Overview of the CD4511BE

The CD4511BE is a 16-pin DIP (Dual Inline Package) chip belonging to the 4000 series of CMOS logic ICs. Its primary function is to convert a 4-bit BCD input into the corresponding 7-segment display code and provide the necessary drive current to directly power a LED or LCD 7-segment display.

Some key characteristics of the CD4511BE include:

• Supply voltage range: 3V to 15V
• Low power consumption
• High noise immunity inherent to CMOS design
• 25mA output drive current capability
• 4-bit latch for storing BCD input
• Lamp test, blanking, and latch enable control inputs
• Available in DIP and SOIC surface mount packages

Pinout and Pin Functions

The CD4511BE comes in a 16-pin DIP or SOIC package. Here is the pinout diagram:

Pin	Name	Function
1	LE	Latch Enable
2	D1	BCD input D1
3	D2	BCD input D2
4	D3	BCD input D3
5	D4	BCD input D4
6	BL	Blanking control input (active low)
7	LT	Lamp test input (active low)
8	VSS	Ground
9	e	7-segment output e
10	d	7-segment output d
11	c	7-segment output c
12	b	7-segment output b
13	a	7-segment output a
14	g	7-segment output g
15	f	7-segment output f
16	VDD	Positive supply voltage

The functions of key pins are as follows:

• Latch Enable (LE): This active high input, when asserted, allows the BCD data on pins D1-D4 to be latched into the internal 4-bit storage register. When LE goes low, the last latched data is retained.

• BCD Inputs (D1-D4): These four inputs accept the binary coded decimal value to be displayed. D1 is the least significant bit (LSB).

• Blanking Input (BL): Driving this pin low causes all segment outputs to be turned off, effectively blanking the display while retaining the latched data.

• Lamp Test (LT): When driven low, this input overrides the latched BCD data and turns on all seven segment outputs, allowing quick testing of the display.

• Segment Outputs (a-g): These are active high outputs that drive the individual LED segments, labeled a through g, according to the standard 7-segment arrangement.

Applications

The CD4511BE is commonly used in a variety of applications requiring numeric displays, such as:

1. Digital clocks and timers
2. Instrumentation and measurement equipment
3. Counters and scoreboards
4. Digital thermometers and multimeters
5. Calculators and scales
6. Elevator floor indicators
7. Vending machines and arcade games

Its wide supply voltage range, low power consumption, and high output drive capability make it well-suited for battery-powered devices and systems with varying power supply rails.

Interfacing with a 7-Segment Display

The main application of the CD4511BE is driving a 7-segment common cathode LED display. Each segment of the display is illuminated by applying a logic high to the corresponding segment pin (a-g) of the CD4511BE.

To display a digit, the BCD code for that digit is applied to the D1-D4 inputs, and the LE pin is pulsed high to latch the data. The chip decodes the BCD value and activates the appropriate segment outputs. Current-limiting resistors, typically in the range of 100-220 ohms, are used in series with each segment to set the LED current.

Here’s a typical circuit for interfacing a CD4511BE with a common cathode 7-segment display:

        +--U1--+     
     a--| 13   |--R1--+
        |      |      |
     b--| 12   |      /
        |      |     /  
     c--| 11   |      |
        |      |     /
     d--| 10   |      \
        |      |      |
     e--|  9   |      /
        |      |     /
     f--| 15   |      |
        |      |     /
     g--| 14   |      \
        |      |      |
     DP-|      |      /
        |      |     | 
    VSS-|  8   |     |
        +------+     |
          |__|__GND  -
            ___  
 BL--|6   1|   |16|--VDD     
 LT--|7   2|   |15|--f
    -|8   3|   |14|--g  
 D1--|2   4|   |13|--a         
 D2--|3   5|   |12|--b
 D3--|4   6|   |11|--c
 D4--|5   7|   |10|--d
    -|    8|___|9 |--e

BCD to 7-Segment Decoder Logic

At the heart of the CD4511BE is the BCD to 7-segment decoder logic. It takes the 4-bit BCD input and activates the appropriate segment outputs to display the corresponding digit.

The decoding logic can be represented by the following truth table:

BCD Input (D4321)	Digit	a	b	c	d	e	f	g
0000	0	1	1	1	1	1	1	0
0001	1	0	1	1	0	0	0	0
0010	2	1	1	0	1	1	0	1
0011	3	1	1	1	1	0	0	1
0100	4	0	1	1	0	0	1	1
0101	5	1	0	1	1	0	1	1
0110	6	1	0	1	1	1	1	1
0111	7	1	1	1	0	0	0	0
1000	8	1	1	1	1	1	1	1
1001	9	1	1	1	1	0	1	1
1010	–	0	0	0	0	0	0	1
1011	–	1	0	0	1	1	1	1
1100	–	0	1	1	1	1	0	1
1101	–	1	0	0	1	1	0	1
1110	–	0	1	1	1	1	1	1
1111	–	0	0	0	0	0	0	0

Note that for BCD codes above 1001 (9), the decoder outputs are undefined and typically not used.

Output Latch and Control Inputs

In addition to the decoder logic, the CD4511BE incorporates a 4-bit output latch that stores the current BCD value. This allows the display to be updated without flickering by latching in a new value only when desired.

