Datasheet AD7472, AD7470 Datasheet (Analog Devices)

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Information furnished by Analog Devices is believed to be accurate and reliable. However, no responsibility is assumed by Analog Devices for its use, nor for any infringements of patents or other rights of third parties which may result from its use. No license is granted by implication or otherwise under any patent or patent rights of Analog Devices.

AD7470/AD7472

One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A. Tel: 781/329-4700 World Wide Web Site: http://www.analog.com Fax: 781/326-8703 © Analog Devices, Inc., 2000

1.75 MSPS, 4 mW

10-Bit/12-Bit Parallel ADCs

FUNCTIONAL BLOCK DIAGRAM

T/H

10-/12-BIT

SUCCESSIVE

APPROXIMATION

ADC

OUTPUT

DRIVERS

AD7470/AD7472

CONVST

AGND DGND

DDDVDD

REF IN

DRIVE

DB9 (DB11)

DB0

CLK IN

BUSY

CONTROL

LOGIC

AD7470 IS A 10-BIT PART WITH DB0 TO DB9 AS OUTPUTS. AD7472 IS A 12-BIT PART WITH DB0 TO DB11 AS OUTPUTS.

FEATURES Specified for V

of 2.7 V to 5.25 V

1.75 MSPS for AD7470 (10-Bit)

1.5 MSPS for AD7472 (12-Bit) Low Power

AD7470: 3.34 mW Typ at 1.5 MSPS with 3 V Supplies

7.97 mW Typ at 1.75 MSPS with 5 V Supplies

AD7472: 3.54 mW Typ at 1.2 MSPS with 3 V Supplies

8.7 mW Typ at 1.5 MSPS with 5 V Supplies Wide Input Bandwidth 70 dB Typ SNR at 500 kHz Input Frequency Flexible Power/Throughput Rate Management No Pipeline Delays High Speed Parallel Interface Sleep Mode: 50 nA Typ 24-Lead SOIC and TSSOP Packages

GENERAL DESCRIPTION

The AD7470/AD7472 are 10-bit/12-bit high speed, low power, successive-approximation ADCs. The parts operate from a single 2.7 V to 5.25 V power supply and feature throughput rates up to 1.5 MSPS for the 12-bit AD7472 and up to 1.75 MSPS for the 10-bit AD7470. The parts contain a low noise, wide bandwidth track/hold amplifier that can handle input frequencies in excess of 1 MHz.

The conversion process and data acquisition are controlled using standard control inputs allowing easy interfacing to microprocessors or DSPs. The input signal is sampled on the falling edge of CONVST and conversion is also initiated at this point. The BUSY goes high at the start of conversion and goes low 531.66 ns after falling edge of CONVST (AD7472 with a clock frequency of 26 MHz) to indicate that the conversion is complete. There are no pipelined delays associated with the part. The conversion result is accessed via standard CS and RD sig- nals over a high speed parallel interface.

The AD7470/AD7472 uses advanced design techniques to achieve very low power dissipation at high throughput rates. With 3 V supplies and 1.5 MSPS throughput rate, the AD7470 typically consumes, on average, just 1.1 mA. With 5 V supplies and

1.75 MSPS, the average current consumption is typically

1.6 mA. The part also offers flexible power/throughput rate management. Operating the AD7470 with 3 V supplies and 500 kSPS throughput reduces the current consumption to 713 µA. At 5 V supplies and 500 kSPS, the part consumes 944 µA.

It is also possible to operate the parts in an auto sleep mode, where the part wakes up to do a conversion and automatically enters sleep mode at the end of conversion. Using this method allows very low power dissipation numbers at lower throughput rates. In this mode, the AD7472 can be operated with 3 V supplies at 100 kSPS, and consume an average current of just 124 µA. At 5 V supplies and 100 kSPS, the average current consumption is 171 µA.

The analog input range for the part is 0 to REF IN. The +2.5 V reference is applied externally to the REF IN pin. The conversion rate is determined by the externally-applied clock.

PRODUCT HIGHLIGHTS

1. High Throughput with Low Power Consumption. The AD7470 offers 1.75 MSPS throughput and the AD7472 offers 1.5 MSPS throughput rates with 4 mW power consumption.

2. Flexible Power/Throughput Rate Management. The conversion rate is determined by an externally-applied clock allowing the power to be reduced as the conversion rate is reduced. The part also features an auto sleep mode to maximize power efficiency at lower throughput rates.

3. No Pipeline Delay. The part features a standard successiveapproximation ADC with accurate control of the sampling instant via a CONVST input and once off conversion control.

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AD7470/AD7472

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AD7470–SPECIFICATIONS

(VDD = +2.7 V to +5.25 V2, REF IN = 2.5 V, f

CLK IN

= 30 MHz @ 5 V and 24 MHz @ 3 V;

TA = T

MIN

to T

MAX

, unless otherwise noted.)

Parameter A Version

Units Test Conditions/Comments

DYNAMIC PERFORMANCE 5 V 3 V f

= 1.75 MSPS @ 5 V, fS = 1.5 MSPS @ 3 V

Signal to Noise + Distortion (SINAD) 60 60 dB min fIN = 500 kHz Sine Wave

60 60 fIN = 100 kHz Sine Wave

Signal-to-Noise Ratio (SNR) 60 60 dB min fIN = 500 kHz Sine Wave

60 60 fIN = 100 kHz Sine Wave

Total Harmonic Distortion (THD) –83 –83 dB typ f

= 500 kHz Sine Wave

–75 –75 dB max fIN = 100 kHz Sine Wave

Peak Harmonic or Spurious Noise (SFDR) –85 –85 dB typ fIN = 500 kHz Sine Wave

–75 –75 dB max f

= 100 kHz Sine Wave

Intermodulation Distortion (IMD)

Second Order Terms –79 –75 dB typ fIN = 500 kHz Sine Wave

–75 –75 dB max fIN = 100 kHz Sine Wave

Third Order Terms –77 –75 dB typ fIN = 500 kHz Sine Wave

–75 –75 dB max fIN = 100 kHz Sine Wave Aperture Delay 5 5 ns typ Aperture Jitter 15 15 ps typ Full Power Bandwidth 20 20 MHz typ

DC ACCURACY fS = 1.75 MSPS @ 5 V; fS = 1.5 MSPS @ 3 V

Resolution 10 10 Bits Integral Nonlinearity ± 1 ±1 LSB max Differential Nonlinearity ± 0.9 ±0.9 LSB max Guaranteed No Missed Codes to 10 Bits Offset Error ± 2.5 ±2.5 LSB max Gain Error ± 1 ±1 LSB max

ANALOG INPUT

Input Voltage Ranges 0 to REF IN 0 to REF IN V DC Leakage Current ±1 ±1 µA max Input Capacitance 33 33 pF typ

REFERENCE INPUT

REF IN Input Voltage Range 2.5 2.5 V ± 1% for Specified Performance DC Leakage Current ±1 ±1 µA max Input Capacitance 10/20 10/20 pF typ Track/Hold Mode

