General Description
The MX7705 low-power, 2-channel, serial-output ana-
log-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 fea-
tures 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 320A (typ) with a 3V
supply. Power-down mode reduces the supply current to
2A (typ).
Self-calibration and system calibration allow the MX7705
to correct for gain and offset errors. Excellent DC perfor-
mance (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 dif-
ferential 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 out-
put 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 sig-
nals to be directly acquired with little or no signal-condi-
tioning 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
o Pin Compatible and Software Compatible with the
AD7705
o 16-Bit Sigma-Delta ADC
o Two Fully Differential Input Channels
o 0.003% Integral Nonlinearity with No Missing Codes
o Interface with Schmitt Triggers on Inputs
o Internal Analog Input Buffers
o PGA from 1 to 128
o Single (2.7V to 3.6V) or (4.75V to 5.25V) Supply
o Low Power
1mW (max), 3V Supply
2A (typ) Power-Down Current
o SPI-/QSPI-/MICROWIRE-Compatible 3-Wire Serial
Interface
o 16-Pin PDIP, SO, and TSSOP Packages
MX7705
16-Bit, Low-Power, 2-Channel,
Sigma-Delta ADC
________________________________________________________________ Maxim Integrated Products
1
16
15
14
13
12
11
10
9
1
2
3
4
5
6
7
8
SCLK
GND
V
DD
DIN
DOUT
DRDY
AIN2-
REF-
REF+
TOP VIEW
MX7705
PDIP/SO/TSSOP
CLKIN
CLKOUT
AIN2+
CS
RESET
AIN1+
AIN1-
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.
PART
TEMP RANGE
PIN-PACKAGE
MX7705EPE*
-40
C to +85C
16 PDIP
MX7705EWE*
-40
C to +85C
16 WIDE SO
MX7705EUE
-40
C to +85C
16 TSSOP
SPI/QSPI are trademarks of Motorola, Inc.
MICROWIRE is a trademark of National Semiconductor Corp.
*Future product--contact factory for availability.
MX7705
16-Bit, Low-Power, 2-Channel,
Sigma-Delta ADC
2
_______________________________________________________________________________________
ABSOLUTE MAXIMUM RATINGS
ELECTRICAL CHARACTERISTICS
(V
DD
= 3V or 5V, GND = 0, V
REF+
= 1.225V for V
DD
= 3V and V
REF+
= 2.5V for V
DD
= 5V, V
REF-
= GND, external f
CLKIN
=
2.4576MHz, CLKDIV bit = 0, C
REF+
to GND = 0.1F, C
REF
- to GND = 0.1F, T
A
= 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.
V
DD
to 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 +70C)......................842mW
TSSOP (derate 9.4mW/
C above +70C) ....................755mW
Wide SO (derate 9.5mW/
C above +70C)..................762mW
Operating Temperature Range ..........................-40
C to +85C
Storage Temperature Range .............................-60
C to +150C
Junction Temperature ......................................................+150C
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
V
Integral Nonlinearity
INL
Gain = 1, unbuffered
0.003
%FSR
Unipolar Offset Error
After calibration
(Note 1)
V
Unipolar Offset Drift
(Note 2)
0.5
V/C
Bipolar Zero Error
After calibration
(Note 1)
V
Gain = 1 to 4
0.5
Bipolar Zero Drift (Note 2)
Gain = 8 to 128
0.1
V/C
Positive Full-Scale Error
After calibration
(Notes 1, 3)
V
Full-Scale Drift
(Notes 2, 4)
0.5
V/C
Gain Error
After calibration
(Notes 1, 5)
V
Gain Drift
(Notes 2, 6)
0.5
ppm of
FSR/C
Bipolar Negative Full-Scale Error
After calibration
0.003
%FSR
Gain = 1 to 4
1
Bipolar Negative Full-Scale Drift
(Note 2)
Gain = 8 to 128
0.6
V/C
ANALOG INPUTS (AIN1+, AIN1-, AIN2+, AIN2-)
Unipolar input range
0
V
REF
/
GAIN
AIN Differential Input Voltage
Range (Note 7)
Bipolar input range
-V
REF
/
GAIN
V
REF
/
GAIN
V
Unbuffered
GND -
30mV
V
DD
+
30mV
AIN Absolute Input Voltage
Range (Note 8)
Buffered
GND +
50mV
V
DD
-
1.5V
V
AIN DC Leakage Current
Unselected input channel
1
nA
MX7705
16-Bit, Low-Power, 2-Channel,
Sigma-Delta ADC
_______________________________________________________________________________________
3
ELECTRICAL CHARACTERISTICS (continued)
(V
DD
= 3V or 5V, GND = 0, V
REF+
= 1.225V for V
DD
= 3V and V
REF+
= 2.5V for V
DD
= 5V, V
REF-
= GND, external f
CLKIN
=
2.4576MHz, CLKDIV bit = 0, C
REF+
to GND = 0.1F, C
REF
- to GND = 0.1F, T
A
= T
MIN
to T
MAX
, unless otherwise noted.)
