High Voltage CMOS Logic ICs <Function Logic># Technical Documentation: BU4028B BCD-to-Decimal Decoder / Driver
Manufacturer : ROHM Semiconductor
Document Version : 1.0
Classification : Integrated Circuit (IC) - Logic Device
---
## 1. Application Scenarios
### 1.1 Typical Use Cases
The BU4028B is a monolithic silicon-gate CMOS integrated circuit that functions as a BCD-to-Decimal decoder or a binary-to-octal decoder . Its primary function is to convert a 4-bit Binary Coded Decimal (BCD) input into one of ten mutually exclusive decimal outputs (active HIGH). When used in its secondary mode, it can decode a 3-bit binary input into one of eight octal outputs.
Primary Applications Include:
* Display Driving: Directly driving low-current LED, incandescent, or fluorescent display segments in numeric readouts, where each output corresponds to a digit (0-9). Its active HIGH outputs are suitable for common-cathode displays.
* Industrial Control Systems: Selecting one of ten channels or devices in automated control panels, test equipment, and process control systems based on a BCD control signal from a microprocessor or counter.
* Address Decoding: In simpler digital systems or as a secondary address decoder in memory-mapped I/O, where a BCD address needs to enable one specific device or memory block.
* Keyboard Encoder Interfaces: Converting column/row scan codes into a singular output line for further processing in input subsystems.
* Sequential Machine Control: Acting as the output stage in state machines or sequencers where each state (0-9) enables a specific action or subsystem.
### 1.2 Industry Applications
* Consumer Electronics: Used in vintage digital clocks, timers, appliance control panels, and basic electronic toys featuring numeric displays.
* Test & Measurement Equipment: Found in digital multimeters, frequency counters, and signal generator display units for numeric output decoding.
* Industrial Automation: Employed in panel meters, batch counters, and simple programmable logic controller (PLC) output modules for channel selection.
* Telecommunications: Historically used in switching equipment and channel selectors. Modern use is limited to legacy system maintenance.
* Automotive: Applicable in older dashboard instrumentation clusters for gear position or trip computer readouts (subject to extended temperature grade requirements).
### 1.3 Practical Advantages and Limitations
Advantages:
* Simplified Design: Reduces component count compared to implementing decoding logic with discrete gates.
* CMOS Technology: Features very low static power consumption, high noise immunity (~45% of supply voltage), and a wide operating voltage range (3V to 18V).
* Direct Drive Capability: Outputs can source/sink sufficient current (typically > 1mA at 10V VDD) to drive LEDs or high-impedance loads directly, simplifying display interfaces.
* Uncomplicated Interface: Straightforward BCD input to 1-of-10 output mapping, easy to integrate with counters (e.g., 4029, 4510) and microcontrollers.
Limitations:
* Limited Drive Current: For driving standard LEDs or relays, external buffer transistors (e.g., ULN2003) are almost always required, adding to board space and cost.
* Active HIGH Outputs: Inherently suited for common-cathode displays. Driving common-anode displays requires inverting buffers, adding complexity.
* Speed: As a 4000-series CMOS part, its operational speed (propagation delay ~300ns typical at 10V) is not suitable for high-frequency applications (> few MHz).
* Modern Obsolescence: For new designs, dedicated display driver ICs (with multiplexing, latch, and higher drive) or microcontroller-based software