LOGIC INPUTS

Input High Voltage, V

INH

2.4 2.4 V min

Input Low Voltage, V

INL

0.4 0.4 V max

Input Current, I

± 1 ±1 µA max Typically 10 nA, VIN = 0 V or V

Input Capacitance, C

10 10 pF max

LOGIC OUTPUTS

Output High Voltage, V

DRIVE

– 0.2 V

DRIVE

– 0.2 V min I

SOURCE

= 200 µA

Output Low Voltage, V

0.4 0.4 V max I

SINK

= 200 µA Floating-State Leakage Current ± 10 ± 10 µA max VDD = 2.7 V to 5.25 V Floating-State Output Capacitance 10 10 pF max Output Coding Straight (Natural) Binary

CONVERSION RATE

Conversion Time 12 12 CLK IN Cycles (max) Track/Hold Acquisition Time 135 135 ns min Throughput Rate 1.75 1.5 MSPS max Conversion Time + Acquisition Time

CLK IN of 30 MHz @ 5 V and 24 MHz @ 3 V

POWER REQUIREMENTS

+2.7/+5.25 V min/max

Digital I/Ps = 0 V or DV

Normal Mode 2.4 mA max VDD = 4.75 V to 5.25 V; fS = 1.75 MSPS; Typ 2 mA Quiescent Current 900 µA max VDD = 4.75 V to 5.25 V; fS = 1.75 MSPS Normal Mode 1.5 mA max VDD = 2.7 V to 3.3 V; fS = 1.5 MSPS; Typ 1.3 mA Quiescent Current 800 µA max VDD = 2.7 V to 3.3 V; fS = 1.5 MSPS Sleep Mode 1 µA max CLK IN = 0 V or DV

Power Dissipation

Digital I/Ps = 0 V or DV

Normal Mode 12 mW max VDD = 5 V

4.5 mW max VDD = 3 V

Sleep Mode 5 µW max VDD = 5 V; CLK IN = 0 V or DV

3 µW max VDD = 3 V; CLK IN = 0 V or DV

NOTES

Temperature ranges as follows: A Version: -40°C to +85°C.

The AD7470 functionally works at 2.35 V. Typical specifications @ +25°C for SNR (100 kHz) = 59 dB; THD (100 kHz) = –84 dB; INL ± 0.8 LSB.

The AD7470 will typically maintain A-grade performance up to +125°C, with a reduced CLK of 20 MHz @ 5 V and 16 MHz @ 3 V. Typical Sleep Mode current @ +125°C is 700 nA.

Sample tested @ +25°C to ensure compliance.

See Power vs. Throughput Rate section.

Specifications subject to change without notice.

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AD7470/AD7472

AD7472–SPECIFICATIONS

(VDD = +2.7 V to +5.25 V2, REF IN = 2.5 V, f

CLK IN

= 26 MHz @ 5 V and 20 MHz @ 3 V;

TA = T

MIN

to T

MAX

, unless otherwise noted.)

Parameter A Version

B Version

Units Test Conditions/Comments

DYNAMIC PERFORMANCE 5 V3 V 5 V3 V f

= 1.5 MSPS @ 5 V, fS = 1.2 MSPS @ 3 V

Signal to Noise + Distortion (SINAD) 69 69 69 69 dB typ fIN = 500 kHz Sine Wave

68 68 68 68 dB min f

= 100 kHz Sine Wave

Signal-to-Noise Ratio (SNR) 70 70 70 70 dB typ f

= 500 kHz Sine Wave

68 68 68 68 dB min fIN = 100 kHz Sine Wave

Total Harmonic Distortion (THD) –83 –78 –83 –78 dB typ fIN = 500 kHz Sine Wave

–83 –84 –83 –84 dB typ f

= 100 kHz Sine Wave

–75 –75 –75 –75 dB max f

= 100 kHz Sine Wave

Peak Harmonic or Spurious Noise

(SFDR) –86 –81 –86 –81 dB typ fIN = 500 kHz Sine Wave

–86 –86 –86 –86 dB typ fIN = 100 kHz Sine Wave –76 –76 –76 –76 dB max fIN = 100 kHz Sine Wave

Intermodulation Distortion (IMD)

Second Order Terms –77 –77 –77 –77 dB typ fIN = 500 kHz Sine Wave

–86 –86 –86 –86 dB typ fIN = 100 kHz Sine Wave

Third Order Terms –77 –77 –77 –77 dB typ fIN = 500 kHz Sine Wave

–86 –86 –86 –86 dB typ fIN = 100 kHz Sine Wave Aperture Delay 5 5 5 5 ns typ Aperture Jitter 15 15 15 15 ps typ Full Power Bandwidth 20 20 20 20 MHz typ

DC ACCURACY fS = 1.5 MSPS @ 5 V; fS = 1.2 MSPS @ 3 V

Resolution 12 12 12 12 Bits Integral Nonlinearity ± 2 ± 2 ± 1 ± 1 LSB max Guaranteed No Missed Codes to 11 Bits

(A Version)

Differential Nonlinearity ± 1.8 ±1.8 ± 0.9 ± 0.9 LSB max Guaranteed No Missed Codes to 12 Bits

(B Version) Offset Error ± 10 ±10 ± 10 ±10 LSB max Gain Error ± 2 ± 2 ± 2 ± 2 LSB max

ANALOG INPUT

Input Voltage Ranges 0 to REF IN 0 to REF IN 0 to REF IN 0 to REF IN V DC Leakage Current ±1 ± 1 ±1 ±1 µA max Input Capacitance 33 33 33 33 pF typ

REFERENCE INPUT

REF IN Input Voltage Range 2.5 2.5 2.5 2.5 V ± 1% for Specified Performance DC Leakage Current ± 1 ± 1 ±1 ±1 µA max Input Capacitance 10/20 10/20 10/20 10/20 pF typ Track/Hold Mode

LOGIC INPUTS

Input High Voltage, V

INH

2.4 2.4 2.4 2.4 V min

Input Low Voltage, V

INL

0.4 0.4 0.4 0.4 V max

Input Current, I

±1 ±1 ± 1 ±1 µA max Typically 10 nA, VIN = 0 V or V

Input Capacitance, C

10 10 10 10 pF max

LOGIC OUTPUTS

Output High Voltage, V

DRIVE

– 0.2 V

DRIVE

– 0.2 V

DRIVE

– 0.2 V

DRIVE

– 0.2 V min I

SOURCE

= 200 µA

Output Low Voltage, V

0.4 0.4 0.4 0.4 V max I

SINK

= 200 µA Floating-State Leakage Current ±10 ±10 ±10 ± 10 µA max VDD = 2.7 V to 5.25 V Floating-State Output Capacitance 10 10 10 10 pF max Output Coding Straight (Natural) Binary Straight (Natural) Binary

