8 to 128 0.1
Gain = 1 to 4 1
Gain = 8 to 128 0.6
Unipolar input range 0
Bipolar input range
Unbuffered
Buffered
-V
GAIN
GND -
30mV
GND +
50mV
/
REF
V
REF
GAIN
V
REF
GAIN
V
DD
30mV
V
DD
1.5V
/
/
+
-
µV/°C
ppm of
FSR/°C
µV/°C
V
V
MX7705
16-Bit, Low-Power, 2-Channel,
Sigma-Delta ADC
_______________________________________________________________________________________ 3
ELECTRICAL CHARACTERISTICS (continued)
(VDD= 3V or 5V, GND = 0, V
REF+
= 1.225V for VDD= 3V and V
REF+
= 2.5V for VDD= 5V, V
REF-
= GND, external f
CLKIN
=
2.4576MHz, CLKDIV bit = 0, C
REF+
to GND = 0.1µF, C
REF
- to GND = 0.1µF, TA= T
MIN
to T
MAX
, unless otherwise noted.)
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
AIN Input Capacitance
AIN Input Sampling Rate f
Input Common-Mode Rejection CMR
Normal-Mode 50Hz Rejection
Normal-Mode 60Hz Rejection
Common-Mode 50Hz Rejection
Common-Mode 60Hz Rejection
EXTERNAL REFERENCE (REF+, REF-)
REF Differential Input Voltage
Range (Note 9)
RE F Ab sol ute Inp ut V ol tag e Rang e GND V
REF Input Capacitance Gain = 1 to 128 10 pF
REF Input Sampling Rate f
DIGITAL INPUTS (DIN, SCLK, CS, RESET)
Input High Voltage V
Input Low Voltage V
Input Hysteresis V
Input Current I
Input Capacitance 5pF
Gain = 1 34
Gain = 2 38
Gain = 4 45
Gain = 8 to 128 60
Gain = 1 to 128
s
VDD = 5V
V
DD
For filter notches of 25Hz, 50Hz,
±0.02 × f
For filter notches of 20Hz, 60Hz,
±0.02 × f
For filter notches of 25Hz, 50Hz,
±0.02 × f
For filter notches of 20Hz, 60Hz,
±0.02 × f
V
REF
HYST
IN
VDD = 4.75V to 5.25V 1.0 3.5
VDD = 2.7V to 3.6V 1.00 1.75
s
IH
VDD = 4.75V to 5.25V 0.8
IL
VDD = 2.7V to 3.6V 0.4
DIN, CS, RESET 250
SCLK 500
= 3V
NOTCH
NOTCH
NOTCH
NOTCH
Gain = 1 96
Gain = 2 105
Gain = 4 110
Gain = 8 to 128 130
Gain = 1 105
Gain = 2 110
Gain = 4 120
Gain = 8 to 128 130
f
CLKIN
64
98 dB
98 dB
150 dB
150 dB
f
CLKIN
64
2V
±1 µA
DD
pF
/
MHz
dB
V
V
/
MHz
V
mV
MX7705
16-Bit, Low-Power, 2-Channel,
Sigma-Delta ADC
4 _______________________________________________________________________________________
ELECTRICAL CHARACTERISTICS (continued)
(VDD= 3V or 5V, GND = 0, V
REF+
= 1.225V for VDD= 3V and V
REF+
= 2.5V for VDD= 5V, V
REF-
= GND, external f
CLKIN
=
2.4576MHz, CLKDIV bit = 0, C
REF+
to GND = 0.1µF, C
REF
- to GND = 0.1µF, TA= T
MIN
to T
MAX
, unless otherwise noted.)
