18-Bit ADC with I2C Interface and Onboard Reference

42 Pages·2009·0.71 MB·English

by  Microchip Technology Inc

MCP3421
18-Bit Analog-to-Digital Converter
2
with I C Interface and On-Board Reference
Features Description

• 18-bit ΔΣ ADC in a SOT-23-6 package The MCP3421 is a single channel low-noise, high
• Differential Input Operation accuracy ΔΣ A/D converter with differential inputs and
up to 18 bits of resolution in a small SOT-23-6 package.
• Self Calibration of Internal Offset and Gain Per
The on-board precision 2.048V reference voltage
Each Conversion
enables an input range of ±2.048V differentially
• On-Board Voltage Reference: (Δvoltage = 4.096V). The device uses a two-wire I2C
- Accuracy: 2.048V±0.05% compatible serial interface and operates from a single
- Drift: 15ppm/°C 2.7V to 5.5V power supply.
• On-Board Programmable Gain Amplifier (PGA): The MCP3421 device performs conversion at rates of
- Gains of 1,2, 4 or 8 3.75, 15, 60, or 240 samples per second (SPS)
• On-Board Oscillator depending on the user controllable configuration bit
settings using the two-wire I2C serial interface. This
• INL: 10ppm of FSR (FSR = 4.096V/PGA)
device has an on-board programmable gain amplifier
• Programmable Data Rate Options:
(PGA). The user can select the PGA gain of x1, x2, x4,
- 3.75SPS (18bits)
or x8 before the analog-to-digital conversion takes
- 15SPS (16bits) place. This allows the MCP3421 device to convert a
- 60SPS (14bits) smaller input signal with high resolution. The device
- 240SPS (12bits) has two conversion modes: (a) Continuous mode and
(b) One-Shot mode. In One-Shot mode, the device
• One-Shot or Continuous Conversion Options
enters a low current standby mode automatically after
• Low Current Consumption:
one conversion. This reduces current consumption
- 145µA typical greatly during idle periods.
(V =3V, Continuous Conversion)
DD
The MCP3421 device can be used for various high
- 39µA typical
accuracy analog-to-digital data conversion applications
(V =3V, One-Shot Conversion with 1SPS)
DD where design simplicity, low power, and small footprint
• Supports I2C Serial Interface:
are major considerations.
- Standard, Fast and High Speed Modes
• Single Supply Operation: 2.7Vto5.5V Block Diagram
• Extended Temperature Range: -40°Cto+125°C
V V
SS DD
Typical Applications
Voltage Reference
• Portable Instrumentation
(2.048V)
• Weigh Scales and Fuel Gauges
• Temperature Sensing with RTD, Thermistor, and Gain = 1, 2, 4, or 8 VREF
Thermocouple
V +
IN
• Bridge Sensing for Pressure, Strain, and Force.
ΔΣ ADC Clock
PGA
Converter Oscillator
Package Types
SOT-23-6 MCP3421 VIN-
VIN+ 1 6 VIN- I2C Interface
VSS 2 5 VDD
SCL 3 4 SDA
SCL SDA
© 2009 Microchip Technology Inc. DS22003E-page 1
MCP3421
NOTES:
DS22003E-page 2 © 2009 Microchip Technology Inc.
MCP3421
1.0 ELECTRICAL †Notice: Stresses above those listed under “Maximum Rat-
CHARACTERISTICS ings” may cause permanent damage to the device. This is a
stress rating only and functional operation of the device at
those or any other conditions above those indicated in the
1.1 Absolute Maximum Ratings†
operational listings of this specification is not implied.
Exposure to maximum rating conditions for extended periods
V ...................................................................................7.0V
DD
may affect device reliability.