CONVERSION RATE

Conversion Time 14 14 14 14 CLK IN

Cycles (max) Track/Hold Acquisition Time 135 135 135 135 ns min Throughput Rate 1.5 1.2 1.5 1.2 MSPS max Conversion Time + Acquisition Time

CLK IN Is 26 MHz @ 5 V and 20 MHz @ 3 V

POWER REQUIREMENTS

+2.7/+5.25 +2.7/+5.25 V min/max

Digital I/Ps = 0 V or DV

Normal Mode 2.4 2.4 mA max VDD = 4.75 V to 5.25 V; fS = 1.5 MSPS; Typ 2 mA Quiescent Current 900 900 µA max VDD = 4.75 V to 5.25 V; fS = 1.5 MSPS Normal Mode 1.5 1.5 mA max VDD = 2.7 V to 3.3 V; fS = 1.2 MSPS; Typ 1.3 mA Quiescent Current 800 800 µAV

= 2.7 V to 3.3 V; fS = 1.2 MSPS

Sleep Mode 1 1 µA max CLK IN = 0 V or DV

Power Dissipation

Digital I/Ps = 0 V or DV

Normal Mode 12 12 mW max VDD = 5 V

4.5 4.5 mW max VDD = 3 V

Sleep Mode 5 5 µW max VDD = 5 V; CLK IN = 0 V or DV

33µW max VDD = 3 V; CLK IN = 0 V or DV

NOTES

Temperature ranges as follows: A and B Versions: –40°C to +85°C.

The AD7472 functionally works at 2.35 V. Typical specifications @ +25°C for SNR (100 kHz) = 68 dB; THD (100 kHz) = –84 dB; INL ± 0.8 LSB.

The AD7472 will typically maintain A-grade performance up to +125°C, with a reduced CLK of 18 MHz @ 5 V and 14 MHz @ 3 V. Typical Sleep Mode current @ +125°C is 700 nA.

Sample tested @ +25°C to ensure compliance.

See Power vs. Throughput Rate section.

Specifications subject to change without notice.

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Limit at T

MIN

, T

MAX

Parameter AD7470 AD7472 Units Description

CLK

10 10 kHz min 30 26 MHz max

CONVERT

436.42 531.66 ns min t

CLK

= 1/f

CLK IN

WAKEUP

11µs max Wake-Up Time

10 10 ns min CONVST Pulsewidth

10 10 ns max CONVST to BUSY Delay, VDD = 5 V 30 30 ns max CONVST to BUSY Delay, V

= 3 V

0 0 ns max BUSY to CS Setup Time

0 0 ns max CS to RD Setup Time

20 20 ns min RD Pulsewidth

15 15 ns min Data Access Time After Falling Edge of RD

8 8 ns max Bus Relinquish Time After Rising Edge of RD

0 0 ns max CS to RD Hold Time

135 135 ns min Acquisition Time

100 100 ns min Quiet Time

NOTES

Sample tested at +25°C to ensure compliance. All input signals are specified with tr = tf = 5 ns (10% to 90% of VDD) and timed from a voltage level of 1.6 V. See Figure 1.

Mark/Space ratio for the CLK input is 40/60 to 60/40. First CLK pulse should be 10 ns min from falling edge of CONVST.

t2 is 35 ns max @ +125°C.

Measured with the load circuit of Figure 1 and defined as the time required for the output to cross 0.8 V or 2.0 V.

t7 is derived from the measured time taken by the data outputs to change 0.5 V when loaded with the circuit of Figure 1. The measured number is then extrapolated back to remove the effects of charging or discharging the 50 pF capacitor. This means that the time, t

, quoted in the timing characteristics is the true bus relinquish

time of the part and is independent of the bus loading.

Specifications subject to change without notice.

TIMING SPECIFICATIONS

(VDD = +2.7 V to +5.25 V, REF IN = 2.5 V; TA = T

MIN

to T

MAX

, unless otherwise noted.)

200␮A

50pF

TO OUTPUT

+1.6V

Figure 1. Load Circuit for Digital Output Timing Specifications

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CAUTION

ESD (electrostatic discharge) sensitive device. Electrostatic charges as high as 4000 V readily accumulate on the human body and test equipment and can discharge without detection. Although the AD7470/AD7472 features proprietary ESD protection circuitry, permanent damage may occur on devices subjected to high energy electrostatic discharges. Therefore, proper ESD precautions are recommended to avoid performance degradation or loss of functionality.

WARNING!

ESD SENSITIVE DEVICE

ABSOLUTE MAXIMUM RATINGS

(TA = +25°C unless otherwise noted)

to AGND/DGND . . . . . . . . . . . . . . . . . –0.3 V to +7 V

DRIVE

to AGND/DGND . . . . . . . . . . . . . . . . –0.3 V to +7 V

to DVDD . . . . . . . . . . . . . . . . . . . . . . .–0.3 V to +0.3 V

DRIVE

to DVDD . . . . . . . . . . . . . . . –0.3 V to DVDD + 0.3 V

AGND TO DGND . . . . . . . . . . . . . . . . . . . . –0.3 V to +0.3 V

Analog Input Voltage to AGND . . . –0.3 V to AVDD + 0.3 V Digital Input Voltage to DGND . . . –0.3 V to DVDD + 0.3 V

REF IN to AGND . . . . . . . . . . . . . . –0.3 V to AVDD + 0.3 V

Input Current to Any Pin Except Supplies

. . . . . . . . ± 10 mA

Operating Temperature Range

Commercial (A and B Version) . . . . . . . . . –40°C to +85°C

Storage Temperature Range . . . . . . . . . . . –65°C to +150°C

Junction Temperature . . . . . . . . . . . . . . . . . . . . . . . . .+150°C

SOIC, TSSOP Package Dissipation . . . . . . . . . . . . . +450 mW

Thermal Impedance . . . . . . . . . . . . . . . 75°C/W (SOIC)

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .115°C/W (TSSOP)

Thermal Impedance . . . . . . . . . . . . . . . 25°C/W (SOIC)

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .35°C/W (TSSOP)

Lead Temperature, Soldering

Vapor Phase (60 secs) . . . . . . . . . . . . . . . . . . . . . . .+215°C

Infrared (15 secs) . . . . . . . . . . . . . . . . . . . . . . . . . . .+220°C

NOTES

Stresses above those listed under Absolute Maximum Ratings may cause perma-

nent damage to the device. This is a stress rating only; functional operation of the device at these or any other conditions above those listed in the operational sections of this specification is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability.

Transient currents of up to 100 mA will not cause SCR latch-up.

ORDERING GUIDE

Temperature Resolution Package

Model Range (Bits) Options

AD7470ARU –40°C to +85°C 10 RU-24 AD7472AR –40°C to +85°C 12 R-24 AD7472BR –40°C to +85°C 12 R-24 AD7472ARU –40°C to +85°C 12 RU-24 AD7472BRU –40°C to +85°C 12 RU-24 EVAL-AD7470CB

Evaluation Board

EVAL-AD7472CB

Evaluation Board

EVAL-CONTROL BOARD

Controller Board

HSC-INTERFACE BOARD Evaluation High Speed Interface Board

NOTES

R = SOIC; RU = TSSOP.

