• [ CXLE88171 ]"

Ordering

Introduction

            In modern electronic display systems, LED driver chips play a central role. CXLE88171, as a constant current LED driver control dedicated circuit that integrates a keyboard scanning interface, is widely used in various segment code LED displays due to its high performance, high reliability, and flexible configurability. This article will provide a comprehensive analysis of the technical characteristics, working principle, instruction system, electrical parameters, and typical application circuits of CXLE88171, providing engineers and electronics enthusiasts with a comprehensive reference.obf嘉泰姆

1、 Chip Overview

          CXLE88171 is manufactured using power CMOS technology and integrates MCU digital interfaces, data latches, high-voltage LED driver circuits, and keyboard scanning modules internally. Its packaging form is SOP32, suitable for various LED display scenarios, supporting 11 segments× 7 to 14 segments× Flexible display mode with 4 digits. The chip has excellent constant current output characteristics, and the current error between channels does not exceed± 3%, with inter chip error not exceeding± 6% to ensure display uniformity.obf嘉泰姆

2、 Main characteristics

▲ Diverse display modes: Supports 11× 7、12× 6、13× 5、14× Multiple combinations of levels 4.obf嘉泰姆

▲ Constant current driveThe maximum output voltage of SEG port can reach VDD-1V, and it supports 8-level software adjustable brightness.obf嘉泰姆

▲ Keyboard scanning functionProvide 10× 3 matrix keyboard scanning interface, automatically completes key value collection.obf嘉泰姆

▲ Communication interfaceSupports four wire serial communication (CLK, STB, DIN, DOUT) and is compatible with multiple MCUs.obf嘉泰姆

▲ Built in RC oscillatorThe frequency is 450kHz± 5%, no need for external crystal oscillator.obf嘉泰姆

▲ Packaging and Power SupplySOP32 packaging, working voltage 5V± 10%, built-in power on reset circuit.obf嘉泰姆

3、 Detailed explanation of pin functions

symbol

pin name

Pin number

Instructions

DOUT

data output

two

Output serial data on the falling edge of the clock, starting from the lower bits. N-tube leakage output. If DIN and DOUT use the same level, they can be short circuited with DIN for DIN/DOUT multiplexing.

DIN

data input

three

Input serial data on the rising edge of the clock, starting from the lower bits. If DIN and DOUT use the same level, they can be short circuited with DOUT for DIN/DOUT multiplexing.

CLK

Clock input

four

Read serial data on the rising edge and output data on the falling edge

STB

Film selection input

five

Initialize the serial interface on the rising or falling edge, and then wait for the instruction to be received. The first byte after the low value of STB is used as an instruction, and when processing the instruction, other current processing is terminated. When STB is high, CLK is ignored

NC

NC

1. 13

Internal unconnected

K1～K3

Key scan data input

6~8

The data input for this foot is latched after the display cycle ends

SGE1/KS1～ SEG8/KS8

Output (segment)

10~12obf嘉泰姆 14~18

Constant current output (also used for key scanning), p-tube open drain output

SEG9~SEG11

Output (segment)

19-21

Constant current output, P tube leakage output

GRID1～ GRID4

Output (bit)

27~32

Bit output, N-tube open leak output

SEG12/DRID7 ～obf嘉泰姆 SEG14/GRID5

Output (segment/bit)

22~24

Segment/bit multiplexing output, can only select segment or bit output

VDD

Logic power supply

9. 25

5V± 10%

GND

Logically speaking

26, 29, 32

Grounding system

▲   Note:When the DOUT port outputs data, it is an N-tube open drain output. When reading keys, an external pull-up resistor of 1K-10K is required, as shown in Figure (1). thisobf嘉泰姆
The company recommends a 10K pull-up resistor. DOUT controls the action of N tube on the falling edge of the clock, and the reading is unstable at this time. You can refer to Figure (6),obf嘉泰姆
The reading only stabilizes at the rising edge of the clock.