All inputs and outputs w.r.t V ............... –0.3V to V +0.3V
SS DD
Differential Input Voltage ......................................|V - V |
DD SS
Output Short Circuit Current ................................Continuous
Current at Input Pins ....................................................±2mA
Current at Output and Supply Pins ............................±10mA
Storage Temperature....................................-65°C to +150°C
Ambient Temp. with power applied...............-55°C to +125°C
ESD protection on all pins ................≥ 6kVHBM, ≥ 400VMM
Maximum Junction Temperature (T )..........................+150°C
J
1.2 Electrical Specifications
ELECTRICAL CHARACTERISTICS
Electrical Specifications: Unless otherwise specified, all parameters apply for T = -40°C to +85°C, V = +5.0V, V = 0V,
A DD SS
V + = V - = V /2. All ppm units use 2*V as full scale range.
IN IN REF REF
Parameters Sym Min Typ Max Units Conditions
Analog Inputs
Differential Input Range — ±2.048/PGA — V V = V + - V -
IN IN IN
Common-Mode Voltage Range V -0.3 — V +0.3 V
SS DD
(absolute) (Note1)
Differential Input Impedance Z (f) — 2.25/PGA — MΩ During normal mode operation
IND
(Note2)
Common Mode input Z (f) — 25 — MΩ PGA = 1, 2, 4, 8
INC
Impedance
System Performance
Resolution and No Missing 12 — — Bits DR = 240SPS
Codes (Note8)
14 — — Bits DR = 60SPS
16 — — Bits DR = 15SPS
18 — — Bits DR = 3.75SPS
Data Rate (Note3) DR 176 240 328 SPS S1,S0 = ‘00’, (12 bits mode)
44 60 82 SPS S1,S0 = ‘01’, (14 bits mode)
11 15 20.5 SPS S1,S0 = ‘10’, (16 bits mode)
2.75 3.75 5.1 SPS S1,S0 = ‘11’, (18 bits mode)
Output Noise — 1.5 — µV T = +25°C, DR = 3.75 SPS,
RMS A
PGA = 1, V = 0
IN
Integral Nonlinearity (Note4) INL — 10 35 ppm of DR = 3.75 SPS
FSR (Note6)
Internal Reference Voltage V — 2.048 — V
REF
Note 1: Any input voltage below or greater than this voltage causes leakage current through the ESD diodes at the input pins.
This parameter is ensured by characterization and not 100% tested.
2: This input impedance is due to 3.2pF internal input sampling capacitor.
3: The total conversion speed includes auto-calibration of offset and gain.
4: INL is the difference between the endpoints line and the measured code at the center of the quantization band.
5: Includes all errors from on-board PGA and V .
REF
6: Full Scale Range (FSR) = 2 x 2.048/PGA = 4.096/PGA.
7: This parameter is ensured by characterization and not 100% tested.
8: This parameter is ensured by design and not 100% tested.
© 2009 Microchip Technology Inc. DS22003E-page 3
MCP3421
ELECTRICAL CHARACTERISTICS (CONTINUED)
Electrical Specifications: Unless otherwise specified, all parameters apply for T = -40°C to +85°C, V = +5.0V, V = 0V,
A DD SS
V + = V - = V /2. All ppm units use 2*V as full scale range.
