9.1 Application Information

Figure 50 shows the basic DAC1282 connection. Bipolar analog supplies are shown (±2.5 V). Single-supply operation is also possible with AVDD = 5 V and AVSS = GND. The digital supply range is 1.65 V to 3.6 V.

A low-noise, low-drift reference is recommended for best performance, such as the REF5050 (+5 V) and REF5045 (+4.5 V). Best signal-to-noise ratio is achieved with a 5-V reference, although a 4.5-V reference (REF5045) can be used with 1-dB loss in SNR. The 4.5-V reference can be operated from a 5-V supply. AVSS (pin 14) is the key reference ground point and should be connected to the reference ground terminal using a star connection. C₁ and C₂ are the required 1-nF output filter capacitors. The capacitors should be of the low volt-coefficient type (such as a COG ceramic or similar) and placed close to the device pins. Output resistors, R₁ and R₂, decouple the DAC to ensure best performnace when driving capacitive loads. The output is shown routed to the signal switch, providing a second, switched DAC output.

Figure 50. Basic Connection

9.2 Typical Applications

9.2.1 Single-Channel Seismic System

Figure 51 illustrates a single-channel data acquisition concept for seismic. The DAC1282 is used to test both the ADC and geophone. The DAC1282 connects directly to channel 1 of the ADC. Tests of the ADC include THD, pulse, input noise, common-mode, etc. The DAC output and ADC sample timing are controlled by the SYNC input pins.

The geophone connects to channel 2 of the ADC through input protection and optional filter networks. The DAC connects to the geophone using the integrated signal switch. Series resistors isolate the geophone from the DAC output. Geophone test capabilities include impulse, THD, leakage, and common-mode.

Figure 51. Single-Channel Seismic System

9.2.2 Four-Channel Seismic System

Figure 52 illustrates a four-channel system. The switched DAC1282 output is routed to the ADC inputs. The signal from the DAC switch is used to perform sensor impulse testing by opening the switch while digitizing the response.

Figure 52. Four-Channel Seismic System