The 32 pins of CXLE88171 include power, ground, segment/bit output, key scan input, and communication interface. among whichobf嘉泰姆

▲SEG1~SEG11Constant current output, used to drive LED segment codes, with P tube leakage output.obf嘉泰姆

▲GRID1~GRID7Bit output, N-tube open drain output, used for scanning display bits.obf嘉泰姆

▲K1~K3Key scan data input, combined with SEG/KS multiplexing port to achieve 10× 3 keyboard matrix.obf嘉泰姆

▲DIN/DOUT: Supports data reuse, requires external 10kΩ Pull up the resistor to ensure read key stability.obf嘉泰姆

4、 Display and Key Scan Register Structure

        The chip contains a 14 byte display register with addresses ranging from 00H to 0DH, each corresponding to an LED segment code. Data writing should be performed in the order of low address to high address and low bit to high bit. The key scan data register consists of 5 bytes (BYTE1~BYTE5), with each byte containing 6 valid key value bits. It supports multi key detection and combination key recognition, but it should be noted that only keys under the same K-line can form a combination key.obf嘉泰姆

4.2. Key Scan and Key Scan Data Registerobf嘉泰姆
The key scan matrix is 10× 3bit， As shown in Figure (3):obf嘉泰姆
obf嘉泰姆
        The key scan data storage address is shown in Figure (4). After issuing the read key command, start sequentially reading the key data BYTE1— BYTE5 bytes, read dataobf嘉泰姆
Starting from the low bits, where B6 and B7 are invalid bits, the chip output is 0. When the buttons corresponding to the K and KS pins of the chip are pressed, the correspondingobf嘉泰姆
The BIT within the byte is 1.obf嘉泰姆

▲ Note: 1. CXLE88171 can read a maximum of 5 bytes and does not allow multiple reads.obf嘉泰姆
2. Read data bytes can only be read sequentially from BYTE1-BYTE5 and cannot be read across bytes. For example, on the hardware, K2 corresponds to KS10obf嘉泰姆
When the key is pressed, in order to read the data of this key, it is necessary to read the 4th BIT bit of the 5th byte before reading the data;obf嘉泰姆
When the three buttons K1 and KS10, K2 and KS10, and K3 and KS10 are pressed simultaneously, the B3, B4, and B5 bits of the data read by BYTE5 are all 1 (BYTE5 );obf嘉泰姆
= #38H）。obf嘉泰姆
3. Combination keys can only be the same KS, and different K pins can be used as combination keys; The same K and different KS pins cannot be combinedobf嘉泰姆
Key usage.obf嘉泰姆

5、 Detailed Explanation of Instruction System

        If the STB is set to a high level during instruction or data transmission, serial communication is initialized, and the instruction or data being transmitted is invalidobf嘉泰姆
The instructions or data transmitted in advance remain valid.obf嘉泰姆
CXLE88171 achieves functional configuration through four instructions:obf嘉泰姆

5.1. Display Mode Setting Command(B7B6=00): Set the number of segments and bits. After execution, it will display as closed and needs to be restarted.obf嘉泰姆

B7

B6

B5

B4

B3

B2

B1

B0

function

Instructions

0

one

Unrelated item, fill in 0

0

0

Data read-write mode setting

Write data to the display register

0

one

one

0

Read key to scan data

0

one

0

Address increase mode setting

Address automatically increases

0

one

one

fixed address

0

one

0

Test mode setting
(For internal use)

Normal Mode

0

one

one

test mode

5.3. Address Setting Command(B7B6=11): Set the starting address of the display register.obf嘉泰姆

5.4. Display Control Commands(B7B6=10): Control display switch and constant current ratio (adjustable from 1/16 to 14/16).obf嘉泰姆

6、 Serial communication timing sequence

              The data is input at the rising edge of CLK and output at the falling edge. STB is the chip selection signal, and its falling edge marks the start of the instruction. When reading the key, wait for at least 1μ s after the 8th rising edge of CLK before reading the data to ensure stability. Supports two data transmission modes: automatic address addition and fixed address, to meet different application needs.obf嘉泰姆

obf嘉泰姆
▲ Attention:When reading data, an equal interval is required between setting instructions from the 8th rising edge of the serial clock CLK and reading data from the falling edge of CLKobf嘉泰姆
Wait for Twait (minimum 1μ S).obf嘉泰姆