IN IN REF REF
Parameters Sym Min Typ Max Units Conditions
Gain Error (Note5) — 0.05 0.35 % PGA = 1, DR = 3.75 SPS
PGA Gain Error Match (Note5) — 0.1 — % Between any 2 PGA gains
Gain Error Drift (Note5) — 15 — ppm/°C PGA=1, DR=3.75 SPS
Offset Error V — 15 40 µV Tested at PGA = 1
OS
V = 5.0V and DR = 3.75 SPS
DD
Offset Drift vs. Temperature — 50 — nV/°C V = 5.0V
DD
Common-Mode Rejection — 105 — dB at DC and PGA =1,
— 110 — dB at DC and PGA =8,
T = +25°C
A
Gain vs. V — 5 — ppm/V T = +25°C, V = 2.7V to 5.5V,
DD A DD
PGA = 1
Power Supply Rejection at DC — 100 — dB T = +25°C, V = 2.7V to 5.5V,
A DD
PGA = 1
Power Requirements
Voltage Range V 2.7 — 5.5 V
DD
Supply Current during I — 155 190 µA V = 5.0V
DDA DD
Conversion
— 145 — µA V = 3.0V
DD
Supply Current during Standby I — 0.1 0.5 µA
DDS
Mode
I2C Digital Inputs and Digital Outputs
High level input voltage V 0.7 V — V V
IH DD DD
Low level input voltage V — — 0.3V V
IL DD
Low level output voltage V — — 0.4 V I = 3mA, V = +5.0V
OL OL DD
Hysteresis of Schmitt Trigger V 0.05V — — V f = 100kHz
HYST DD SCL
for inputs (Note7)
Supply Current when I2C bus I — — 10 µA
DDB
line is active
Input Leakage Current I — — 1 µA V = 5.5V
ILH IH
I -1 — — µA V = GND
ILL IL
Pin Capacitance and I2C Bus Capacitance
Pin capacitance C — — 10 pF
PIN
I2C Bus Capacitance C — — 400 pF
b
Note 1: Any input voltage below or greater than this voltage causes leakage current through the ESD diodes at the input pins.
This parameter is ensured by characterization and not 100% tested.
2: This input impedance is due to 3.2pF internal input sampling capacitor.
3: The total conversion speed includes auto-calibration of offset and gain.
4: INL is the difference between the endpoints line and the measured code at the center of the quantization band.
5: Includes all errors from on-board PGA and V .
REF
6: Full Scale Range (FSR) = 2 x 2.048/PGA = 4.096/PGA.
7: This parameter is ensured by characterization and not 100% tested.
8: This parameter is ensured by design and not 100% tested.
DS22003E-page 4 © 2009 Microchip Technology Inc.
MCP3421
TEMPERATURE SPECIFICATIONS
Electrical Characteristics: Unless otherwise indicated, T = -40°C to +85°C, V = +5.0V, V = 0V.
A DD SS
Parameters Sym Min Typ Max Units Conditions
Temperature Ranges
Specified Temperature Range T -40 — +85 °C
A
Operating Temperature Range T -40 — +125 °C
A
Storage Temperature Range T -65 — +150 °C
A
Thermal Package Resistances
Thermal Resistance, 6L SOT-23 θ — 190.5 — °C/W
JA
© 2009 Microchip Technology Inc. DS22003E-page 5
MCP3421
NOTES:
DS22003E-page 6 © 2009 Microchip Technology Inc.
MCP3421
2.0 TYPICAL PERFORMANCE CURVES
Note: The graphs and tables provided following this note are a statistical summary based on a limited number of
samples and are provided for informational purposes only. The performance characteristics listed herein
are not tested or guaranteed. In some graphs or tables, the data presented may be outside the specified
operating range (e.g., outside specified power supply range) and therefore outside the warranted range.
Note: Unless otherwise indicated, T = -40°C to +85°C, V = +5.0V, V = 0V, V + = V - = V /2.
A DD SS IN IN REF
% of FSR)..000045 ms) 107..05 VTAD D= = + 255V°C PGAP =G A2 = 1
onlinearity (..000023 PGA P=G 1A =P 4GA =P G2A = 8 Noise (µV, r 25..50 PGPGA A= =8 4
N.001
al
gr
e.000 0.0
Int 2.5 3 3.5 4 4.5 5 5.5 -100 -75 -50 -25 0 25 50 75 100
V (V) Input Voltage (% of Full Scale)
DD
FIGURE 2-1: INL vs. Supply Voltage FIGURE 2-4: Output Noise vs. Input
(V ). Voltage.