CLKIN INPUT
CLKIN Input High Voltage V
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
CLKIN Input Low Voltage V
CLKIN Input Current I
DIGITAL OUTPUTS (DOUT, DRDY, CLKOUT)
Output Voltage Low V
Output Voltage High V
Tri-State Leakage Current I
Tri-State Output Capacitance C
SYSTEM CALIBRATION
Full-Scale Calibration Range
CLKINH
CLKINL
CLKIN
OH
OUT
VDD = 4.75V to 5.25V 3.5
VDD = 2.7V to 3.6V 2.5
VDD = 4.75V to 5.25V 0.8
VDD = 2.7V to 3.6V 0.4
VDD = 5V
OL
VDD = 3V
VDD = 5V
VDD = 3V
DOUT only ±10 µA
L
DOUT only 9 pF
GAIN = selected PGA gain (1 to 128)
(Note 10)
DOUT and DRDY,
I
= 800µA
SINK
CLKOUT,
I
= 10µA
SINK
DOUT and DRDY,
I
= 100µA
SINK
CLKOUT,
I
= 10µA
SINK
DOUT and DRDY,
I
CLKOUT,
I
DOUT and DRDY,
I
CLKOUT,
I
SOURCE
SOURCE
SOURCE
SOURCE
= 200µA
= 10µA
= 100µA
= 10µA
4.0
4.0
V
DD
0.6V
V
DD
0.6V
-1.05 ×
V
REF
GAIN
-
-
/
±10 µA
0.4
0.4
0.4
0.4
1.05 ×
V
/
REF
GAIN
V
V
V
V
V
-1.05 ×
V
REF
GAIN
0.8 ×
V
REF
GAIN
/
/
Offset Calibration Range
Input Span
GAIN = selected PGA gain (1 to 128)
(Note 10)
GAIN = selected PGA gain (1 to 128)
(Notes 10, 11)
1.05 ×
V
REF
GAIN
2.1 ×
V
REF
GAIN
/
V
/
V
MX7705
16-Bit, Low-Power, 2-Channel,
Sigma-Delta ADC
_______________________________________________________________________________________ 5
ELECTRICAL CHARACTERISTICS (continued)
(VDD= 3V or 5V, GND = 0, V
REF+
= 1.225V for VDD= 3V and V
REF+
= 2.5V for VDD= 5V, V
REF-
= GND, external f
CLKIN
=
2.4576MHz, CLKDIV bit = 0, C
REF+
to GND = 0.1µF, C
REF
- to GND = 0.1µF, TA= T
MIN
to T
MAX
, unless otherwise noted.)
POWER REQUIREMENTS
Power-Supply Voltage V
Power-Supply Current (Note 12) I
Power-Supply Rejection Ratio PSRR
EXTERNAL CLOCK TIMING SPECIFICATIONS
CLKIN Frequency f
Duty Cycle 40 60 %
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
DD
Unbuffered
f
CLKIN
gain =1 to 128
Buffered,
f
CLKIN
gain =1 to 128
Unbuffered,
f
CLKIN
DD
Buffered,
f
CLKIN
Power-down mode
(Note 13)
VDD = 4.75V to 5.25V (Note 14)
V
DD
CLKIN
(Note 15) 400 2500 kHz
=1MHz,
=1MHz,
= 2.4576MHz
= 2.4576MHz
= 2.7V to 3.6V (Note 14)
VDD = 5V 0.45
V
DD
VDD = 5V 0.7
V
DD
VDD = 5V,
gain = 1 to 4
VDD = 5V,
gain = 8 to 128
VDD = 3V,
gain = 1 to 4
V
DD
gain = 8 to 128
VDD = 5V,
gain = 1 to 4
VDD = 5V,
gain = 8 to 128
VDD = 3V,
gain = 1 to 4
V
DD
gain = 8 to 128
VDD = 5V 16
V
DD
= 3V 0.32
= 3V 0.6
= 3V,
= 3V,
= 3V 8
2.70 5.25 V
0.6
0.85
0.4
0.6
0.9
1.3
0.7
1.1
mA
µA
dB
MX7705
16-Bit, Low-Power, 2-Channel,
Sigma-Delta ADC
6 _______________________________________________________________________________________
TIMING CHARACTERISTICS
(VDD= 3V or 5V, GND = 0, V
REF+
= 1.225V for VDD= 3V and V
REF+
= 2.5V for VDD= 5V, V
REF-
= GND, external f
CLKIN
=
2.4576MHz, CLKDIV bit = 0, C
REF+
to GND = 0.1µF, C
REF
- to GND = 0.1µF, TA= T
MIN
to T
MAX
, unless otherwise noted.) (Note 16)
(Figures 8, 9)
DRDY High Time
Reset Pulse-Width Low 100 ns
DRDY Fall to CS Fall Setup Time t
CS Fall to SCLK Rise Setup Time t
SCLK Fall to DOUT Valid Delay t
SCLK Pulse-Width High t
SCLK Pulse-Width Low t
CS Rise to SCLK Rise Hold Time t
Bus Relinquish Time After SCLK
Rising Edge
SCLK Fall to DRDY Rise Delay t
DIN to SCLK Setup Time t
DIN to SCLK Hold Time t
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
1
2
VDD = 4.75V to 5.25V 0 80
3
VDD = 2.7V to 3.6V 0 100
4
5
6
t
10
VDD = 4.75V to 5.25V 60
7
VDD = 2.7V to 3.6V 100
8
9
500 /
f
CLKIN
120 ns
100 ns
100 ns
30 ns
20 ns
0ns
0ns
100 ns
s
ns
ns
MX7705
16-Bit, Low-Power, 2-Channel,
Sigma-Delta ADC
_______________________________________________________________________________________ 7
Note 1: These errors are in the order of the conversion noise shown in Tables 1 and 3. This applies after calibration at the given
temperature.
