Microchip Technology CD821A

Overview

CD821A from Microsemi is a monolithic temperature-compensated zener reference diode die, designed as a precision voltage reference in high-reliability analog and power-supply feedback circuits. It delivers 5.9–6.5 V zener voltage at 7.5 mA test current, with 13 Ω zener impedance, ±0.01 %/°C temperature coefficient, and operates across –65°C to +175°C.

For engineers reviewing the CD821A datasheet, CD821A pinout, CD821A application, or CD821A equivalent, key selection considerations include its low-TC stability over military temperature range, silicon-dioxide junction protection, compatibility with wire bonding and conductive die attach, and qualification per MIL-PRF-19500/159 JANHC/JANKC levels.

Technical Context

The CD821A is a bare-die zener reference optimized for high-stability voltage regulation in space-constrained, high-temperature environments. Its monolithic construction integrates temperature compensation circuitry directly into the silicon, eliminating external components while maintaining tight voltage tolerance and low dynamic impedance.

Zener operation requires cathode bias positive relative to anode; the device features three metallized terminals - cathode (Al), anode (Al), and non-functional test pad (Al) - with gold backside metallization for thermal and electrical isolation. Backside must remain electrically isolated for specified performance.

Key Specifications

Pinout & Package

CD821A is supplied as a bare semiconductor die in JANHC/JANKC qualified outline: 0.030" × 0.009" (0.76 mm × 0.23 mm) with 0.010" ±0.002" thickness. Backside is gold-metallized for thermal dissipation and electrical isolation.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar zener reference applications.

Compared with CD823A and CD827A, the CD821A provides the highest cost-efficiency for applications requiring robust 96 mV max drift and ±0.01 %/°C stability - making it ideal for industrial-grade power management where extreme precision is unnecessary but military-grade reliability is mandatory.

Availability

CD821A is available at Aetrix Electronics and suitable for high-reliability power supply references, aerospace voltage monitoring, downhole sensor conditioning, and military analog front-end designs requiring stable component supply across extended temperature ranges and long product lifecycles.

Supply support for CD821A 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

Microsemi (now part of Microchip Technology) is a U.S.-based semiconductor company specializing in high-reliability analog, RF, and radiation-hardened components for aerospace, defense, and industrial markets.

The CD821A belongs to Microsemi's MIL-qualified monolithic zener reference die family, engineered specifically for precision voltage referencing in extreme-temperature, high-integrity systems where hermetic packaging and long-term parametric stability are critical.

FAQ

What is the zener voltage tolerance of CD821A?

The CD821A has a zener voltage range of 5.9 V to 6.5 V at 7.5 mA test current (I_ZT). This 600 mV span reflects the initial calibration tolerance under standard test conditions; actual unit-level V_Z is measured and binned during qualification. The CD821A does not specify a tighter tolerance band - design margins must accommodate this full range in feedback networks.

Is CD821A compatible with solder reflow assembly?

No, CD821A is explicitly incompatible with solder reflow per its datasheet. The device uses aluminum top metallization and gold backside, which cannot withstand typical Pb-free reflow thermal profiles. It is qualified only for wire bonding and conductive die attach (e.g., silver epoxy). Using solder reflow risks metallurgical degradation and parametric failure of the CD821A.

How does CD821A achieve temperature compensation?

The CD821A achieves temperature compensation through monolithic integration of complementary zener and forward-biased junctions on a single silicon die. This architecture cancels inherent negative TC of the zener with positive TC of the forward diode, yielding net ±0.01 %/°C stability. No external components or trimming resistors are required - compensation is built into the CD821A's semiconductor structure.

What is the purpose of the third terminal (test pad) on CD821A?

The third terminal on CD821A is a dedicated test pad made of aluminum, intended solely for wire bond process development and evaluation. It has no electrical connection to the active zener junction and must not be bonded or contacted in production assemblies. Its presence does not affect CD821A functionality - the device operates strictly as a two-terminal zener between cathode and anode.

Can CD821A replace 1N821 in existing designs?

Yes, CD821A is electrically equivalent to 1N821 per datasheet statement and shares identical zener voltage range, test current, impedance, and temperature behavior. However, CD821A is a bare die while 1N821 is a through-hole DO-35 package - mechanical integration, thermal management, and assembly method differ significantly. System redesign is required to accommodate CD821A's die format, though electrical substitution is validated.