AD7112CN

Overview

The AD7112CN is a dual logarithmic digital-to-analog converter (LOGDAC) manufactured by Analog Devices Inc. It features two independent multiplying DACs capable of attenuating analog input signals over a dynamic range of 0 dB to 72 dB with a resolution of 0.375 dB per step. The device operates on a single +5 V supply and utilizes an internal 17-bit R-2R ladder structure driven by 8-bit binary inputs. Key electrical specifications include a maximum gain error of ±0.15 dB, output leakage current of 400 nA max at extended temperatures, and AC feedthrough of -90 dB. The component is housed in a 20-pin Plastic DIP package and supports an operating temperature range from –40 °C to +85 °C.

Feature Summary

• Dual Multiplying DAC Architecture: Two independent channels provide simultaneous signal attenuation with 0.375 dB resolution.
• Wide Dynamic Range: C Grade version guarantees monotonic operation up to 72 dB attenuation.
• High Accuracy: Gain error is specified at ±0.15 dB max, ensuring precise logarithmic control.
• Flexible Interface: Compatible with standard microprocessors via CS, WR, and 8-bit data lines.

Applications

• Automatic Gain Control (AGC) Systems
• Programmable State Variable Filters
• Audio Attenuators

Procurement Notes

Verify the ordering suffix 'CN' corresponds to the Plastic DIP (N-20) package and the C Grade accuracy specification (0 dB to 72 dB range). Confirm that the lead time and availability status are current, as this is a legacy component. Ensure compliance with RoHS directives if required, noting the datasheet indicates the part may be leaded.

Selection Notes

Select the AD7112CN when a dual-channel logarithmic attenuation solution is required within the –40 °C to +85 °C industrial temperature range. Choose this specific grade if the application demands guaranteed monotonicity up to 72 dB; for full 88.5 dB monotonicity, the B Grade variant is necessary. Ensure the external output amplifier has low bias current (<10 nA) and low offset voltage (<50 µV) to maintain DC accuracy.

Part Context

The AD7112 belongs to the LOGDAC family of multiplying D/A converters from Analog Devices. It serves as a monolithic solution for applications requiring precise, digitally controlled signal attenuation. The CN suffix denotes the commercial temperature range and plastic DIP packaging, distinguishing it from the hermetic or surface-mount variants like the BR or BN models.

Replacement Considerations

Public confirmed substitute part numbers are not available in the provided documentation. Designers should verify pin compatibility and transfer function linearity if considering alternative dual LOGDACs.

FAQ

What is the maximum attenuation range for the AD7112CN?

The AD7112CN (C Grade) guarantees monotonic operation up to 72 dB of attenuation. The absolute maximum range is 88.5 dB, but monotonicity is not guaranteed beyond 72 dB for this specific grade.

How does the AD7112 handle digital-to-analog glitch impulse?

The typical digital-to-analog glitch impulse is 10 nV·s, measured during input code transitions such as 10000000 to 00000000.

What is the recommended feedback resistance configuration?

The device includes internal feedback resistors with values between 9.3 kΩ and 15.7 kΩ. External trim resistors can be used to adjust the gain error at 0 dB attenuation.