This can be used as a stand-alone evaluation board or in conjunction with the EVAL-CONTROL BOARD for evaluation/demonstration purposes.

This board is a complete unit allowing a PC to control and communicate with all Analog Devices evaluation boards ending in the CB designators.

PIN CONFIGURATIONS

TOP VIEW

(Not to Scale)

AD7470

NC = NO CONNECT

DB7 DB6

DB8 DB5

(MSB) DB9 DB4

DRIVE

REF IN DV

DGND

AGND DB3

DB2

DB1

CONVST

DB0 (LSB)

CLKIN NC

BUSY NC

TOP VIEW

(Not to Scale)

AD7472

DB9 DB8

DB10 DB7

(MSB) DB11 DB6

DRIVE

REF IN DV

DGND

AGND DB5

DB4

DB3

CONVST

DB2

CLKIN DB1

BUSY DB0 (LSB)

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PIN FUNCTION DESCRIPTION

Pin Mnemonic Function

CS Chip Select. Active low logic input used in conjunction with RD to access the conversion result. The conversion

result is placed on the data bus following the falling edge of both CS and RD. CS and RD are both connected to the same AND gate on the input so the signals are interchangeable. CS can be hardwired permanently low.

RD Read Input. Logic Input used in conjunction with CS to access the conversion result. The conversion result is

placed on the data bus following the falling edge of both CS and RD. CS and RD are both connected to same AND gate on the input so the signals are interchangeable. CS and RD can be hardwired permanently low in which case, the data bus is always active and the result of the new conversion is clocked out slightly before to the BUSY line going low.

CONVST Conversion Start Input. Logic Input used to initiate conversion. The input track/hold amplifier goes from track

mode to hold mode on the falling edge of CONVST and the conversion process is initiated at this point. The conversion input can be as narrow as 15 ns. If the CONVST input is kept low for the duration of conversion and is still low at the end of conversion, the part will automatically enter sleep mode. If the part enters this sleep mode, the next rising edge of CONVST wakes up the part. Wake-up time for the part is typically 1 µs.

CLK IN Master Clock Input. The clock source for the conversion process is applied to this pin. Conversion time for the

AD7472 takes 14 clock cycles while conversion time for the AD7470 takes 12 clock cycles. The frequency of this master clock input, therefore, determines the conversion time and achievable throughput rate. While the ADC is not converting, the Clock-In pad is in three-state and thus no clock is going through the part.

BUSY BUSY Output. Logic Output indicating the status of the conversion process. The BUSY signal goes high after the

falling edge of CONVST and stays high for the duration of conversion. Once conversion is complete and the conversion result is in the output register, the BUSY line returns low. The track/hold returns to track mode just prior to the falling edge of BUSY and the acquisition time for the part begins when BUSY goes low. If the CONVST input is still low when BUSY goes low, the part automatically enters its sleep mode on the falling edge of BUSY.

REF IN Reference Input. An external reference must be applied to this input. The voltage range for the external reference

is 2.5 V ± 1% for specified performance.

Analog Supply Voltage, +2.7 V to +5.25 V. This is the only supply voltage for all analog circuitry on the AD7470/ AD7472. The AV

and DV

voltages should ideally be at the same potential and must not be more than 0.3 V

apart even on a transient basis. This supply should be decoupled to AGND.

Digital Supply Voltage, +2.7 V to +5.25 V. This is the supply voltage for all digital circuitry on the AD7470/ AD7472 apart from the output drivers. The DV

and AV

voltages should ideally be at the same potential and

must not be more than 0.3 V apart even on a transient basis. This supply should be decoupled to DGND.

AGND Analog Ground. Ground reference point for all analog circuitry on the AD7470/AD7472. All analog input signals

and any external reference signal should be referred to this AGND voltage. The AGND and DGND voltages should ideally be at the same potential and must not be more than 0.3 V apart even on a transient basis.

DGND Digital Ground. This is the ground reference point for all digital circuitry on the AD7470 and AD7472. The

DGND and AGND voltages should ideally be at the same potential and must not be more than 0.3 V apart even on a transient basis.

Analog Input. Single-ended analog input channel. The input range is 0 V to REFIN. The analog input presents a high dc input impedance.

DRIVE

Supply Voltage for the Output Drivers, +2.7 V to +5.25 V. This voltage determines the output high voltage for the data output pins. It allows the AV

and DVDD to operate at 5 V (and maximize the dynamic performance of the

ADC) while the digital outputs can interface to 3 V logic.

DB0–DB9/11 Data Bit 0 to Data Bit 9 (AD7470) and DB11 (AD7472). Parallel digital outputs that provide the conversion

result for the part. These are three-state outputs that are controlled by CS and RD. The output high voltage level for these outputs is determined by the V

DRIVE

input.

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TERMINOLOGY Integral Nonlinearity

This is the maximum deviation from a straight line passing through the endpoints of the ADC transfer function. The endpoints of the transfer function are zero scale, a point 1/2 LSB below the first code transition, and full scale, a point 1/2 LSB above the last code transition.

Differential Nonlinearity

This is the difference between the measured and the ideal 1 LSB change between any two adjacent codes in the ADC.

Offset Error

This is the deviation of the first code transition (00 . . . 000) to (00 . . . 001) from the ideal, i.e., AGND + 1 LSB.

Gain Error

The last transition should occur at the analog value 1 1/2 LSB below the nominal full scale. The first transition is a 1/2 LSB above the low end of the scale (zero in the case of AD7470/ AD7472). The gain error is the deviation of the actual difference between the first and last code transitions from the ideal difference between the first and last code transitions with offset errors removed.

Track/Hold Acquisition Time

The track/hold amplifier returns into track mode after the end of conversion. Track/Hold acquisition time is the time required for the output of the track/hold amplifier to reach its final value, within ± 1 LSB, after the end of conversion.

Signal to (Noise + Distortion) Ratio

This is the measured ratio of signal to (noise + distortion) at the output of the A/D converter. The signal is the rms amplitude of the fundamental. Noise is the sum of all nonfundamental signals up to half the sampling frequency (f

/2), excluding dc. The ratio is dependent on the number of quantization levels in the digitization process; the more levels, the smaller the quantization noise. The theoretical signal to (noise + distortion) ratio for an ideal N-bit converter with a sine wave input is given by:

Signal to (Noise + Distortion) = (6.02 N + 1.76) dB

Thus for a 12-bit converter, this is 74 dB and for a 10-bit converter is 62 dB.

Total Harmonic Distortion

Total harmonic distortion (THD) is the ratio of the rms sum of harmonics to the fundamental. For the AD7470/AD7472 it is defined as:

THD dB

VVVVV

( ) log

()

++++

223242526

where V1 is the rms amplitude of the fundamental and V2, V3,

, V5 and V6 are the rms amplitudes of the second through the

sixth harmonics.