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
Gain = 1
34
Gain = 2
38
Gain = 4
45
AIN Input Capacitance
Gain = 8 to 128
60
pF
AIN Input Sampling Rate
f
s
Gain = 1 to 128
f
CLKIN
/
64
MHz
Gain = 1
96
Gain = 2
105
Gain = 4
110
V
DD
= 5V
Gain = 8 to 128
130
Gain = 1
105
Gain = 2
110
Gain = 4
120
Input Common-Mode Rejection
CMR
V
DD
= 3V
Gain = 8 to 128
130
dB
Normal-Mode 50Hz Rejection
For filter notches of 25Hz, 50Hz,
0.02
f
NOTCH
98
dB
Normal-Mode 60Hz Rejection
For filter notches of 20Hz, 60Hz,
0.02
f
NOTCH
98
dB
Common-Mode 50Hz Rejection
For filter notches of 25Hz, 50Hz,
0.02
f
NOTCH
150
dB
Common-Mode 60Hz Rejection
For filter notches of 20Hz, 60Hz,
0.02
f
NOTCH
150
dB
EXTERNAL REFERENCE (REF+, REF-)
V
DD
= 4.75V to 5.25V
1.0
3.5
REF Differential Input Voltage
Range (Note 9)
V
REF
V
DD
= 2.7V to 3.6V
1.00
1.75
V
RE F Ab sol ute Inp ut V ol tag e Rang e
GND
V
DD
V
REF Input Capacitance
Gain = 1 to 128
10
pF
REF Input Sampling Rate
f
s
f
CLKIN
/
64
MHz
DIGITAL INPUTS (DIN, SCLK,
CS, RESET)
Input High Voltage
V
IH
2
V
V
DD
= 4.75V to 5.25V
0.8
Input Low Voltage
V
IL
V
DD
= 2.7V to 3.6V
0.4
V
DIN, CS, RESET
250
Input Hysteresis
V
HYST
SCLK
500
mV
Input Current
I
IN
1
A
Input Capacitance
5
pF
MX7705
16-Bit, Low-Power, 2-Channel,
Sigma-Delta ADC
4
_______________________________________________________________________________________
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
CLKIN INPUT
V
DD
= 4.75V to 5.25V
3.5
CLKIN Input High Voltage
V
CLKINH
V
DD
= 2.7V to 3.6V
2.5
V
V
DD
= 4.75V to 5.25V
0.8
CLKIN Input Low Voltage
V
CLKINL
V
DD
= 2.7V to 3.6V
0.4
V
CLKIN Input Current
I
CLKIN
10
A
DIGITAL OUTPUTS (DOUT,
DRDY, CLKOUT)
DOUT and DRDY,
I
SINK
= 800A
0.4
V
DD
= 5V
CLKOUT,
I
SINK
= 10A
0.4
DOUT and DRDY,
I
SINK
= 100A
0.4
Output Voltage Low
V
OL
V
DD
= 3V
CLKOUT,
I
SINK
= 10A
0.4
V
DOUT and DRDY,
I
SOURCE
= 200A
4.0
V
DD
= 5V
CLKOUT,
I
SOURCE
= 10A
4.0
DOUT and DRDY,
I
SOURCE
= 100A
V
DD
-
0.6V
Output Voltage High
V
OH
V
DD
= 3V
CLKOUT,
I
SOURCE
= 10A
V
DD
-
0.6V
V
