Analog Devices Inc. 123115-HMC681ALP5

Overview

HMC681ALP5E from Hittite Microwave Corporation (now part of Analog Devices) is a GaAs MMIC 6-bit digital variable gain amplifier with serial SPI interface, operating from DC to 1 GHz. It delivers programmable gain from +13.5 dB to +45 dB in 0.5 dB steps, features +36 dBm output IP3 and 2.8 dB noise figure at maximum gain, and is used in RF/IF signal chains for cellular infrastructure and microwave radio.

For engineers reviewing the HMC681ALP5E datasheet, HMC681ALP5E pinout, HMC681ALP5E application, or HMC681ALP5E equivalent, key selection criteria include its 0.5 dB LSB resolution, ±0.25 dB typical gain step error, single +5 V supply operation, 32-lead 5×5 mm QFN RoHS-compliant package, and serial control timing compliance (tSCK ≥ 100 ns, tLEW ≥ 10 ns).

Technical Context

The HMC681ALP5E implements a digitally controlled attenuator-amplifier architecture using GaAs MMIC process, supporting DC-coupled RF paths with external AC-ground capacitors (ACG1–ACG7) enabling near-DC operation. Its 6-bit serial interface (SERIN/CLK/LE) loads gain settings MSB-first with latch-edge synchronization and supports power-up state selection via PUP1/PUP2 pins.

It operates across two frequency bands-50–350 MHz and 350–1000 MHz-with matching network components optimized per band. Gain accuracy is referenced to maximum gain state, with total error bounded by ±(0.15 + 3% of relative gain setting), and input/output return loss exceeds 20 dB across full bandwidth.

Key Specifications

Pinout & Package

Package: RoHS-compliant 5×5 mm leadless QFN with exposed thermal paddle; MSL1 rating; 100% matte tin lead finish; requires soldering all ground leads and paddle to PCB RF ground.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar digital VGA applications.

Compared with HMC681ALP5E, HMC626ALP5E eliminates serial interface overhead but increases PCB routing complexity, while ADL5330ACPZ-R7 extends usable bandwidth beyond 1 GHz at the cost of reduced linearity and higher noise-making HMC681ALP5E optimal for sub-1 GHz infrastructure with strict distortion and noise requirements.

Availability

HMC681ALP5E is available at Aetrix Electronics and suitable for cellular infrastructure, microwave radio backhaul, and test equipment requiring stable component supply, long-lifecycle support, and traceable GaAs MMIC sourcing.

Supply support for HMC681ALP5E includes scheduled delivery planning, volume procurement assistance, BOM continuity management, traceable sourcing, and lifecycle availability coordination for OEM customers, industrial embedded developers, connected-device designers, and electronics production programs.

Manufacturer

Hittite Microwave Corporation, acquired by Analog Devices in 2014, specialized in high-performance RFICs and MMICs for defense, wireless infrastructure, and instrumentation markets.

The HMC681ALP5E belongs to Hittite's digital VGA product line designed specifically for high-linearity, low-noise gain control in DC–1 GHz receiver and transmitter signal chains of 3G/4G/WiMAX systems.

FAQ

What is the absolute maximum RF input power rating for the HMC681ALP5E?

The HMC681ALP5E has an absolute maximum RF input power rating of –10.5 dBm at +85 °C when operating at maximum gain. This rating increases by 0.5 dB for every 0.5 dB reduction in gain setting, reaching up to +10 dBm at minimum gain (insertion loss state). Exceeding these limits risks permanent damage to the GaAs MMIC core.

Does the HMC681ALP5E require external DC blocking capacitors, and where are they needed?

Yes, the HMC681ALP5E requires external DC blocking capacitors on RFin1/RFin2 (pins 2, 20), RFout1/RFout2 (pins 4, 22), and ATTin/ATTout (pins 6, 19). These are mandatory because all RF ports are DC-coupled. Capacitor values depend on lowest operating frequency: e.g., 3300 pF for 50–350 MHz, 100 pF for 350–1000 MHz bands.

How does the power-up state functionality work on the HMC681ALP5E?

The HMC681ALP5E uses PUP1 and PUP2 pins (25, 26) to define its initial gain state after power-on. When LE is held low during startup, the logic levels on PUP1/PUP2 select one of four preset states per the PUP truth table (e.g., 00 = –31.5 dB, 11 = insertion loss). The selected state latches ~200 ms after Vdd stabilization.

Can the HMC681ALP5E operate from a 3 V supply, and what are the implications?

No, the HMC681ALP5E is specified only for +5 V operation (Vdd = +5 V, absolute max 5.5 V). While digital input thresholds support 3 V logic levels (high = 2–5 V), the internal GaAs amplifier stages require +5 V for proper biasing and performance. Operating below +5 V degrades gain, IP3, and noise figure, and is outside qualified specifications.

What is the purpose of the ACG1–ACG7 pins on the HMC681ALP5E?

The ACG1–ACG7 pins (8–13, 15, 17) provide external AC-ground connection points for internal bias networks, enabling stable DC-coupled operation down to near-DC frequencies. Each requires a dedicated capacitor to RF ground; value selection (e.g., 330 pF or 100 pF) depends on the target low-frequency cutoff and must be placed as close as possible to the pin to minimize inductance.