The latching action is controlled by the Latch Enable (LE) pin. When LE is high, the BCD input is transferred to the latch and the corresponding 7-segment code appears on the outputs. When LE goes low, the latch retains its current value regardless of changes on the BCD inputs.

Two additional control inputs, Blanking (BL) and Lamp Test (LT), are provided:

• Driving BL low turns off all segment outputs without affecting the contents of the latch. This is useful for creating blinking displays or multiplexing multiple digits.

• Pulling LT low overrides the latch and forces all segment outputs high, lighting up all segments of the display. This feature helps to quickly test the display for burned out segments.

Cascading Multiple CD4511BEs

For applications requiring multiple digits, CD4511BEs can be cascaded by connecting the BCD inputs in parallel and using separate LE signals for each chip.

Here’s an example circuit for a 4-digit display:

        +--U1--+           +--U2--+           +--U3--+           +--U4--+
     a--| 13   |--R1--+  a--| 13   |--R1--+  a--| 13   |--R1--+  a--| 13   |--R1--+
        |      |      |     |      |      |     |      |      |     |      |      |  
     b--| 12   |      /  b--| 12   |      /  b--| 12   |      /  b--| 12   |      /
        |      |     /      |      |     /      |      |     /      |      |     /
     c--| 11   |      |  c--| 11   |      |  c--| 11   |      |  c--| 11   |      | 
        |      |     /      |      |     /      |      |     /      |      |     /
     d--| 10   |      \  d--| 10   |      \  d--| 10   |      \  d--| 10   |      \
        |      |      |     |      |      |     |      |      |     |      |      |
     e--|  9   |      /  e--|  9   |      /  e--|  9   |      /  e--|  9   |      /
        |      |     /      |      |     /      |      |     /      |      |     /
     f--| 15   |      |  f--| 15   |      |  f--| 15   |      |  f--| 15   |      |
        |      |     /      |      |     /      |      |     /      |      |     /
     g--| 14   |      \  g--| 14   |      \  g--| 14   |      \  g--| 14   |      \
        |      |      |     |      |      |     |      |      |     |      |      |
     DP-|      |      /  DP-|      |      /  DP-|      |      /  DP-|      |      /
        |      |     |      |      |     |      |      |     |      |      |     |
    VSS-|  8   |     |  VSS-|  8   |     |  VSS-|  8   |     |  VSS-|  8   |     |
        +------+     |      +------+     |      +------+     |      +------+     |
          |__|__GND  -        |__|__GND  -        |__|__GND  -        |__|__GND  -
            ___              
           |   |  
 BL--|6   1|   |16|--VDD     
 LT--|7   2|   |15|--f
    -|8   3|   |14|--g  
 D1--|2   4|   |13|--a         
 D2--|3   5|   |12|--b
 D3--|4   6|   |11|--c
 D4--|5   7|   |10|--d
    -|    8|___|9 |--e

  LE1  LE2  LE3  LE4

By sequentially driving the LE pins of each CD4511BE, the display can be multiplexed to show a multi-digit value.

Driving Other Display Types

While the CD4511BE is designed for 7-segment common cathode displays, it can also be used with common anode displays by inverting the segment outputs with a CMOS hex inverter such as the CD4049.

For driving other display types like 14 or 16 segment alphanumeric displays, the CD4511BE can be used as a BCD to 7-segment decoder, with additional logic to map the 7-segment outputs to the target display.

Power Supply and Interfacing Considerations

The CD4511BE can operate from a supply voltage of 3V to 15V. The logic inputs are CMOS compatible, with a typical threshold of 1/2 VDD. Unused inputs should be tied to VDD or VSS to prevent floating pins.

When interfacing the CD4511BE with other logic families like TTL, level shifting may be necessary to ensure proper operation. In a mixed logic design, it’s important to verify that the output voltage levels of the driving device are compatible with the input thresholds of the CD4511BE.

Frequently Asked Questions

1. Q: What is the maximum supply voltage for the CD4511BE?
   A: The CD4511BE can operate with a supply voltage of up to 15V. However, the maximum voltage rating should not be exceeded to prevent damage to the device.

2. Q: How much current can each segment output of the CD4511BE sink?
   A: Each segment output of the CD4511BE can sink up to 25mA. This allows it to directly drive standard LED displays without the need for additional driver transistors.

3. Q: Can the CD4511BE be used with common anode displays?
   A: Yes, the CD4511BE can drive common anode displays by inverting its outputs using a CMOS hex inverter like the CD4049. The inverter should be powered from the same supply as the CD4511BE.

4. Q: What is the function of the Lamp Test (LT) pin on the CD4511BE?
   A: Pulling the LT pin low overrides the internal latch and forces all segment outputs high, lighting up all segments of the connected display. This feature allows quick testing for burnt out or disconnected segments.

5. Q: How can I multiplex a multi-digit display using CD4511BEs?
   A: To multiplex a multi-digit display, connect the BCD inputs of multiple CD4511BEs in parallel and drive their Latch Enable (LE) pins separately. By sequentially latching BCD values and enabling the corresponding digit, a multi-digit value can be displayed.

Conclusion

The CD4511BE is a versatile and widely used BCD to 7-