The AD7822/AD7825/AD7829 are high speed, 1-, 4-, and 8-channel, microprocessor-compatible, 8-bit analog-to-digital converters with a maximum throughput of 2 MSPS. The AD7822/ AD7825/AD7829 contain an on-chip reference of 2.5 V (2% tolerance); a track-and-hold amplifier; a 420 ns, 8-bit half-flash ADC; and a high speed parallel interface. The converters can operate from a single 3 V ± 10% and 5 V ± 10% supply.
The AD7822/AD7825/AD7829 combine the convert start and power-down functions at one pin, that is, the CONVST pin. This allows a unique automatic power-down at the end of a conversion to be implemented. The logic level on the CONVST pin is sampled after the end of a conversion when an EOC (end of conversion) signal goes high. If it is logic low at that point, the ADC is powered down. The AD7822 and AD7825 also have a separate power-down pin (see the Operating Modes section).
The parallel interface is designed to allow easy interfacing to microprocessors and DSPs. Using only address decoding logic, the parts are easily mapped into the microprocessor address space. The EOC pulse allows the ADCs to be used in a stand-alone manner (see the Parallel Interface section.)
The AD7822 and AD7825 are available in 20-lead and 24-lead, 0.3" wide, plastic dual in-line packages (PDIP); 20-lead and 24-lead standard small outline packages (SOIC); and 20-lead and 24-lead thin shrink small outline packages (TSSOP). The AD7829 is available in a 28-lead, 0.6" wide PDIP; a 28-lead SOIC; and a 28-lead TSSOP.
**Product Highlights**
1. Fast Conversion Time. The AD7822/AD7825/AD7829 have a conversion time of 420 ns. Faster conversion times maximize the DSP processing time in a real-time system.
2. Analog Input Span Adjustment. The VMID pin allows the user to offset the input span. This feature can reduce the requirements of single-supply op amps and take into account any system offsets.
3. FPBW (Full Power Bandwidth) of Track-and-Hold. The track-and-hold amplifier has an excellent high frequency performance. The AD7822/AD7825/AD7829 are capable of converting full-scale input signals up to a frequency of 10 MHz. This makes the parts ideally suited to subsampling applications.
4. Channel Selection. Channel selection is made without the necessity of writing to the part.
**Applications**
Data acquisition systems, DSP front ends
Disk drives
Mobile communication systems, subsampling applications
### Features and Benefits
8-bit half-flash ADC with 420 ns conversion time
1, 4 and 8 Single-Ended Analog Input Channels Available with Input Offset Adjust
On-Chip Track-and-Hold
SNR Performance Given for Input Frequencies Up to 10 MHz
Automatic Power-Down at the End of Conversion
On-Chip Reference (2.5 V)
Wide Operating Supply Range
3 V ± 10% and 5 V ± 10%
Input Ranges:
0 V to 2 V p-p, VDD = 3 V ± 10%
0 V to 2.5 V p-p, VDD = 5 V ± 10%
Flexible Parallel Interface with EOC Pulse to Allow Stand-Alone Operation