DD
3.0
PGA = 1
0.003
Integral Nonlinearity (% of FSR) 00..000012 PGA = 1VDD = 5 V VDD = 2.7V Total Error (mV) --21012.....00000 PPPGGGAAA === 284
0 -3.0
-60 -40 -20 0 20 40 60 80 100120140 -100 -75 -50 -25 0 25 50 75 100
Temperature (oC) Input Voltage (% of Full Scale)
FIGURE 2-2: INL vs. Temperature. FIGURE 2-5: Total Error vs. Input Voltage.
20 0.4
15 VDD = 5V 0.3 VDD = 5.0V
or (µV) 105 PGA = 2 PGA = 4 PGA = 8 % of FSR) 00..12 PGA = 2PGA = 1
Offset Err --11-5050 PGA = 1 Gain Error ( ---000...3210 PGA = 4
PGA = 8
-20 -0.4
-60 -40 -20 0 20 40 60 80 100 120 140 -60 -40 -20 0 20 40 60 80 100 120 140
Temperature (°C) Temperature (°C)
FIGURE 2-3: Offset Error vs. FIGURE 2-6: Gain Error vs. Temperature.
Temperature.
© 2009 Microchip Technology Inc. DS22003E-page 7
MCP3421
Note: Unless otherwise indicated, T = -40°C to +85°C, V = +5.0V, V = 0V, V + = V - = V /2.
A DD SS IN IN REF
220
5
200
4
VDD = 5V %)
I(µA)DDA 111468000 ator Drift ( 23 VDD = 2.7V
VDD = 2.7V cill 1
120 Os 0 VDD = 5.0V
100
-1
-60 -40 -20 0 20 40 60 80 100 120 140
-60 -40 -20 0 20 40 60 80 100 120 140
Temperature (oC) Temperature (°C)
FIGURE 2-7: I vs. Temperature. FIGURE 2-10: OSC Drift vs. Temperature.
DDA
0
600
-10 Data Rate = 3.75 SPS
500 -20
I (nA)DDS 234000000 nitude (dB) -----7654300000
100 VDD = 5V Mag --9800
VDD = 2.7V -100
0 -110
-60 -40 -20 0 20 40 60 80 100 120 140 -120
00..11 11 1010 101000 11k000 1010k000
Temperature (oC) Input Signal Frequency (Hz)
FIGURE 2-8: I vs. Temperature. FIGURE 2-11: Frequency Response.
DDS
9
8 VDD = 5V
7
VDD = 4.5V
A) 6
μ 5
(B 4 VDD = 3.3V
D
D
I 3
2 VDD = 2.7V
1
0
-60 -40 -20 0 20 40 60 80 100 120 140
Temperature (oC)
FIGURE 2-9: I vs. Temperature.
DDB
DS22003E-page 8 © 2009 Microchip Technology Inc.
MCP3421
3.0 PIN DESCRIPTIONS
The descriptions of the pins are listed in Table3-1.
TABLE 3-1: PIN FUNCTION TABLE
MCP3421 Symbol Description
1 V + Positive Differential Analog Input Pin
IN
2 V Ground Pin
SS
3 SCL Serial Clock Input Pin of the I2C Interface
4 SDA Bidirectional Serial Data Pin of the I2C Interface
5 V Positive Supply Voltage Pin
DD
6 V - Negative Differential Analog Input Pin
IN
3.1 Analog Inputs (VIN+, VIN-) 3.2 Supply Voltage (VDD, VSS)
V + and V - are differential signal input pins. The V is the power supply pin for the device. This pin
IN IN DD
MCP3421 device accepts a fully differential analog requires an appropriate bypass capacitor of about
input signal which is connected on the V + and V - 0.1µF (ceramic) to ground. An additional 10µF
IN IN
input pins. The differential voltage that is converted is capacitor (tantalum) in parallel is also recommended
defined by V = (V + - V -) where V + is the voltage to further attenuate high frequency noise present in
IN IN IN IN
applied at the V + pin and V - is the voltage applied some application boards. The supply voltage (V )
IN IN DD
at the V - pin. The user can also connect V - pin to must be maintained in the 2.7V to 5.5V range for
IN IN
V for a single-ended operation. See Figure6-4 for specified operation.
