SN74HC21DR - Dual 4-Input AND Gate SOIC-14 | Texas Instruments
부품 번호: SN74HC21DR ✓ 활성| 수량 | 단가 | 합계 |
|---|---|---|
| 1 | $0.35 | $0.35 |
| 10 | $0.31 | $3.10 |
| 100 | $0.22 | $22.00 |
| 500 | $0.18 | $90.00 |
| 1,000 | $0.14 | $140.00 |
SN74HC21DR 개요
A logic AND gate is a fundamental digital building block whose output asserts HIGH only when all of its inputs are HIGH. The SN74HC21 integrates two such gates on one silicon die, making it part of the broader logic IC hierarchy: gate -> combinational logic -> small-scale integration (SSI) -> 74HC CMOS family -> digital logic IC. Its function directly replaces the older LS/TTL 74LS21 in 5 V systems while adding CMOS advantages.
Key features include a wide 2 V to 6 V operating range covering 3.3 V, 5 V, and legacy 6 V rails; outputs that can drive up to 10 LSTTL loads; typical propagation delay of 11 ns at 5 V; plus/minus4 mA output drive at 5 V; and very low power consumption with a maximum ICC of only 20 uA. Maximum input current is just 1 uA, easing fan-out and pull-up resistor design.
Technically, the HC family uses CMOS technology with inputs that include clamp diodes, permitting interface to voltages slightly above VCC through current-limiting resistors. The balanced push-pull output stage delivers symmetric rise/fall times and rail-to-rail output swing, unlike bipolar TTL which loses headroom.
Typical applications include enable-signal gating in industrial controllers, safety interlock logic where multiple conditions must all be true, address decoding, and general glue logic in 3.3 V and 5 V embedded systems.
Design-wise, keep unused inputs tied to VCC or GND; never leave 4-input AND inputs floating, or noise can propagate to the output. Decouple VCC with 100 nF ceramic close to pin 14.
This page synthesizes distributor pricing, verified drop-in alternatives, pinout data, and practical design notes not found in the manufacturer datasheet alone.
드롭인 대체품: SN74HC21DR — 동일 패키지, 핀 호환. PCB 재작업이 필요한 다른 패키지 부품은 제외됩니다.
이 시리즈의 변형
다음과 드롭인 호환되는 동일 시리즈 모델: SN74HC21DR (동일 폼 팩터 및 풋프린트) — 차이점: Logic Family, Package.
빠른 비교 도구 — 나란히 비교할 대체 부품을 선택하십시오:
SN74HC21QDRQ1
✅ 드롭인📋 참조 대체품 (카탈로그에 없음)
CD74HC21M96
✅ 드롭인📋 참조 대체품 (카탈로그에 없음)
M74HC21RM13TR
✅ 드롭인📋 참조 대체품 (카탈로그에 없음)
HD74HC21RP-EL
✅ 드롭인📋 참조 대체품 (카탈로그에 없음)
74HC21D
✅ 드롭인📋 참조 대체품 (카탈로그에 없음)
SN74HC21DR 최대 정격 & 전기적 특성
| Logic Function | Dual 4-Input Positive-AND Gate |
| Logic Family | 74HC (High-Speed CMOS) |
| Supply Voltage Range | 2 V to 6 V |
| Output Drive Strength | 5.2 mA |
| Output Drive at 5 V | ±4 mA |
| LSTTL Load Drive | Up to 10 LSTTL loads |
| Typical Propagation Delay | 11 ns at 5 V |
| Maximum ICC | 20 uA |
| Maximum Input Current | 1 uA |
| 동작 온도 | -40C to +85C |
| 패키지 | SOIC (D), 14 pins |
| Number of Channels | 2 |
| Inputs per Gate | 4 |
| 실장 유형 | Surface Mount |
| Technology | CMOS with input clamp diodes |
| RoHS 상태 | Compliant |
SN74HC21DR 핀 구성
| 핀 1 | 1A — Gate 1 input A |
| 핀 2 | 1B — Gate 1 input B |
| 핀 3 | NC — Not connected (per datasheet) |
| 핀 4 | 1C — Gate 1 input C |
| 핀 5 | 1D — Gate 1 input D |
| 핀 6 | NC — Not connected (per datasheet) |
| 핀 7 | GND — Ground |
| 핀 8 | 1Y — Gate 1 output |
| 핀 9 | NC — Not connected (per datasheet) |
| 핀 10 | 2A — Gate 2 input A |
| 핀 11 | 2B — Gate 2 input B |
| 핀 12 | 2C — Gate 2 input C |
| 핀 13 | 2D — Gate 2 input D |
| 핀 14 | VCC — Power supply, 2 V to 6 V |
일반적인 애플리케이션
SN74HC21DR 적합 용도: 6 애플리케이션s: Safety Interlock Logic, Address Decoding and Chip Select, Embedded System Glue Logic, Automotive Control Modules, Test and Measurement Instrumentation, Consumer Appliance Control Boards.
