Texas Instruments CD40147BM

Overview

CD40147BM from Texas Instruments is a CMOS 10-line-to-4-line priority encoder IC that converts active-high decimal inputs (0–9) into active-low BCD outputs (8, 4, 2, 1), with input line 9 assigned highest priority. It operates over –55°C to +125°C, features buffered TTL-compatible outputs (driving one LSTTL load), and exhibits logic-1 output state (VSS) when all inputs are low. Used in keyboard encoding and interrupt prioritization circuits where deterministic highest-priority resolution is required.

For engineers reviewing the CD40147BM datasheet, CD40147BM pinout, CD40147BM application, or CD40147BM equivalent, key selection considerations include its priority encoding behavior, active-low BCD output polarity, SOIC-16 package compatibility, and functional equivalence to TTL 74147 when pin 15 is grounded - critical for legacy system upgrades and mixed-technology interface design.

Technical Context

The CD40147BM implements a fixed-priority combinational logic encoder with no internal latching or clocking; encoding occurs asynchronously on input state change. Its priority resolution ensures only the highest-numbered asserted input (0–9) determines the BCD output, suppressing lower-priority assertions regardless of simultaneous activation.

All ten inputs and four outputs are fully buffered with CMOS-level drive strength and TTL-compatible voltage thresholds. Output logic levels are active-low: '0' = V_DD, '1' = V_SS; thus, unasserted (all-inputs-low) condition yields 1111_BCD at outputs - a defined idle state distinct from encoded zero (0000_BCD).

Key Specifications

Pinout & Package

CD40147BM is housed in a 16-pin SOIC (Small Outline Integrated Circuit) package (TI package code D), measuring 10.3 mm × 5.3 mm × 1.75 mm, with gull-wing leads and 1.27 mm pitch. The package is RoHS-compliant, lead-finished with NiPdAu, and rated MSL Level-1 (unlimited floor life at ≤30°C/60% RH).

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar priority encoder applications.

Compared with CD40147BE and 74HC147, the CD40147BM uniquely combines SOIC-16 packaging, –55°C to +125°C operation, guaranteed 1111 idle output, and 3–18 V flexibility - making it the optimal choice for ruggedized, mixed-voltage, and high-reliability priority encoding where layout density and thermal performance matter.

Availability

CD40147BM is available at Aetrix Electronics and suitable for industrial control panels, legacy system upgrades, and embedded interrupt management requiring stable component supply, long-term lifecycle assurance, and RoHS-compliant sourcing.

Supply support for CD40147BM 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

Texas Instruments is a global semiconductor company headquartered in Dallas, Texas, delivering analog and embedded processing solutions for industrial, automotive, and personal electronics markets.

The CD40147BM belongs to TI's legacy CMOS 4000-series logic family, designed specifically for robust, low-power, wide-supply-voltage digital interfacing in harsh environments and mixed-technology systems.

FAQ

What is the function of pin 15 on the CD40147BM?

Pin 15 on the CD40147BM is a no-connect (NC) terminal. Texas Instruments specifies it as internally unused; it must remain unconnected or grounded per design guidelines to prevent noise coupling into the IC. Unlike the TTL 74147, the CD40147BM does not require pin 15 to be tied low for functional equivalence - that requirement applies only when emulating 74147 behavior in mixed-technology systems, not to the CD40147BM's native operation.

Does the CD40147BM support 3.3 V operation?

Yes, the CD40147BM supports 3.3 V operation within its specified 3 V to 18 V supply range. At 3.3 V, it meets all AC and DC parametric limits in the datasheet, including propagation delay (typically 120 ns max), output drive capability, and input threshold compatibility. This makes the CD40147BM suitable for mixed-voltage systems interfacing with 3.3 V microcontrollers while retaining full functionality - unlike 74HC-series encoders limited to 2–6 V.

How does the CD40147BM handle multiple simultaneous inputs?

The CD40147BM resolves multiple simultaneous inputs using fixed hardware priority: input I9 has highest priority, followed by I8 down to I0. When two or more inputs are high, only the highest-numbered active input determines the BCD output; lower-priority inputs are ignored. This priority encoding is implemented in combinational logic with no clocks or latches, ensuring deterministic, race-free output generation - a core feature confirmed in the Harris/TI datasheet truth table and functional description.

What is the output state of the CD40147BM when all inputs are low?

When all ten inputs (I0–I9) are low, the CD40147BM drives all four BCD outputs (O8, O4, O2, O1) to logic high (V_SS), resulting in the 1111_BCD state. This defined idle output is explicitly documented in the datasheet and distinguishes the CD40147BM from non-priority encoders or variants lacking guaranteed quiescent behavior - enabling reliable "no key pressed" or "no interrupt pending" detection in real-world systems.

Is the CD40147BM pin-compatible with the 74147 TTL encoder?

The CD40147BM is not pin-compatible with the 74147 due to differing pinouts: 74147 uses a 16-pin package but assigns V_CC to pin 16 and GND to pin 8, whereas CD40147BM places V_DD at pin 16 and V_SS at pin 11. However, the CD40147BM is functionally equivalent to the 74147 when pin 15 is grounded - matching truth tables and active-low BCD output behavior - making it a drop-in functional replacement in many designs with minor PCB modification.