Analog Devices, the market share leader in high performance converters and amplifiers, has introduced the AD7680, a 16-bit successive approximation register (SAR) ADC with 15-bits no missing codes in a 6-lead SOT 23 package. This is the industry's first 16-bit SAR ADC in this tiny package. Featuring a fast throughput rate of 100 kSPS, and using an advanced design technique to achieve low power dissipation 3 mW at 3 V and 15 mW at 5 V, typical this converter is the most recent addition to ADI's PulSAR family of 16-bit SAR ADCs. Because the AD7680 is based on the SAR architecture, there are no pipeline delays. The AD7680 was designed for a wide variety of portable and battery-powered applications in medical instrumentation, control systems, remote data acquisition, and mobile communications.

The ADC operates from a single 3.0 V to 5.25 V power supply and contains a low noise, wide bandwidth track/hold amplifier that guarantees performance with inputs up to 10 kHz. Data acquisition and conversion are controlled using the Chip Select pin and an external serial clock, allowing the device to interface with microprocessors or DSPs. The part goes into a low-power mode when the conversion is complete, reducing the average power dissipation and providing maximized efficiency at lower throughput rates. Power consumption in the shut-down mode is only 0.5 microamps maximum. The reference for the AD7680 is derived from the power supply, allowing the widest dynamic input range to the ADC.

Analog Devices, Inc., 804 Woburn Street, Wilmington, MA 01887. Tel: 1/800-ANALOGD (262-5643); Fax: 781-937-1021; http://www.analog.com

The highlights with this product are the size, power, and price. It's a 16-bit 100kSPS converter in a SOT 23-6 package. Yes, TI/Burr-Brown and Linear Technologies both offer a similar product. However, Analog Devices thinks there is room for another very small package. The SOT 23-6 package is only 3mm x 3mm versus the MSOP 8 with 15mm2 (3mm x 5mm). So it saves a little board space.

ADI thinks that saving power is another good reason to bring this product to market. The competitors' products dissipate more power than the ADI converter, just below 4.5mW for one and a little over 2mW for the other. ADI says their converter is expected to dissipate about 1.5mW.

The company is also touting this as a 16-bit no missing code part, but during the sampling stage they are being conservative and offering it as a 15-bit no missing code device. So what's the difference between 15-bit and 16-bit no missing code, and what does it mean to you? For 16-bit you have 65,536 codes (216 power). On a perfect 16-bit ADC you should see every least significant bit (LSB) transition from the analog input resulting in output code. When you guarantee 15-bit no missing code you will always see the second LSB, not the first LSB, so the second LSB transition will always be seen. This is to verify that you test the edge transition between adjacent codes. For the 7680 ADI tests all the codes and measures the differential non-linearity, which is the adjacent error between codes. Typically what happens, the codes will get so short that they will disappear, and that's when you have the missing code, and it will skip code and the analog input is increased. So what is meant by 15-bit no missing code is that the second LSB code will always be there but a high guarantee that LSB will also be there.

Power dissipation is very critical when you play in the battery-supplied, portable market. The parts operations are specified 3V and 5V. The part also has a power-down mode so that if you bring the chip-select pin high, which is used to initiate conversions, at the end of the conversion the power will go into a power-down and only draw 0.5 micro amps of current. The 85 dB SINAD at 10kHz is a nice feature compared to competition, because ADI guarantees AC specification for SINAD for THD for spurious-free dynamic range, so far the competition won't guarantee it. Why don't other manufacturers guarantee the 85 dB SINAD? This is probably because it would add to the price of the part since the only way to guarantee AC performance from +40 to -85 dB is if you do a true temperature test.

The VDD pin actually provides the reference for this part. Customers will need to regulate the line. ADI says that in subsequent data sheets they will show 100 nF and 1microF capacitors hanging off that supply line for decoupling purposes. That's how the part is tested by ADI.

ADI is featuring the SOT23-6 packaging for this part but they will also release it in the 8-lead MSOP. The 8-lead MSOP has already been qualified. One thousand parts are $6, the 16-bit no missing code is $7.94. The part is also compatible with all serial interfaces.

The AD7680 operates within the -40 to +85 degree C temperature range and is sampling now. It is priced at $6.00 in 1,000-piece quantities.

For more information: http://www.analog.com/PulSAR.