SS
differential and single-ended connection examples.
V is the ground pin and the current return path of the
SS
The input signal level is amplified by the programmable device. The user must connect the V pin to a ground
SS
gain amplifier (PGA) before the conversion. The plane through a low impedance connection. If an
differential input voltage should not exceed an absolute analog ground path is available in the application PCB
of (V /PGA) for accurate measurement, where V (printed circuit board), it is highly recommended that
REF REF
is the internal reference voltage (2.048V) and PGA is the V pin be tied to the analog ground path or
SS
the PGA gain setting. The converter output code will isolated within an analog ground plane of the circuit
saturate if the input range exceeds (V /PGA). board.
REF
The absolute voltage range on each of the differential
input pins is from V -0.3V to V +0.3V. Any voltage 3.3 Serial Clock Pin (SCL)
SS DD
above or below this range will cause leakage currents SCL is the serial clock pin of the I2C interface. The
through the Electrostatic Discharge (ESD) diodes at
MCP3421 acts only as a slave and the SCL pin
the input pins. This ESD current can cause unexpected
accepts only external serial clocks. The input data
performance of the device. The common mode of the
from the Master device is shifted into the SDA pin on
analog inputs should be chosen such that both the
the rising edges of the SCL clock and output from the
differential analog input range and the absolute voltage
MCP3421 occurs at the falling edges of the SCL clock.
range on each pin are within the specified operating
The SCL pin is an open-drain N-channel driver.
range defined in Section1.0 “Electrical
Therefore, it needs a pull-up resistor from the V line
Characteristics” and Section4.0 “Description of to the SCL pin. Refer to Section5.3 “I2C DSDerial
Device Operation”. Communications” for more details of I2C Serial
See Section4.5 “Input Voltage Range” for more Interface communication.
details of the input voltage range.
Figure3-1 shows the input structure of the device. The
device uses a switched capacitor input stage at the
front end. C is the package pin capacitance and
PIN
typically about 4pF. D and D are the ESD diodes.
1 2
C is the differential input sampling capacitor.
SAMPLE
© 2009 Microchip Technology Inc. DS22003E-page 9
MCP3421
3.4 Serial Data Pin (SDA) Typical range of the pull-up resistor value for SCL and
SDA is from 5kΩ to 10kΩ for standard (100kHz) and
SDA is the serial data pin of the I2C interface. The SDA
fast (400kHz) modes, and less than 1kΩ for high
pin is used for input and output data. In read mode, the
speed mode (3.4MHz). The High-Speed mode is not
conversion result is read from the SDA pin (output). In recommended for V less than 2.7V.
DD
write mode, the device configuration bits are written
(input) though the SDA pin. The SDA pin is an open-
drain N-channel driver. Therefore, it needs a pull-up
resistor from the V line to the SDA pin. Except for
DD
start and stop conditions, the data on the SDA pin must
be stable during the high period of the clock. The high
or low state of the SDA pin can only change when the
clock signal on the SCL pin is low. Refer to Section5.3
“I2C Serial Communications” for more details of I2C
Serial Interface communication.

V
DD
Sampling
Switch
RSS VIN+,VIN- D1 VT = 0.6V SS RS
V 4CPpIFN D2 VT = 0.6V (IL~E±A1KAnGAE) C(3S.2AMpPFL)E
V
SS
Legend:
V = Signal Source I = Leakage Current at Analog Pin
LEAKAGE
R = Source Impedance SS = Sampling Switch
SS
V +, V - = Analog Input Pin R = Sampling Switch Resistor
IN IN S
C = Input Pin Capacitance C = Sample Capacitance
PIN SAMPLE
V = Threshold Voltage D , D = ESD Protection Diode
T 1 2
FIGURE 3-1: Equivalent Analog Input Circuit.
DS22003E-page 10 © 2009 Microchip Technology Inc.