MAX7421EUA+

Overview

The MAX7421EUA+ is a fifth-order, low-pass switched-capacitor filter (SCF) from the MAX7418–MAX7425 family. It features an elliptic response with a transition ratio of 1.25 and operates from a single +5V supply. The device draws 3mA in operating mode and 0.2μA in shutdown mode. Corner frequencies are adjustable from 1Hz to 45kHz via a 100:1 clock-to-corner frequency ratio using either an internal oscillator or external clock. Key electrical parameters include a typical output offset voltage of ±4mV, a power-supply rejection ratio (PSRR) of 70dB, and a maximum capacitive load drive of 500pF. It is housed in an 8-pin μMAX package.

Feature Summary

• Elliptic low-pass filter response with a sharp rolloff characteristic defined by a 1.25 transition ratio.
• Clock-tunable corner frequency ranging from 1Hz to 45kHz, supporting both self-clocking and external clocking modes.
• Low-power operation with a dedicated shutdown mode that reduces supply current to 0.2μA.
• Single-supply operation optimized for +5V systems with low output offset voltage.

Applications

• ADC anti-aliasing
• DAC post-filtering
• CT2 base stations
• Speech processing

Procurement Notes

Verify the component authenticity by checking the manufacturer marking against the official datasheet specifications. Confirm the suffix 'EUA' corresponds to the -40°C to +85°C temperature range and the 8-pin μMAX package. Ensure the ordering information matches the specific elliptic response variant required for the design.

Selection Notes

Select the MAX7421EUA+ when an elliptic filter response with a steep 1.25 transition ratio is required for +5V applications. This part is suitable for designs needing precise stopband attenuation compared to Butterworth or Bessel variants. Consider the 100:1 clock-to-corner ratio when designing the clock generation circuitry to achieve the desired cutoff frequency.

Part Context

The MAX7421EUA+ belongs to the MAX7418–MAX7425 series of fifth-order, low-pass switched-capacitor filters. These devices utilize a passive network emulation approach using switched-capacitor integrators, offering lower component sensitivity than traditional biquadratic designs. The series covers elliptic, Bessel, and Butterworth responses across +5V and +3V supply options.

Replacement Considerations

The MAX7418EUA+, MAX7422EUA+, and MAX7425EUA+ are direct members of the same family with identical pinouts and packaging. They differ primarily in filter response characteristics and transition ratios. Verify that the alternative response type meets the system's frequency domain requirements before substitution.

FAQ

How is the corner frequency determined for the MAX7421?

The corner frequency is set by the clock frequency divided by 100. It can be generated internally using an external capacitor on the CLK pin or provided externally.

What is the purpose of the OS pin?

The Offset Adjust (OS) pin allows for adjustment of the DC output level. It can be connected to the COM pin if no offset adjustment is needed, or driven by an external bias voltage.

Can the MAX7421 operate with dual supplies?

Yes, while designed for single-supply operation, it can be used with dual supplies by connecting COM to system ground and GND to the negative supply.