CD4543 — BCD-to-7-Segment Latch/Decoder/Driver for LCD & LED

Overview

The CD4543 (CD4543B / HEF4543B) is a versatile BCD-to-7-segment latch/decoder/driver IC manufactured by Texas Instruments, ON Semiconductor, and Renesas. Unlike the CD4511 (which is restricted to active-HIGH common-cathode LEDs), the CD4543 includes a Phase control input (PH), allowing it to drive Liquid Crystal Displays (LCDs), common-anode LEDs, or common-cathode LEDs.

Operating over 3.0V to 18.0V DC, the CD4543 converts a 4-bit BCD input ( $A, B, C, D$ ) into a 7-segment display pattern ( $a \dots g$ ). When driving reflective LCD panels, an external AC square wave signal (typically $50\text{ Hz} \dots 100\text{ Hz}$ ) is applied simultaneously to the LCD backplane and the PH pin, providing true AC drive to prevent LCD electrochemical degradation.

Quick reference


Supply Voltage (`VDD - VSS`)	3.0 V to 18.0 V DC
Input Format	4-bit BCD ( $A, B, C, D$ )
Display Outputs	7 Phase-Controlled outputs ( $a \dots g$ )
Display Types Supported	LCD Displays (AC Drive), Common-Cathode LEDs, Common-Anode LEDs
Control Features	Latch Disable ( $LD$ ), Blanking ( $BL$ ), Phase Control ( $PH$ )
Package	16-pin DIP / SOIC-16

Pinout (DIP-16 Package)

text

             ┌───┴───┐
         LD 1│ 1   16│ VDD (+3V to +18V)
          B 2│       │15 g
          C 3│ CD4543│14 f
          D 4│       │13 e
          A 5│       │12 d
         PH 6│       │11 c
         BL 7│       │10 b
   VSS(GND) 8│       │9  a
             └───────┘

Pin	Name	Type	Description
1	`LD`	Input	Latch Disable Input (High = Pass-through BCD data; Low = Latch stored BCD value)
2	`B`	Input	BCD Bit 1 Input ( $2^1 = 2$ )
3	`C`	Input	BCD Bit 2 Input ( $2^2 = 4$ )
4	`D`	Input	BCD Bit 3 Input ( $2^3 = 8$ , MSB)
5	`A`	Input	BCD Bit 0 Input ( $2^0 = 1$ , LSB)
6	`PH`	Input	Phase Control Input (Connect to AC square wave for LCD backplane, GND for CC LEDs, VDD for CA LEDs)
7	`BL`	Input	Blanking Input (Active HIGH: High = Turn OFF all segments; Low = Enable display)
8	`VSS`	Power	Digital Ground (0 V)
9–15	`a, b, c, d, e, f, g`	Output	7-Segment Driver Outputs
16	`VDD`	Power	Positive Power Supply (+3.0V to +18.0V DC)

Phase Pin Configuration Matrix

Target Display Type	`PH` (Pin 6) Connection	Output Logic Level
Common-Cathode LED	Connect `PH` to GND	Active-HIGH ( $a \dots g$ HIGH turns segment ON)
Common-Anode LED	Connect `PH` to `VDD`	Active-LOW ( $a \dots g$ LOW turns segment ON)
Reflective LCD Panel	Connect `PH` & LCD Backplane to 50Hz Square Wave	Out-of-phase AC square wave drives segment ON

Common mistakes

Connecting DC directly to reflective LCD glass: Direct DC voltage across liquid crystal segments destroys the panel via electrolysis. Always apply an AC square wave to the PH pin and LCD backplane.
Forgetting that LD pin logic is inverse to CD4511 LE: On the CD4543, LD is Latch Disable (HIGH = real-time count; LOW = latched memory). On the CD4511, LE is Latch Enable (LOW = real-time count; HIGH = latched memory).

Notes

CD4543 vs CD4511: CD4543 supports LCD panels and common-anode LEDs via phase inversion; CD4511 is limited to active-HIGH common-cathode LEDs.