7、 Display and button application examples

7.1. Common cathode digital tube driver:Taking GRID1 as an example, if the number is displayed as“ 0” Write 3FH (binary 00111111) at address 00H, corresponding to SEG1~SEG6 high level and SEG7 low level.obf嘉泰姆

obf嘉泰姆
Figure 7 shows the schematic diagram of the connection of the common cathode digital tube. If the digital tube displays“ 0” Then you need to let go when GRID1 is at a low levelobf嘉泰姆
SEG1, SEG2, SEG3, SEG4, SEG5, SEG6 are at high level, and SEG7 is at low level.obf嘉泰姆
To view the address table shown in Figure (2), simply write data 3FH in the 00H address unit to make the digital display“ 0”。obf嘉泰姆

7.2. Gongyang Digital Tube Driver:Segment code data needs to be written separately in multiple GRID address units, such as address 01H for 00H, 02H, etc., and 00H for the rest.obf嘉泰姆

obf嘉泰姆

        Figure 8 shows the schematic diagram of the connection of the Gongyang digital tube. If the digital tube displays“ 0” Then you need to go to Grid1, Grid2, Grid3, Grid4,obf嘉泰姆
When GRID5 and GRID6 are low, let SEG1 be high, and when GRID7 is low, let SEG1 be low. To address unit 00H,obf嘉泰姆
Write data 01H in 02H, 04H, 06H, 08H, and 0AH respectively, and write data 00H in all other address units.obf嘉泰姆

7.3. Button detection:The key scan is automatically completed by the chip, and users only need to read the key values in chronological order. If multiple keys are pressed simultaneously, multiple bits will be marked as“ in the key value register; 1”。obf嘉泰姆

    Key scanning is automatically completed by CXLE88171 and is not controlled by the user. Users only need to read key values in chronological order. Completing a key scan requires 2 displaysobf嘉泰姆
Cycle, one display cycle requires approximately T=8× 500us， Two different keys were pressed in 8MS, and the key values read twice were both pressed firstobf嘉泰姆
The key value of that button.obf嘉泰姆
Observe the output key scan waveforms of SEG1/KS1 and SEG2/KS2 using an oscilloscope according to Figure (9), as shown in Figure (10).obf嘉泰姆

obf嘉泰姆
The waveform of SEGn/KSn during keyboard scanning of IC:obf嘉泰姆

obf嘉泰姆

The oscillation frequency of Tdisp and IC operation is related, and 500us is for reference only. Actual measurements shall prevail.obf嘉泰姆
In general, using Figure (11) can meet the requirements of button design.obf嘉泰姆

obf嘉泰姆

When S1 is pressed, read 'B0' in the first byte; 1”。 If multiple buttons are pressed, multiple“ will be read; 1” When S2,obf嘉泰姆
When S3 is pressed, it can be read from B1 and B3 in the first byte; 1”。obf嘉泰姆
▲ Attention:Precautions for using composite keys:obf嘉泰姆
SEG1/KS1-SEG10/KS10 are multiplexed for display and key scanning. Taking Figure (12) as an example, the display requires D1 to be on and D2 to be off, and SEG1 needs to be activatedobf嘉泰姆
For“ 1” ，   SEG2 is“ 0” If S1 and S2 are simultaneously pressed, it is equivalent to SEG1 and SEG2 being short circuited, and D1 and D2 are both illuminated.obf嘉泰姆

obf嘉泰姆

Solution:obf嘉泰姆
1. In terms of hardware, the keys that need to be pressed simultaneously can be set on different K-lines as shown in Figure (13).obf嘉泰姆

obf嘉泰姆

2. In SEG1‐ The series resistor on SEG N is shown in Figure (14), and the resistance value of the resistor should be selected at 510 ohms. If it is too high, it will cause the button to fail,obf嘉泰姆
Too small may not solve the problem of display interference.obf嘉泰姆