Note 2: Recalibration at any temperature removes these drift errors.
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.
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 (full-scale error - bipolar zero error) for bipolar ranges.
Note 6: Gain-error drift does not include unipolar offset drift or bipolar zero drift. Effectively, it is the drift of the part if only zero-
scale calibrations are performed.
Note 7: The analog input voltage range on AIN+ is given with respect to the voltage on AIN- on the MX7705.
Note 8: This common-mode voltage range is allowed, provided that the input voltage on analog inputs does not go more positive
than (V
DD
+ 30mV) or more negative than (GND - 30mV). Parts are functional with voltages down to (GND - 200mV), but
with increased leakage at high temperature.
Note 9: The REF differential voltage, V
REF
, is the voltage on REF+ referenced to REF- (V
REF
= V
REF+
- V
REF-)
.
Note 10: Guaranteed by design.
Note 11: These calibration and span limits apply, provided that the absolute voltage on the analog inputs does not exceed (V
DD
+
30mV) or go more negative than (GND - 30mV). The offset calibration limit applies to both the unipolar zero point and the
bipolar zero point.
Note 12: When using a crystal or ceramic resonator across the CLKIN and CLKOUT as the clock source for the device, the supply
current and power dissipation varies depending on the crystal or resonator type. Supply current is measured with the digital inputs connected to 0 or V
DD
, CLKIN connected to an external clock source, and CLKDIS = 1.
Note 13: If the external master clock continues to run in power-down mode, the power-down current typically increases to 67µA at
3V. When using a crystal or ceramic resonator across the CLKIN and CLKOUT as the clock source for the device, the
clock generator continues to run in power-down mode and the power dissipation depends on the crystal or resonator type
(see the Power-Down Modes section).
Note 14: Measured at DC and applied in the selected passband. PSRR at 50Hz exceeds 120dB with filter notches of 25Hz or 50Hz.
PSRR at 60Hz exceeds 120dB with filter notches of 20Hz or 60Hz. PSRR depends on both gain and V
DD
.
Note 15: Provide f
CLKIN
whenever the MX7705 is not in power-down mode. If no clock is present, the device can draw higher than
specified current and can possibly become uncalibrated.
Note 16: All input signals are specified with t
r
= tf= 5ns (10% to 90% of VDD) and timed from a voltage level of 1.6V.
TIMING CHARACTERISTICS (continued)
(VDD= 3V or 5V, GND = 0, V
REF+
= 1.225V for VDD= 3V and V
REF+
= 2.5V for VDD= 5V, V
REF-
= GND, external f
CLKIN
=
2.4576MHz, CLKDIV bit = 0, C
REF+
to GND = 0.1µF, C
REF
- to GND = 0.1µF, TA= T
MIN
to T
MAX
, unless otherwise noted.) (Note 16)
(Figures 8, 9)
GAIN