Peak Harmonic or Spurious Noise

Peak harmonic or spurious noise is defined as the ratio of the rms value of the next largest component in the ADC output spectrum (up to f

/2 and excluding dc) to the rms value of the fundamental. Normally, the value of this specification is determined by the largest harmonic in the spectrum, but for ADCs where the harmonics are buried in the noise floor, it will be a noise peak.

Intermodulation Distortion

With inputs consisting of sine waves at two frequencies, fa and fb, any active device with nonlinearities will create distortion products at sum and difference frequencies of mfa ± nfb where m, n = 0, 1, 2, 3, etc. Intermodulation distortion terms are those for which neither m nor n is equal to zero. For example, the second order terms include (fa + fb) and (fa – fb), while the third order terms include (2fa + fb), (2fa – fb), (fa + 2fb) and (fa – 2fb).

The AD7470/AD7472 are tested using the CCIF standard where two input frequencies near the top end of the input bandwidth are used. In this case, the second order terms are usually distanced in frequency from the original sine waves while the third order terms are usually at a frequency close to the input frequencies. As a result, the second and third order terms are specified separately. The calculation of the intermodulation distortion is as per the THD specification where it is the ratio of the rms sum of the individual distortion products to the rms amplitude of the sum of the fundamentals expressed in dBs.

Aperture Delay

In a sample/hold, the time required after the hold command for the switch to open fully is the aperture delay. The sample is, in effect, delayed by this interval, and the hold command would have to be advanced by this amount for precise timing.

Aperture Jitter

Aperture jitter is the range of variation in the aperture delay. In other words, it is the uncertainty about when the sample is taken. Jitter is the result of noise which modulates the phase of the hold command. This specification establishes the ultimate timing error, hence the maximum sampling frequency for a given resolution. This error will increase as the input dV/dt increases.

Page 8

REV. A

AD7470/AD7472

–8–

CIRCUIT DESCRIPTION CONVERTER OPERATION

The AD7470/AD7472 is a 10-bit/12-bit successive approximation analog-to-digital converter based around a capacitive DAC. The AD7470/AD7472 can convert analog input signals in the range 0 V to V

REF

. Figure 2 shows a very simplified schematic of the ADC. The Control Logic, SAR and the Capacitive DAC are used to add and subtract fixed amounts of charge from the sampling capacitor to bring the comparator back into a balanced condition.

CAPACITIVE

DAC

SWITCHES

SAR

CONTROL LOGIC

COMPARATOR

OUTPUT DATA 10-/12-BIT PARALLEL

REF

CONTROL

INPUTS

Figure 2. Simplified Block Diagram of AD7470/AD7472

Figure 3 shows the ADC during its acquisition phase. SW2 is closed and SW1 is in Position A. The comparator is held in a balanced condition and the sampling capacitor acquires the signal on V

COMPARATOR

CONTROL LOGIC

CAPACITIVE

DAC

AGND

2k⍀

SW2

SW1

Figure 3. ADC Acquisition Phase

Figure 4 shows the ADC during conversion. When conversion starts SW2 will open and SW1 will move to position B, causing the comparator to become unbalanced. The ADC then runs through its successive approximation routine and brings the comparator back into a balanced condition. When the comparator is rebalanced, the conversion result is available in the SAR register.

COMPARATOR

CONTROL LOGIC

CAPACITIVE

DAC

AGND

2k⍀

SW2

SW1AB

Figure 4. ADC Conversion Phase

TYPICAL CONNECTION DIAGRAM

Figure 5 shows a typical connection diagram for the AD7470/ AD7472. Conversion is initiated by a falling edge on CONVST. Once CONVST goes low the BUSY signal goes high, and at the end of conversion the falling edge of BUSY is used to activate an Interrupt Service Routine. The CS and RD lines are then activated in parallel to read the 10- or 12-data bits. The recommended REF IN voltage is 2.5 V providing an analog input range of 0 V to 2.5 V, making the AD7470/AD7472 a unipolar A/D. It is recommended to perform a dummy conversion after power-up as the first conversion result could be incorrect. This also ensures that the part is in the correct mode of operation. The CONVST pin should not be floating when power is applied as a rising edge on CONVST might not wake up the part.

In Figure 5 the V

DRIVE

pin is tied to DVDD, which results in logic

output voltage values being either 0 V or DV

. The voltage

applied to V

DRIVE

controls the voltage value of the output logic

signals. For example, if DV

is supplied by a 5 V supply and

DRIVE

by a 3 V supply, the logic output voltage levels would be either 0 V or 3 V. This feature allows the AD7470/AD7472 to interface to 3 V parts while still enabling the A/D to process signals at 5 V supply.

10␮F0.1␮F

PARALLED

INTERFACE

+2.5V*

*RECOMMENDED REF IN VOLTAGE

0V TO REF IN

1nF

10␮F 0.1␮F 47␮F

AD7470/

AD7472

DRIVE

REF IN

DB0– DB9 (DB11)

BUSY

CONVST RD

␮C/␮P

ANALOG SUPPLY

2.7V–5.25V

Figure 5. Typical Connection Diagram

Page 9

REV. A

AD7470/AD7472

–9–

ADC TRANSFER FUNCTION

The output coding of the AD7470/AD7472 is straight binary. The designed code transitions occur at successive integer LSB values (i.e., 1 LSB, 2 LSB, etc.). The LSB size is = (REF IN)/ 4096 for the AD7472 and (REF IN)/1024 for the AD7470. The ideal transfer characteristic for the AD7472 is shown in Figure 6.

111...111

111...110

111...000

011...111

000...010

000...001

000...000

ADC CODE

0V 1/2LSB +V

REF

–1LSB

ANALOG INPUT

1LSB = V

REF

/4096

Figure 6. Transfer Characteristic for 12 Bits

AC ACQUISITION TIME

In ac applications it is recommended to always buffer analog input signals. The source impedance of the drive circuitry must be kept as low as possible to minimize the acquisition time of the ADC. Large values of impedance at the VIN pin of the ADC will cause the THD to degrade at high input frequencies.

TYPICAL AMPLIFIER INPUT SNR THD CURRENT BUFFERS 500kHz 500kHz CONSUMPTION

AD8047 70 78 5.8mA

AD9631 69.5 80 17mA

AD8051 68.6 78 4.4mA

AD797 70 84 8.2mA

AD7470/AD7472

DYNAMIC

PERFORMANCE

SPECIFICATIONS

Figure 7. Recommended Input Buffers

Reference Input

The following references are best suited for use with the AD7470/AD7472.

ADR291 AD780 AD192

For optimum performance, a 2.5 V reference is recommended. The part can function with a reference up to 3 V and down to 2 V, but the performance deteriorates.

DC Acquisition Time

The ADC starts a new acquisition phase at the end of a conversion and ends it on the falling edge of the CONVST signal. At the end of conversion there is a settling time associated with the sampling circuit. This settling time lasts approximately 135 ns. The analog signal on V

is also being acquired during this settling time; therefore, the minimum acquisition time needed is approximately 135 ns.