Tri-State Leakage Current
I
L
DOUT only
10
A
Tri-State Output Capacitance
C
OUT
DOUT only
9
pF
SYSTEM CALIBRATION
Full-Scale Calibration Range
GAIN = selected PGA gain (1 to 128)
(Note 10)
-1.05
V
REF
/
GAIN
1.05
V
REF
/
GAIN
V
Offset Calibration Range
GAIN = selected PGA gain (1 to 128)
(Note 10)
-1.05
V
REF
/
GAIN
1.05
V
REF
/
GAIN
V
Input Span
GAIN = selected PGA gain (1 to 128)
(Notes 10, 11)
0.8
V
REF
/
GAIN
2.1
V
REF
/
GAIN
V
ELECTRICAL CHARACTERISTICS (continued)
(V
DD
= 3V or 5V, GND = 0, V
REF+
= 1.225V for V
DD
= 3V and V
REF+
= 2.5V for V
DD
= 5V, V
REF-
= GND, external f
CLKIN
=
2.4576MHz, CLKDIV bit = 0, C
REF+
to GND = 0.1F, C
REF
- to GND = 0.1F, T
A
= T
MIN
to T
MAX
, unless otherwise noted.)
MX7705
16-Bit, Low-Power, 2-Channel,
Sigma-Delta ADC
_______________________________________________________________________________________
5
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
POWER REQUIREMENTS
Power-Supply Voltage
V
DD
2.70
5.25
V
V
DD
= 5V
0.45
Unbuffered
f
CLKIN
=1MHz,
gain =1 to 128
V
DD
= 3V
0.32
V
DD
= 5V
0.7
Buffered,
f
CLKIN
=1MHz,
gain =1 to 128
V
DD
= 3V
0.6
V
DD
= 5V,
gain = 1 to 4
0.6
V
DD
= 5V,
gain = 8 to 128
0.85
V
DD
= 3V,
gain = 1 to 4
0.4
Unbuffered,
f
CLKIN
= 2.4576MHz
V
DD
= 3V,
gain = 8 to 128
0.6
V
DD
= 5V,
gain = 1 to 4
0.9
V
DD
= 5V,
gain = 8 to 128
1.3
V
DD
= 3V,
gain = 1 to 4
0.7
Buffered,
f
CLKIN
= 2.4576MHz
V
DD
= 3V,
gain = 8 to 128
1.1
mA
V
DD
= 5V
16
Power-Supply Current (Note 12)
I
DD
Power-down mode
(Note 13)
V
DD
= 3V
8
A
V
DD
= 4.75V to 5.25V
(Note 14)
Power-Supply Rejection Ratio
PSRR
V
DD
= 2.7V to 3.6V
(Note 14)
dB
EXTERNAL CLOCK TIMING SPECIFICATIONS
CLKIN Frequency
f
CLKIN
(Note 15)
400
2500
kHz
Duty Cycle
40
60
%
ELECTRICAL CHARACTERISTICS (continued)
(V
DD
= 3V or 5V, GND = 0, V
REF+
= 1.225V for V
DD
= 3V and V
REF+
= 2.5V for V
DD
= 5V, V
REF-
= GND, external f
CLKIN
=
2.4576MHz, CLKDIV bit = 0, C
REF+
to GND = 0.1F, C
REF
- to GND = 0.1F, T
A
= T
MIN
to T
MAX
, unless otherwise noted.)
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