Safety Interlock Logic
Industrial machine guards, emergency-stop chains, and access panels frequently require that ALL sensor conditions be satisfied before a machine can run - exactly the Boolean AND function the SN74HC21DR provides. Each 4-input gate can combine up to four discrete limit-switch, relay, or optocoupler signals into a single enable signal at a deterministic 11 ns propagation delay, with no firmware, no programming, and no boot time. The 2 V to 6 V supply tolerance handles noisy industrial rails, and the 5.2 mA output drive directly interfaces PLC inputs and opto-isolators. Because logic is implemented in silicon rather than a microcontroller, the interlock path remains valid even during MCU reset or fault conditions, which safety assessors favor.
추천
Address Decoding and Chip Select
In microprocessor and memory-mapped systems, chip-select generation often requires ANDing several address lines with control strobes. The SN74HC21DR's two independent 4-input gates decode combinations such as address-range bits plus a read/write strobe in a single 14-pin package, replacing multiple discrete gates. The 11 ns typical propagation delay at 5 V adds minimal latency to memory access timing, and the ±4 mA output drive at 5 V meets TTL-level load requirements on bus-oriented boards. Input clamp diodes allow interfacing to signals slightly above VCC via current-limiting resistors, useful in mixed-supply legacy systems. At 20 uA maximum quiescent current it adds negligible standby load to always-on decoder rails.
추천
Embedded System Glue Logic
Board bring-up and mixed-signal designs routinely need a handful of random logic functions to gate resets, combine enable signals, or qualify interrupts. The SN74HC21DR is a staple glue-logic choice: two 4-input AND gates in SOIC-14 cost about $0.14 at 1k pieces (as of 2026-09-04) and operate from the same 3.3 V or 5 V rail as the MCU. The CMOS inputs draw only 1 uA max, so pull-up networks can use high resistance values without loading, and the push-pull outputs swing rail-to-rail for clean input thresholds on downstream devices. Its -40C to +85C rating covers most embedded operating environments without derating.
추천
Automotive Control Modules
For automotive ECUs and body-control modules, the drop-in AEC-Q100-qualified sibling SN74HC21QDRQ1 (identical function and footprint) enables multi-condition gating such as ignition-on AND park-brake AND sensor-valid AND driver-command. Using dedicated AND gates rather than MCU firmware for precondition checks keeps critical gating deterministic and immune to software hangs. The 2 V to 6 V supply range tolerates load-dump-affected 12 V rails after regulation, and the -40C to +125C automotive grade covers underhood temperatures. Outputs at 5.2 mA drive fan-out to multiple diagnostic inputs, and the SOIC-14 footprint is proven in high-vibration assemblies.
추천
Test and Measurement Instrumentation
Bench instruments, trigger circuits, and event counters use wide-input AND gates to qualify events: for example, triggering a capture only when four simultaneous conditions (arm, level-cross, window-valid, and strobe) are true. The SN74HC21DR's fast 11 ns typical propagation delay preserves timing resolution, while CMOS symmetry keeps duty-cycle distortion low. Input clamp diodes protect against overrange probe conditions when series resistors are fitted, and the low 20 uA supply current suits battery-powered portable instruments. Standardized SOIC-14 hand-solderable footprint eases prototyping and rework during instrument calibration and board-level service.