Figure 8 shows the equivalent charging circuit for the sampling capacitor when the ADC is in its acquisition phase. R3 represents the source impedance of a buffer amplifier or resistive network, R1 is an internal switch resistance, R2 is for bandwidth control and C1 is the sampling capacitor. C2 is back-plate capacitance and switch parasitic capacitance.

During the acquisition phase the sampling capacitor must be charged to within 1 LSB of its final value.

125⍀

22pF

8pF

R2 636⍀

Figure 8. Equivalent Sampling Circuit

ANALOG INPUT

Figure 9 shows the equivalent circuit of the analog input structure of the AD7470/AD7472. The two diodes, D1 and D2, provide ESD protection for the analog inputs. The capacitor C3 is typically about 4 pF and can be primarily attributed to pin capacitance. The resistor R1 is an internal switch resistance. This resistor is typically about 125 Ω. The capacitor C1 is the sampling capacitor while R2 is used for bandwidth control.

125⍀

22pF

8pF

636⍀

4pF

Figure 9. Equivalent Analog Input Circuit

CLOCK SOURCES

The max CLK specification for the AD7470 is 30 MHz and for the AD7472, it is 26 MHz. These frequencies are not standard off-the-shelf oscillator frequencies. Many manufacturers produce oscillator modules close to these frequencies; a typical one being 25.175 MHz from IQD Limited. AEL Crystals Limited produce a 25 MHz oscillator module in various packages. Crystal oscillator manufacturers will produce 26 MHz and 30 MHz oscillators to order. Of course any clock source can be used, not just crystal oscillators.

Page 10

REV. A

AD7470/AD7472

–10–

PARALLEL INTERFACE

The parallel interface of the AD7470 and AD7472 is 10-bits and 12-bits wide respectively. The output data buffers are activated when both CS and RD are logic low. At this point the contents of the data register are placed onto the data bus. Figure 10 shows the timing diagram for the parallel port.

Figure 11 shows the timing diagram for the parallel port when CS and RD are tied permanently low. In this setup, once the BUSY line goes from high to low the conversion process is

completed. The data is available on the output bus slightly before the falling edge of BUSY.

It is important to point out that data bus cannot change state while the A/D is doing a conversion as this would have a detrimental effect on the conversion in progress. The data out lines will go three-state again when either the RD or CS line goes high. Thus the CS can be tied low permanently, leaving the RD line to control conversion result access. Please reference the V

DRIVE

section for output voltage levels.

CONVERT

BUSY

DBx

CONVST*

*CONVST SHOULD GO HIGH WHEN THE CLK IS HIGH OR BEFORE THE FIRST CLK CYCLE.

Figure 10. Parallel Port Timing

CONVERT

CONVST*

BUSY

DBx

DATA N DATA N+1

*CONVST SHOULD GO HIGH WHEN THE CLK IS HIGH OR BEFORE THE FIRST CLK CYCLE.

Figure 11. Parallel Port Timing with CS and RD Tied Low

CLK IN

CONVST

BUSY

WAKEUP

CONVERT

Figure 12. Wake-Up Timing Diagram (Burst Clock)

Page 11

REV. A

AD7470/AD7472

–11–

OPERATING MODES

The AD7470 and AD7472 have two possible modes of operation depending on the state of the CONVST pulse at the end of a conversion, Mode 1 and Mode 2. There is a continuous clock on the CLK IN pin.

Mode 1 (High Speed Sampling)

In this mode of operation the CONVST pulse is brought high before the end of conversion i.e., before the BUSY goes low (see Figure 10). If the CONVST pin is brought from high to low while BUSY is high, the conversion is restarted. When operating in this mode a new conversion should not be initiated until 135 ns after BUSY goes low. This acquisition time allows the track/ hold circuit to accurately acquire the input signal. As mentioned earlier, a read should not be done during a conversion. This mode facilitates the fastest throughput times for the AD7470/ AD7472.

Mode 2 (Sleep Mode)

Figure 13 shows AD7470/AD7472 in Mode 2 operation where the ADC goes into sleep mode after conversion. The CONVST line is brought low to initiate a conversion and remains low until after the end of conversion. If CONVST goes high and low again while BUSY is high, the conversion is restarted. Once the BUSY line goes from a high to a low, the CONVST line has its status checked and, if low, the part enters sleep mode.

The device wakes up again on the rising edge of the CONVST signal. There is a wake-up time of typically 1 µs after the rising edge of CONVST before the BUSY line can go high to indicate start of conversion. BUSY will only go high once CONVST goes low. The CONVST line can go from a high to a low during this wake-up time, but the conversion will still not be initiated until after the 1 µs wake-up time. Superior power performance can be achieved in this mode of operation by waking up the AD7470 and AD7472 only to carry out a conversion.

Burst Mode

Burst mode on the AD7470/AD7472 is a subsection of Mode 1 and Mode 2, the clock is noncontinuous. Figure 12 shows how the ADC works in burst mode for Mode 2. The clock needs only to be switched on during conversion, minimum of 12 clock cycles for the AD7470 and 14 clock cycles for the AD7472. As the clock is off during nonconverting intervals, system power is saved. The BUSY signal can be used to gate the CLK IN pulses. The ADC does not begin the conversion process until the first

CONVST

BUSY

DBx

WAKEUP

CONVERT

Figure 13. Mode 2 Operation

CLK IN rising edge after BUSY goes high. The clock needs to start less than two clock cycles away from the CONVST active edge otherwise INL deteriorates; e.g., if the clock frequency is 28 MHz the clock must start within 71.4 ns of CONVST going low. In Figure 12 the A-D converter section is put into sleep mode once conversion is completed and on the rising edge of CONVST it is woken up again; the user must be wary of the wake-up time as this will reduce the sampling rate of the ADC.

DRIVE

The V

DRIVE

pin is used as the voltage supply to the output driv-

ers and is a separate supply from AV

and DVDD. The purpose of using a separate supply for the output drivers is that the user can vary the output high voltage, V

, from the VDD supply to

the AD7470/AD7472. For example, if AV

and DVDD is using

a 5 V supply, the V

DRIVE

pin can be powered from a 3 V supply. The ADC has better dynamic performance at 5 V than at 3 V, so operating the part at 5 V, while still being able to interface to 3 V parts, pushes the AD7470/AD7472 to the top bracket of high performance 10-bit/12-bit A/Ds. Of course, the ADC can have its V

DRIVE

and DVDD pins connected together and be pow-

ered from a 3 V or 5 V supply.

All outputs are powered from V

DRIVE

. These are all the data out

pins and the BUSY pin. The CONVST, CS, RD and CLK IN signals are related to the DV

voltage.