19086
27878
48485
8 to 128 91 93
PSRR (dB)
(V
= 5V)
DD
PSRR (dB)
(VDD = 3V)
MX7705
16-Bit, Low-Power, 2-Channel,
Sigma-Delta ADC
8 _______________________________________________________________________________________
Table 1. Output RMS Noise vs. Gain and Output Data Rate (VDD= 5V)
FILTER FIRST
NOTCH AND
OUTPUT DATA RATE
BUFFERED (f
UNBUFFERED (f
BUFFERED (f
UNBUFFERED (f
CLKIN
20Hz 5.24Hz 4.44 2.28 1.29 0.79 0.70 0.70 0.64 0.63
25Hz 6.55Hz 5.11 2.79 1.55 0.92 0.81 0.80 0.73 0.74
100Hz 26.2Hz 102.35 49.59 23.04 11.78 6.32 3.63 2.25 2.24
200Hz 52.4Hz 586.93 272.83 224.79 70.78 33.94 17.57 9.14 9.22
20Hz 5.24Hz 4.32 2.50 1.35 0.81 0.73 0.70 0.64 0.64
25Hz 6.55Hz 5.16 2.85 1.63 0.96 0.83 0.81 0.74 0.74
100Hz 26.2Hz 105.78 49.86 24.67 12.16 6.42 3.80 2.22 2.23
200Hz 52.4Hz 526.60 260.51
CLKIN
50Hz 13.1Hz 3.53 1.86 1.09 0.73 0.72 0.71 0.67 0.66
60Hz 15.72Hz 4.41 2.23 1.29 0.83 0.79 0.77 0.72 0.73
250Hz 65.5Hz 99.66 46.85 16.98 12.48 6.38 3.78 2.32 2.35
500Hz 131Hz 608.86 288.39 110.80 67.51 36.75 17.98 9.43 9.40
50Hz 13.1Hz 3.65 1.94 1.17 0.79 0.70 0.69 0.66 0.65
60Hz 15.72Hz 4.56 2.41 1.32 0.87 0.80 0.79 0.71 0.74
250Hz 65.5Hz 101.56 49.64 25.39 12.92 6.65 3.69 2.36 2.36
500Hz 131Hz 556.06 278.91 142.88 74.78 35.41 18.99 9.80 9.44
CLKIN
CLKIN
-3dB FREQUENCY
1 2 4 8 16 32 64 128
= 1MHz)
= 1MHz)
= 2.4576MHz)
= 2.4576MHz)
TYPICAL OUTPUT RMS NOISE (µV)
GAIN
132.16
67.25 34.09 18.20 8.95 9.08
MX7705
16-Bit, Low-Power, 2-Channel,
Sigma-Delta ADC
_______________________________________________________________________________________ 9
Table 2. Peak-to-Peak Resolution vs. Gain and Output Data Rate (VDD= 5V)
FILTER FIRST
NOTCH AND
OUTPUT DATA RATE
BUFFERED (f
UNBUFFERED (f
BUFFERED (f
UNBUFFERED (f
CLKIN
20Hz 5.24Hz 16 16 16 16 16 15 14 13
25Hz 6.55Hz 16 16 16 16 16 15 14 13
100Hz 26.2Hz 12 12 12 12 12 12 12 11
200Hz 52.4Hz 10 10 10 10 10 10 10 9
CLKIN
20Hz 5.24Hz 16 16 16 16 16 15 14 13
25Hz 6.55Hz 16 16 16 16 16 15 14 13
100Hz 26.2Hz 12 12 12 12 12 12 12 11
200Hz 52.4Hz 10 10 10 10 10 10 10 9
CLKIN
50Hz 13.1Hz 16 16 16 16 16 15 14 13
60Hz 15.72Hz 16 16 16 16 16 15 14 13
250Hz 65.5Hz 12 12 13 12 12 12 12 11
500Hz 131Hz 10 10 11 10 10 10 10 9
CLKIN
50Hz 13.1Hz 16 16 16 16 16 15 14 13
60Hz 15.72Hz 16 16 16 16 16 15 14 13
250Hz 65.5Hz 12 12 12 12 12 12 12 11
500Hz 131Hz 10 10 10 10 10 10 10 9
-3dB FREQUENCY
1 2 4 8 16 32 64 128
= 1MHz)
= 1MHz)
= 2.4576MHz)
= 2.4576MHz)
TYPICAL PEAK-TO-PEAK RESOLUTION (BITS)
GAIN
MX7705
16-Bit, Low-Power, 2-Channel,
Sigma-Delta ADC
10 ______________________________________________________________________________________
Table 3. Output RMS Noise vs. Gain and Output Data Rate (VDD= 3V)
FILTER FIRST
NOTCH AND
OUTPUT DATA RATE
BUFFERED (f
UNBUFFERED (f
BUFFERED (f
UNBUFFERED (f
CLKIN
20Hz 5.24Hz 3.52 1.84 2.19 0.73 0.66 0.62 0.62 0.62