추천
Consumer Appliance Control Boards
Washers, HVAC controllers, and kitchen appliances combine door-closed, water-level, temperature-ok, and user-enable signals before actuating motors or heaters - a textbook 4-input AND application. The SN74HC21DR gives designers a $0.14 (at 1k, as of 2026-09-04) hardware gate whose output directly drives triac-driver or relay-driver inputs at 5.2 mA. Operation down to 2 V supports battery-backed or brown-out-tolerant supplies, and RoHS compliance meets global appliance regulations. Implementing safety-relevant gating in hardware rather than firmware simplifies compliance documentation and adds a layer independent of the main MCU.
추천
추천 제품 요약
엔지니어링 참조 데이터: SN74HC21DR — 비교, 설계 지침 및 규정 준수 정보.
선택 가이드
대체품과의 비교
| 파라미터 | 이 제품 | SN74HC21QDRQ1 | CD74HC21M96 | M74HC21RM13TR | HD74HC21RP-EL | SN74HC21QPWRQ1 |
|---|---|---|---|---|---|---|
| Package | SOIC-14 (D) | SOIC-14 (D) - same | SOIC-14 - same | SO-14 - same footprint | SOP-14 - same footprint | TSSOP-8 - different |
| Brand | Texas Instruments | Texas Instruments | Texas Instruments (Harris line) | STMicroelectronics | Renesas Electronics | Texas Instruments |
| Supply Voltage Range | 2 V to 6 V | 2 V to 6 V | 2 V to 6 V | 2 V to 6 V | 2 V to 6 V | 2 V to 6 V |
| AEC-Q100 Qualification | No | Yes | No | No | No | Yes |
| Function | Dual 4-input positive-AND | Dual 4-input positive-AND | Dual 4-input positive-AND | Dual 4-input positive-AND | Dual 4-input positive-AND | Dual 4-input positive-AND |
주요 차별점
- Standard industrial grade with lowest cost (vs SN74HC21QDRQ1)
- Ultra-low static power (vs DM74ALS21AM (bipolar LS/ALS family))
- Wide 2 V to 6 V supply range (vs DM74ALS21AM)
설계 노트
Never leave any of the four inputs of an HC-family AND gate floating. Unused inputs must be tied to VCC (for AND gates, floating-high is required functionally, but a hard tie is mandatory for noise immunity) or GND. A floating CMOS input hovers near the switching threshold, draws shoot-through current, can raise ICC from 20 uA to several mA, and picks up noise that glitches the output. On SOIC-14, pins 3, 6, and 9 are NC and must not be used as tie points.
Decouple VCC (pin 14) with a 100 nF ceramic capacitor placed within a few millimeters of the pin, plus bulk capacitance per board convention. Although the 20 uA static ICC is tiny, CMOS shoot-through during the ~11 ns output transitions creates nanosecond current spikes; without local decoupling these inject ground bounce into shared analog or clock rails. On multi-gate boards, one 100 nF per package plus one 10 uF per region is the standard practice per TI HC-family application guidance.
CMOS inputs include clamp diodes to VCC and GND, allowing inputs above VCC only through a series current-limiting resistor (keep injected current within the datasheet limit). When gating slow, noisy signals such as relay or limit-switch contacts, add an RC filter plus a Schmitt-trigger buffer (e.g., SN74HC14) ahead of the AND inputs; the HC21 input has no hysteresis, and slowly rising edges near the threshold can cause output chatter and multiple transitions.
규정 준수 정보
RoHS-compliant lead-free SOIC (D) package per TI standard production. Not AEC-Q100 qualified - use SN74HC21QDRQ1 for automotive. REACH and halogen-free declarations: confirm on TI Quality & Environmental page.
