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Isolated Sigma-Delta Modulator

Data Sheet

AD7400A

Rev. D Document Feedback

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FEATURES

10 MHz clock rate

Second-order modulator

16 bits, no missing codes

±2 LSB INL typical at 16 bits

1.5 µV/°C typical offset drift

On-board digital isolator

On-board reference

±250 mV analog input range

Low power operation: 15.5 mA typical at 5.5 V

−40°C to +125°C operating range

16-lead SOIC package

AD7401A, external clock version in 16-lead SOIC

Safety and regulatory approvals

UL recognition

5000 V rms for 1 minute per UL 1577

CSA Component Acceptance Notice #5A

VDE Certificate of Conformity

DIN V VDE V 0884-10 (VDE V 0884-10):2006-12

IORM

= 891 V peak

APPLICATIONS

AC motor controls

Shunt current monitoring

Data acquisition systems

Analog-to-digital and opto-isolator replacements

GENERAL DESCRIPTION

The AD7400A

is a second-order, Σ-Δ modulator that converts

an analog input signal into a high speed, 1-bit data stream with

on-chip digital isolation based on Analog Devices, Inc., iCoupler®

technology. The AD7400A operates from a 5 V power supply

and accepts a differential input signal of ±250 mV (±320 mV

full scale). The analog input is sampled continuously by the

analog modulator, eliminating the need for external sample-

and-hold circuitry. The input information is contained in the

output stream as a density of ones with a data rate of 10 MHz.

The original information can be reconstructed with an appropriate

digital filter. The serial I/O can use a 5 V or a 3 V supply (V

DD2

The serial interface is digitally isolated. High speed CMOS,

combined with monolithic air core transformer technology,

means the on-chip isolation provides outstanding performance

characteristics superior to alternatives such as optocoupler

devices. The part contains an on-chip reference and has an

operating temperature range of −40°C to +125°C. The AD7400A

is offered in a 16-lead SOIC package.

Protected by U.S. Patents 5,952,849; 6,873,065; and 7,075,329.

FUNCTIONAL BLOCK DIAGRAM

DD1

DD2

–

Σ-Δ ADC

CONTROL LOGIC

AD7400A

BUF

T/H

REF

UPDATE

GND

MDAT

MCLKOUT

ENCODE

DECODE

WATCHDOG

UPDATE

07077-001

Figure 1.

Summary of content (20 pages)