25Hz 6.55Hz 4.24 2.23 1.19 0.84 0.74 0.69 0.69 0.69
100Hz 26.2Hz 50.36 25.12 12.06 6.04 3.38 2.23 1.70 1.69
200Hz 52.4Hz 268.02 175.98 65.77 34.89 16.73 8.76 4.70 4.70
20Hz 5.24Hz 3.58 1.92 1.13 0.72 0.66 0.64 0.61 0.62
25Hz 6.55Hz 4.16 2.27 1.27 0.83 0.74 0.70 0.69 0.67
100Hz 26.2Hz 50.48 23.89 12.10 5.90 3.26 0.70 1.66 1.63
200Hz 52.4Hz 256.43 135.78 65.62 33.18 16.65 8.47 4.66 4.68
CLKIN
50Hz 13.1Hz 2.84 1.68 2.00 0.71 0.67 0.65 0.63 0.61
60Hz 15.72Hz 3.27 1.84 1.12 0.78 0.75 0.70 0.68 0.67
250Hz 65.5Hz 47.90 24.43 12.56 6.48 3.45 2.32 1.64 1.66
500Hz 131Hz 281.03 104.19 69.58 34.59 17.44 9.20 5.16 4.92
50Hz 13.1Hz 3.04 1.74 1.03 0.72 0.64 0.64 0.62 0.63
60Hz 15.72Hz 3.35 1.80 1.13 0.81 0.73 0.69 0.67 0.68
250Hz 65.5Hz 49.63 23.82 13.03 6.23 3.42 2.22 1.68 1.65
500Hz 131Hz 279.13 134.82 69.47 35.42 17.47 9.55 4.90 5.18
CLKIN
CLKIN
-3dB FREQUENCY
1248163264128
= 1MHz)
= 1MHz)
= 2.4576MHz)
= 2.4576MHz)
TYPICAL OUTPUT RMS NOISE (µV)
GAIN
MX7705
16-Bit, Low-Power, 2-Channel,
Sigma-Delta ADC
______________________________________________________________________________________ 11
Table 4. Peak-to-Peak Resolution vs. Gain and Output Data Rate (VDD= 3V)
Typical Operating Characteristics
(VDD= 3V or 5V, V
REF+
= 1.225V for VDD= 3V, V
REF+
= 2.5V for VDD= 5V, V
REF
- = GND, TA= +25°C, unless otherwise noted.)
FILTER FIRST
NOTCH AND
OUTPUT DATA RATE
BUFFERED (f
CLKIN
-3dB FREQUENCY
1 2 4 8 16 32 64 128
= 1MHz)
TYPICAL PEAK-TO-PEAK RESOLUTION (BITS)
GAIN
20Hz 5.24Hz 16 16 16 16 15 14 13 12
25Hz 6.55Hz 16 16 16 16 15 14 13 12
100Hz 26.2Hz 12 12 12 12 12 12 12 11
200Hz 52.4Hz 10 10 10 10 10 10 10 9
UNBUFFERED (f
CLKIN
= 1MHz)
20Hz 5.24Hz 16 16 16 16 15 14 13 12
25Hz 6.55Hz 16 16 16 16 15 14 13 12
100Hz 26.2Hz 12 12 12 12 12 14 12 11
200Hz 52.4Hz 10 10 10 10 10 10 10 9
BUFFERED (f
= 2.4576MHz)
CLKIN
50Hz 13.1Hz 16 16 16 16 15 14 13 12
60Hz 15.72Hz 16 16 16 16 15 14 13 12
250Hz 65.5Hz 12 12 12 12 12 12 11 11
500Hz 131Hz 10 11 10 10 10 10 10 9
UNBUFFERED (f
= 2.4576MHz)
CLKIN
50Hz 13.1Hz 16 16 16 16 15 14 13 12
60Hz 15.72Hz 16 16 16 16 15 14 13 12
250Hz 65.5Hz 12 12 12 12 12 12 11 11
500Hz 131Hz 10 10 10 10 10 10 10 9
32776
32774
32772
32770
32768
32766
CODE READ
32764
32762
32760
32758
32756
TYPICAL OUTPUT NOISE
VDD = 5V,
= 2.5V
V
REF
0 2000
READING NUMBER
GAIN = 128
ODR = 60Hz
RMS NOISE = 1.3µV
16001200800400
MX7705 toc01
HISTOGRAM OF TYPICAL OUTPUT NOISE
400
VDD = 5V, V
GAIN = 128
ODR = 60Hz
300
200
OCCURENCE
100
0
32760
32761
REF
32762
= 2.5V
32763
32764
32765
CODE
RMS NOISE = 1.3µV
32768
32767
32766
32769
32770
32771
32772
MX7705 toc02
32773
OFFSET ERROR vs. SUPPLY VOLTAGE (3V)
0.0015
0.0010
0.0005
-0.0005
OFFSET ERROR (%FSR)
-0.0010
-0.0015
VDD = 3V
0
2.70 3.60
SUPPLY VOLTAGE (V)
MX7705 toc03
3.453.303.153.002.85
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