AD73322/AD73322L compatibility

Q Can I use the AD73322L as a replacement for the AD73322 and is it pin and software compatible? A The AD73322L is a cost reduced version of the AD73322 and is fabricated on a 0.35um process. In 3V applications, the AD73322L is pin for pin compatible with the AD73322 and like the AD73322 it has selectable sampling rates, which allow the user the option of trading-off low Group Delay for low sample Rate. (10/2012: Note that only the 44ld LQFP package models of AD73322 (and AD73322L) and the non-RoHS 28 ld SOIC-wide package models of AD73322 have been obsoleted. The AD73322 RoHS compliant 28 ld SOIC-wide packages are still in production).

AD73322: CD measurability

Q I want to make measurements at the tachometer output from dc-motors. This signal is a dc-voltage with ac-parts (if the motor accelerate or stop). The bandwith is therefore dc-max 2kHz. Can I use the ad-inputs of the ad73322 for such a measurement (in the datasheet are examples of dc-in and dc-out configurations) ? I ask, because I had the infoemation, thjat sigma-delta converters are not able to convert dc-signals. Do you have an layout example for the ad73322 in the RU28 (tssop) package? Do you also have some hints for decoupling if the supply voltage comes from an DC-DC converter (operates at 300kHz) ? A 1)Firstly I must explain that the AD73322…family of parts are designed for the telephony market, they are not characterised for DC operation, as you can see from the datasheet, we do not give typical DC specs of linearity, offset and gain errors. In addition , the analog front end is designed to work with a dc bias at Vref, therefore you may dc couple the i/p’s if the DC voltage of the signal is at the same dc voltage of the reference, otherwise you need to ac couple the signal. Sigma delta converters that are designed for the industrial market are very capable of converting dc signals, it is the ADC’s and DAC’s designed for the audio market that are not specified for DC operation, such as the AD73322. This allows us to produce CODEC’s that are very cost effective due to the elliminatin of the majority of DC testing that is carried out on our industrial converters. This address points to all the ap-notes available on sigma delta converter s that we have posted on our web site. We have a large range of converters that operate from DC to 2Khz, can you detail your i/p signal range, the supply available, the resolution required, the digital interface…plus any other relevant criteria, and I will get back to you as soon as possible with a possible solution/solutions. 2)I take it you are refering to a land pattern for the AD73322 TSSOP package. LANDS For pattern of the solder lands for any of our packages we recommend the standard layout. You should be able to find it at the website of the IPC (Institute for Interconnecting and Packaging Electronic Circuits). At http://www.ipc.org/ Under "Design" one will find a land pattern calculator that will enable one to view the patterns in the current standard as well as calculate new patterns from component data. It contains a user searchable database of patterns for components not yet approved by EIA or EIAJ. Analog Devices does not usually issue recommendations on land patterns because these are partially dependent on the board design rules used, and on the soldering processes used by the board assemblers. 3) Low dropout regulators are often used following switching regulators for better regulation and lower noise. Low dropout regulators such as the ADP3310 are desirable in these applications because they require only a small input to output series voltageto maintain regulation.

AD73322: Vref transfer function

Q Are the Vref directly connected to internal non inverting input of the op, or this is an principle schematic and the output op signal are only biased with Vref. In other word is the transfer function of the input stage : a)Vout= -Vin + 2Vref OR ? b)Vout= -Vin +Vref. Have you more details about input encoder and output decoder stages about the Vref biasing? A The input op amps on the AD73322 are accurately described by the diagram e.g. figure 30. If you were to dc-couple the inputs to the AD73322 you would theoretically get Vout = -Vin + Vin*(1+Rf/Rin) Therefore, if the bias level of the input signal is not Vref, but some other level, then the signal should be ac-coupled prior to the input resistor. Otherwise, the internal bias of the signal chain will be upset and clipping etc will happen. The inverting input of the op amp is capable of self-biasing itself at Vref, so you don't need to set the bias voltage to Vref externally, after the AC coupling capacitor. The output stage provides outputs that are biased around Vref.

AD73322L: Frequency response

Q I have a question relating to the operation of the AD73322L frequency response. I am testing the device with Sine wave tones ranging across the voice band between 300Hz and 3400Hz and Am finding that with a sampling rate of 16Khz, I am getting a 25% reduction in output at 3400 compared To 300Hz. Is this attenuation the correct operation of the device? I was expecting a flat response. Are there any setings in the registers which affect the frequency response? I found that 8Khz sampling gave distortion to the wave at 3400Hz so increased to 16Khz. A This is actually the correct or expected frequency response of the device. It uses a Sinc^3 filter to provide low group delay - however this filter response is quite "soft" with roll-off in the pass band that continues into the transition band. If the device is being used with a DSP as is normally the case, a Sinc^3 compensation filter operating at 16 kHz with decimation to 8 kHz can provide a flat response out to 3400 Hz and provides a sharp transition band. The other alternative is the AD74111 which is a mono codec but has a more traditional filter which gives flat pass band response and sharp transition band.

AD73322: FAQ - Documents - Audio

Products Mentioned

AD73322L Not Recommended for New Designs
The AD73322 and AD73322L are dual, front-end processor for general-purpose applications including speech and telephony. They feature two 16-bit A/D conversion...
Datasheet
AD73322L on Analog.com

AD73322: FAQ