POWER-UP

It is recommended that the user performs a dummy conversion after power-up, as the first conversion result could be incorrect. This also ensures that the parts is in the correct mode of operation. The recommended power-up sequence is as follows:

1 > GND 4 > Digital Inputs 2 > V

5 > REF IN

3 > V

DRIVE

6 > V

Power vs. Throughput

The two modes of operation for the AD7470 and AD7472 will produce different power versus throughput performances, Mode 1 and Mode 2; see Operating Modes section of the data sheet for more detailed descriptions of these modes. Mode 2 is the Sleep Mode of the part and it achieves the optimum power performance.

Page 12

REV. A

AD7470/AD7472

–12–

Mode 1

Figure 14 shows the AD7472 conversion sequence in Mode 1 using a throughput rate of 500 kSPS and a clock frequency of 26 MHz. At 5 V supply the current consumption for the part when converting is 2 mA and the quiescent current is 650 µA. The conversion time of 531.66 ns contributes 2.658 mW to the overall power dissipation in the following way:

(531.66 ns/2 µs) × (5 × 2 mA) = 2.658 mW

The contribution to the total power dissipated by the remaining

1.468 µs of the cycle is 2.38 mW.

(1.468 µs/2 µs) × (5 × 650 µA) = 2.38 mW

Thus the power dissipated during each cycle is:

2.658 mW + 2.38 mW = 5.038 mW

CONVST

BUSY

531.66ns 1.468␮s

2␮s

CONVERT

QUIESCENT

Figure 14. Mode 1 Power Dissipation

Mode 2

Figure 15 shows the AD7472 conversion sequence in Mode 2 using a throughput rate of 500 kSPS and a clock frequency of 26 MHz. At 5 V supply the current consumption for the part when converting is 2 mA, while the sleep current is 1 µA max. The power dissipated during this power-down is negligible and is thus not worth considering in the total power figure. During the wake-up phase, the AD7472 will draw 650 µA. Overall power dissipated is:

531 66 2 5 2 1 2 5 650 4 283./ / .ns s mA s s A mWµµµµ

()

××

()

××

()

CONVST

BUSY

WAKEUP

531.66ns 1.468␮s

2␮s

1␮s

CONVERT

QUIESCENT

Figure 15. Mode 2 Power Dissipation

Figure 16 and Figure 17 show a typical graphical representation of Power vs. Throughput for the AD7472 when in (a) Mode 1 @ 5 V and 3 V and Mode 2 @ 5 V and 3 V.

THROUGHPUT – kHz

50 300

POWER – mW

1500130011001000800600

+5V

+3V

Figure 16. Power vs. Throughput (Mode 1 @ 5 V and 3 V)

THROUGHPUT – kHz

50 100

POWER – mW

750700650600300200

150 350250 400 450 500 550

+5V

+3V

Figure 17. Power vs. Throughput (Mode 2 @ 5 V and 3 V)

CODE

–1

INL ERROR – LSB

4096

–0.8

358430722560204815361024512

–0.6

–0.4

–0.2

0.2

0.4

0.6

0.8

Figure 18. Typical INL for 2.75 V @ +25°C

Page 13

REV. A

AD7470/AD7472

–13–

CODE

–1

DNL ERROR – LSB

4096

–0.8

358430722560204815361024512

–0.6

–0.4

–0.2

0.2

0.4

0.6

0.8

Figure 19. Typical DNL for 2.75 V @ +25°C

INPUT FREQUENCY – kHz

SNR + D – dB

2000

100050020010050

AD7472 +5V

AD7472 +3V

AD7470 +5V

AD7470 +3V

Figure 20. Typical SNR+D vs. Input Tone

INPUT FREQUENCY – kHz

THD – dB

2000

100050020010050

AD7472 +5V

AD7472 +3V

AD7470 +5V

AD7470 +3V

Figure 21. Typical THD vs. Input Tone

SUPPLY – Volts

69.2

2.5

SNR – dB

2.75 3 3.25 3.5 3.75 4 4.25 4.5 4.75 5 5.25

69.4

69.6

69.8

70.2

70.4

70.6

+85ⴗC

+25ⴗC

–40ⴗC

Figure 22. Typical SNR vs. Supply

FREQUENCY – Hz

–120

100000 200000 300000 400000 500000 600000

–100

–80

–60

–40

–20

Figure 23. Typical SNR @ 500 kHz Input Tone

FREQUENCY – kHz

–3.8

100 1000 10000 100000

–3.3

–2.8

–2.3

–1.8

–1.3

–0.8

0.2

–0.3

+5V

+3V

Figure 24. Typical Bandwidth

Page 14

REV. A

AD7470/AD7472

–14–

GROUNDING AND LAYOUT

The analog and digital power supplies are independent and separately pinned out to minimize coupling between analog and digital sections within the device. To complement the excellent noise performance of the AD7470/AD7472 it is imperative that care be given to the PCB layout. Figure 25 shows a recommended connection diagram for the AD7470/AD7472.

All of the AD7470/AD7472 ground pins should be soldered directly to a ground plane to minimize series inductance. The AV

, DV

and V

DRIVE

pins should be decoupled to both the analog and digital ground planes. The large value capacitors will decouple low frequency noise to analog ground, the small value capacitors will decouple high frequency noise to digital ground. All digital circuitry power pins should be decoupled to the digital ground plane. The use of ground planes can physically separate sensitive analog components from the noisy digital system. The two ground planes should be joined in only one place and should not overlap so as to minimize capacitive coupling between them. If the AD7470/AD7472 is in a system where multiple devices require AGND to DGND connections, the connection should still be made at one point only, a star ground point, which should be established as close as possible to the AD7470/AD7472.

Noise can be minimized by applying some simple rules to the PCB layout: analog signals should be kept away from digital signals; fast switching signals like clocks should be shielded with digital ground to avoid radiating noise to other sections of the board and clock signals should never be run near the analog inputs; avoid running digital lines under the device as these will couple noise onto the die; the power supply lines to the AD7470/ AD7472 should use as large a trace as possible to provide a low impedance path and reduce the effects of glitches on the power supply line; avoid crossover of digital and analog signals and place traces that are on opposite sides of the board at right angles to each other.

Noise to the analog power line can be further reduced by use of multiple decoupling capacitors as shown in Figure 25. Decoupling capacitors should be placed directly at the power inlet to the PCB and also as close as possible to the power pins of the AD7470/AD7472. The same decoupling method should be used on other ICs on the PCB, with the capacitor leads as short as possible to minimize lead inductance.

POWER SUPPLIES

Separate power supplies for AV

and DV

are desirable but if

necessary DV

may share its power connection to AVDD. The

digital supply (DV

) must not exceed the analog supply (AVDD)

by more than 0.3 V in normal operation.

MICROPROCESSOR INTERFACING AD7470/AD7472 to ADSP-2185 Interface

Figure 26 shows a typical interface between the AD7470/AD7472 and the ADSP-2185. The ADSP-2185 processor can be used in one of two memory modes, Full Memory Mode and Host Mode. The Mode C pin determines in which mode the processor works. The interface in Figure 26 is set up to have the processor working in Full Memory Mode, which allows full external addressing capabilities.