PAGE 1
Isolated Sigma-Delta Modulator AD7400A Data Sheet FEATURES GENERAL DESCRIPTION 10 MHz clock rate Second-order modulator 16 bits, no missing codes ±2 LSB INL typical at 16 bits 1.5 µV/°C typical offset drift On-board digital isolator On-board reference ±250 mV analog input range Low power operation: 15.5 mA typical at 5.
PAGE 2
AD7400A Data Sheet TABLE OF CONTENTS Features .............................................................................................. 1 Terminology .................................................................................... 12 Applications ....................................................................................... 1 Theory of Operation ...................................................................... 13 General Description ..............................................
PAGE 3
Data Sheet AD7400A SPECIFICATIONS VDD1 = 4.5 V to 5.5 V, VDD2 = 3 V to 5.5 V, VIN+ = −200 mV to +200 mV, except where specified, and VIN− = 0 V (single-ended); TA = −40°C to +125°C, except where specified; fMCLK = 10 MHz, tested with Sinc3 filter, 256 decimation rate, as defined by Verilog code, unless otherwise noted. Table 1. Parameter STATIC PERFORMANCE Resolution Integral Nonlinearity 2 Min Y Version 1 Typ Max 16 ±2 ±4 ±4 Differential Nonlinearity2 Offset Error2 Offset Drift vs.
PAGE 4
AD7400A Data Sheet TIMING SPECIFICATIONS VDD1 = 4.5 V to 5.5 V, VDD2 = 3 V to 5.5 V, TA = −40°C to +125°C, except where specified. 1 Table 2. Parameter fMCLKOUT 2 t1 3 t2 3 t3 t4 Limit at tMIN, tMAX 10 9/11 40 10 0.4 × tMCLKOUT 0.
PAGE 5
Data Sheet AD7400A INSULATION AND SAFETY-RELATED SPECIFICATIONS Table 3. Parameter Input-to-Output Momentary Withstand Voltage Minimum External Air Gap (Clearance) Symbol VISO L(I01) Value 5000 min 8.1 min Unit V rms mm Minimum External Tracking (Creepage) L(I02) 7.46 min mm Minimum Internal Gap (Internal Clearance) Tracking Resistance (Comparative Tracking Index) Isolation Group CTI 0.
PAGE 6
AD7400A Data Sheet DIN V VDE V 0884-10 (VDE V 0884-10) INSULATION CHARACTERISTICS This isolator is suitable for reinforced electrical isolation only within the safety limit data. Maintenance of the safety data is ensured by means of protective circuits. Table 5.
PAGE 7
Data Sheet AD7400A ABSOLUTE MAXIMUM RATINGS TA = 25°C, unless otherwise noted. All voltages are relative to their respective ground. Table 6.
PAGE 8
AD7400A Data Sheet PIN CONFIGURATION AND FUNCTION DESCRIPTIONS VDD1 1 16 GND2 VIN+ 2 15 NC NC 4 AD7400A 14 VDD2 TOP VIEW (Not to Scale) 13 MCLKOUT NC 5 12 NC NC 6 11 MDAT VDD1/NC 7 10 NC GND1 8 9 GND2 NC = NO CONNECT 07077-104 VIN– 3 Figure 5. Pin Configuration Table 8. Pin Function Descriptions Pin No. Mnemonic Description 1 VDD1 2 3 4 to 6, 10, 12, 15 7 VIN+ VIN− NC VDD1/NC 8 9, 16 11 GND1 GND2 MDAT 13 MCLKOUT 14 VDD2 Supply Voltage, 4.5 V to 5.5 V.
PAGE 9
Data Sheet AD7400A TYPICAL PERFORMANCE CHARACTERISTICS TA = 25°C, using 20 kHz brickwall filter, unless otherwise noted. 110 –85 100 90 –80 80 SINAD (dB) PSRR (dB) 70 60 50 40 –75 –70 30 –65 VDD1 = VDD2 = 5V NO DECOUPLING CAPACITOR VRIPPLE = 200mV SINE WAVE ON VDD1 0 100 1k 10k VDD1 = VDD2 = 5V TA = 25°C 100k 1M 10M SUPPLY RIPPLE FREQUENCY (Hz) –60 50 07077-005 10 100 150 200 250 300 350 50,000 60,000 INPUT AMPLITUDE (mV) 07077-008 20 Figure 9. SINAD vs. VIN Figure 6.
PAGE 10
AD7400A Data Sheet 3.9 500 +125°C 450 +85°C 3.7 400 3.5 300 IDD2 (mA) OFFSET (µV) 350 250 200 150 +25°C 3.3 –40°C 3.1 2.9 100 2.7 VDD1 = VDD2 = 5V TA = 25°C –40 –20 VDD2 = VDD1 = 5V 0 20 40 60 80 100 120 TEMPERATURE (°C) 2.5 –0.4 –0.3 –0.2 –0.1 0 0.1 0.2 0.3 0.4 VIN DC INPUT VOLTAGE (V) 07077-014 0 –60 07077-012 50 Figure 15. IDD2 vs. VIN at Various Temperatures Figure 12. Offset Drift vs. Temperature 0.20 –30 0.15 –40 0.10 –50 VDD1 = VDD2 = 4.
PAGE 11
Data Sheet AD7400A 11.0 10.8 10.6 VDD1 = VDD2 = 4.5V 10.2 10.0 9.8 VDD1 = VDD2 = 5.25V 9.6 9.4 VDD1 = VDD2 = 5V TEMPERATURE (°C) 07077-024 95 105 85 75 65 55 45 35 25 5 15 –5 –15 –25 9.0 –35 9.2 –45 MCLKOUT (MHz) 10.4 Figure 18. MCLKOUT vs. Temperature for Various Supplies Rev.
PAGE 12
AD7400A Data Sheet TERMINOLOGY Differential Nonlinearity Differential nonlinearity is the difference between the measured and the ideal 1 LSB change between any two adjacent codes in the ADC. Integral Nonlinearity Integral nonlinearity is the maximum deviation from a straight line passing through the endpoints of the ADC transfer function.
PAGE 13
Data Sheet AD7400A THEORY OF OPERATION CIRCUIT INFORMATION The AD7400A isolated Σ-Δ modulator converts an analog input signal into a high speed (10 MHz typical), single-bit data stream; the time average of the single-bit data from the modulator is directly proportional to the input signal.
PAGE 14
AD7400A Data Sheet DIFFERENTIAL INPUTS The analog input to the modulator is a switched capacitor design. The analog signal is converted into charge by highly linear sampling capacitors. A simplified equivalent circuit diagram of the analog input is shown in Figure 22. A signal source driving the analog input must be able to provide the charge onto the sampling capacitors every half MCLKOUT cycle and settle to the required accuracy within the next half cycle.
PAGE 15
Data Sheet AD7400A DIGITAL FILTER reg [23:0] diff2; The overall system resolution and throughput rate is determined by the filter selected and the decimation rate used. The higher the decimation rate, the greater the system accuracy, as illustrated in Figure 24. However, there is a tradeoff between accuracy and throughput rate and, therefore, higher decimaltion rates result in lower throughput solutions.
PAGE 16
AD7400A Data Sheet /*DIFFERENTIATOR (including decimation stage) Perform the differentiation stage (FIR) at a lower speed. DIFF1 – + – Z–1 DIFF3 WORD_CLK Z–1 DIFF3 07077-022 Z–1 + DIFF2 – /* Clock the Sinc output into an output register WORD_CLK Figure 26.
PAGE 17
Data Sheet AD7400A APPLICATIONS INFORMATION GROUNDING AND LAYOUT INSULATION LIFETIME Supply decoupling with a value of 100 nF is strongly recommended on both VDD1 and VDD2. Decoupling on one or both VDDx pins does not significantly affect performance. In applications involving high common-mode transients, ensure that board coupling across the isolation barrier is minimized.
PAGE 18
AD7400A Data Sheet OUTLINE DIMENSIONS 10.50 (0.4134) 10.10 (0.3976) 9 16 7.60 (0.2992) 7.40 (0.2913) 8 1.27 (0.0500) BSC 0.30 (0.0118) 0.10 (0.0039) COPLANARITY 0.10 0.51 (0.0201) 0.31 (0.0122) 10.65 (0.4193) 10.00 (0.3937) 0.75 (0.0295) 45° 0.25 (0.0098) 2.65 (0.1043) 2.35 (0.0925) SEATING PLANE 8° 0° 0.33 (0.0130) 0.20 (0.0079) 1.27 (0.0500) 0.40 (0.
PAGE 19
Data Sheet AD7400A NOTES Rev.