When the AD7470/AD7472 has finished converting, the BUSY line requests an interrupt through the IRQ2 pin. The IRQ2 interrupt has to be set up in the interrupt control register as edge-sensitive. The DMS (Data Memory Select) pin latches in the address of the A/D into the address decoder. The read operation is thus started.

ADDRESS

DECODER

AD7470/ AD7472*

ADSP-2185*

A0–A15

DMS

IRQ2

MODE C

D0–D23

CONVST

BUSY

DB0–DB9 (DB11)

ADDRESS BUS

DATA BUS

100k⍀

*ADDITIONAL PINS OMITTED FOR CLARITY

OPTIONAL

Figure 26. Interfacing to the ADSP-2185

AD7470/AD7472 to ADSP-21065 Interface

Figure 27 shows a typical interface between the AD7470/AD7472 and the ADSP-21065L SHARC

processor. This interface is an

example of one of three DMA handshake modes. The MSX

AD7470/

AD7472

AD780

10␮F

1nF

OUT

1nF

10␮F

0.1␮F

10␮F

AGND

DGND

DRIVE

VREF

0.1␮F47␮F

ANALOG SUPPLY +5V

0.1␮F

Figure 25. Decoupling Circuit

SHARC is a registered trademark of Analog Devices, Inc.

Page 15

REV. A

AD7470/AD7472

–15–

control line is actually three memory select lines. Internal ADDR

25–24

are decoded into MS

3-0

, these lines are then asserted

as chip selects. The DMAR

(DMA Request 1) is used in this setup as the interrupt to signal end of conversion. The rest of the interface is standard handshaking operation.

AD7470/

AD7472*

ADSP-21065L*

ADDR0–ADDR

D0–D31

CONVST

BUSY

DB0–DB9 (DB11)

ADDRESS BUS

DATA BUS

*ADDITIONAL PINS OMITTED FOR CLARITY

OPTIONAL

DMAR

ADDRESS

LATCH

ADDRESS BUS

ADDRESS DECODER

Figure 27. Interfacing to ADSP-21065L

AD7470/AD7472 to TMS320C25 Interface

Figure 28 shows an interface between the AD7470/AD7472 and the TMS320C25. The CONVST signal can be applied from the TMS320C25 or from an external source. The BUSY line interrupts the digital signal processor when conversion is completed. The TMS320C25 does not have a separate RD output to drive the AD7470/AD7472 RD input directly. This has to be generated from the processor STRB and R/W outputs with the addition of some glue logic. The RD signal is OR-gated with the MSC signal to provide the WAIT state required in the read cycle for correct interface timing. The following instruction is used to read the conversion from the AD7470/AD7472:

IN D,ADC

where D is Data Memory address and the ADC is the AD7470/ AD7472 address. The read operation must not be attempted during conversion.

ADDRESS DECODER

AD7470/ AD7472*

TMS320C25*

A0–A15

STRB

R/W

READY

DMD0–DMD15

CONVST

BUSY

DB0–DB9 (DB11)

ADDRESS BUS

*ADDITIONAL PINS OMITTED FOR CLARITY

OPTIONAL

MSC

DATA BUS

Figure 28. Interfacing to the TMS320C25

AD7470/AD7472 to PIC17C4x Interface

Figure 29 shows a typical parallel interface between the AD7470/ AD7472 and PIC17C42/43/44. The microcontroller sees the A/D as another memory device with its own specific memory address on the memory map. The CONVST signal can either be controlled by the microcontroller or an external source. The BUSY signal provides an interrupt request to the microcontroller when a conversion ends. The INT pin on the PIC17C42/43/44 must be configured to be active on the negative edge. PORTC and PORTD of the microcontroller are bidirectional and used to address the AD7470/AD7472 and also to read in the 10-bit (AD7470) or 12-bit (AD7472) data. The OE pin on the PIC can be used to enable the output buffers on the AD7470/AD7472 and preform a read operation.

*ADDITIONAL PINS OMITTED FOR CLARITY

ADDRESS DECODER

ADDRESS

LATCH

OPTIONAL

PIC17C4x*

AD0–AD15

INT

AD7470/ AD7472*

CONVST

BUSY

DB0–DB9 (DB11)

ALE

Figure 29. Interfacing to the PIC17C4x

AD7470/AD7472 to 80C186 Interface

Figure 30 shows the AD7470/AD7472 interfaced to the 80C186 microprocessor. The 80C186 DMA controller provides two independent high speed DMA channels where data transfer can occur between memory and I/O spaces. (The AD7470/AD7472 occupies one of these I/O spaces.) Each data transfer consumes two bus cycles, one cycle to fetch data and the other to store data.

After the AD7470/AD7472 has finished conversion, the BUSY line generates a DMA request to Channel 1 (DRQ1). As a result of the interrupt, the processor performs a DMA READ operation which also resets the interrupt latch. Sufficient priority must be assigned to the DMA channel to ensure that the DMA request will be serviced before the completion of the next conversion. This configuration can be used with 6 MHz and 8 MHz 80C186 processors.

80C186*

AD0–AD15

A16–A19

DRQ1

ADDRESS/DATA BUS

DATA BUS

*ADDITIONAL PINS OMITTED FOR CLARITY

ADDRESS

LATCH

ADDRESS BUS

ADDRESS

DECODER

ALE

RSQ

AD7470/

AD7472*

CONVST

BUSY

DB0–DB9 (DB11)

OPTIONAL

Figure 30. Interfacing to the 80C186

Page 16

REV. A

AD7470/AD7472

–16–

OUTLINE DIMENSIONS

Dimensions shown in inches and (mm).

C3600–0–3/00 (rev. A)

PRINTED IN U.S.A.

24-Lead SOIC

(R-24)

0.0125 (0.32)

0.0091 (0.23)

8ⴗ 0ⴗ

0.0291 (0.74)

0.0098 (0.25)

ⴛ 45ⴗ

0.0500 (1.27)

0.0157 (0.40)

SEATING PLANE

0.0118 (0.30)

0.0040 (0.10)

0.0192 (0.49)

0.0138 (0.35)

0.1043 (2.65)

0.0926 (2.35)

0.0500 (1.27)

BSC

24 13

0.4193 (10.65)

0.3937 (10.00)

0.2992 (7.60)

0.2914 (7.40)

PIN 1

0.6141 (15.60)

0.5985 (15.20)

24-Lead TSSOP

(RU-24)

24 13

121

0.256 (6.50)

0.246 (6.25)

0.177 (4.50)

0.169 (4.30)

PIN 1

0.311 (7.90)

0.303 (7.70)

SEATING

PLANE

0.006 (0.15)

0.002 (0.05)

0.0118 (0.30)

0.0075 (0.19)

0.0256 (0.65) BSC

0.0433 (1.10) MAX

0.0079 (0.20)

0.0035 (0.090)

0.028 (0.70)

0.020 (0.50)

8ⴗ 0ⴗ