obf嘉泰姆

3. Or connect diodes in series as shown in Figure (15).obf嘉泰姆

obf嘉泰姆

7.4. Serial data transmission during applicationobf嘉泰姆

7.4.1) Automatic address plus one modeobf嘉泰姆
        Using the address auto increment mode, setting the address is actually setting the starting address for storing the transmitted data stream. The starting address command word has been sentobf嘉泰姆
Done,“ STB” There is no need to set the height to closely follow the data transmission, up to 14BYTE, and only after the data transmission is completed will it be sent; STB” Set high.obf嘉泰姆
obf嘉泰姆
Command1: Display Mode Setting Commandobf嘉泰姆
Command2: Data read/write setting commandobf嘉泰姆
Command3: Display Address Setting Commandobf嘉泰姆
Data1~n: Display data, starting from the address specified in Command3 (up to 14 bytes)obf嘉泰姆
Command4: Display control commandsobf嘉泰姆
7.4.2)Fixed address modeobf嘉泰姆
Using the fixed address mode, setting the address is actually setting the address where the 1BYTE data to be transmitted is stored. The address has been sent,“ STB”obf嘉泰姆
No need to set it high, immediately transmit 1BYTE data, and only after the data transmission is completed will it be sent; STB” Set high. Then reset the location where the second data needs to be storedobf嘉泰姆
Address, up to 14BYTE data transmission completed,“ STB” Set high.obf嘉泰姆
obf嘉泰姆
Command1: Display Mode Setting Commandobf嘉泰姆
Command2: Data read/write setting commandobf嘉泰姆
Command3: Display Address Setting Command, Set Display Address 1obf嘉泰姆
Data1:   Display data 1 and store it in the address unit specified by Command3obf嘉泰姆
Command4: Display Address Setting Command, Set Display Address 2obf嘉泰姆
Data2:   Display data 2 and store it in the address unit specified in Command4obf嘉泰姆
Command5: Display Control Commandsobf嘉泰姆
7.4.3) Read button timing sequenceobf嘉泰姆
obf嘉泰姆
Command1: Read key commandsobf嘉泰姆
Data1-5: Read key dataobf嘉泰姆
7.4.4) Program Designobf嘉泰姆

7.4.4.1) Program flow chart of automatic address plus one mode:obf嘉泰姆

obf嘉泰姆

7.4.4.2) Flowchart of program design using fixed addresses:obf嘉泰姆

obf嘉泰姆

8、 Constant current control and heat dissipation design

              The constant current output of CXLE88171 remains stable when VDS<4V, with a typical output current of 35mA. The actual power consumption needs to meet:obf嘉泰姆

PD(act)=IDD​× VDD​+IOUT​× VDS​× Duty× elevenobf嘉泰姆

It is necessary to ensure that the actual power consumption is less than the maximum allowable power consumption, and to control the temperature rise of the chip through thermal design.obf嘉泰姆
8.1. Constant current control circuitobf嘉泰姆
CXLE88171 supports constant current driver applications for use in high-end display drivers.obf嘉泰姆
1. The maximum current error between channels is less than± 3 ℅, and the maximum current error between chips is less than± 6%.obf嘉泰姆
When operating in a constant current linear region, it is necessary to ensure that the voltage difference between the SEG pin and GND is less than 4V.obf嘉泰姆
3. In addition, when the load side voltage (VDS) changes, the stability of its output current is not affected, as shown in the following figure:obf嘉泰姆

obf嘉泰姆

Package heat dissipation power (PD)obf嘉泰姆
        The maximum heat dissipation power of the package is determined by the formula:obf嘉泰姆

obf嘉泰姆
It was decidedobf嘉泰姆
When all 11 channels are fully open, the actual power consumption is:obf嘉泰姆
obf嘉泰姆
The actual power consumption must be less than the maximum power consumption, that is  To maintainMaximum output powerobf嘉泰姆
The relationship between current and constant current ratio is:obf嘉泰姆
obf嘉泰姆

Among them, Tj is the operating temperature of the IC, Ta is the ambient temperature, V is the voltage of the stable current output port, Duty is the constant current ratio of 14/16,obf嘉泰姆
DSRth (j-a) is the thermal resistance of the package.obf嘉泰姆

9、 Typical Application Circuit

9.1. Common Yin Connection Scheme:SEG port is connected to the LED anode, GRID port is connected to the cathode, and communicates with MCU through DIN, CLK, and STB. DOUT can be reused as input.obf嘉泰姆

obf嘉泰姆

9.2. Common Yang Connection Scheme:Reverse the voltage configuration and connect 510&Omega in series at the SEG port; Resistors or diodes prevent display interference.obf嘉泰姆

obf嘉泰姆
▲ Attention:1. The filtering capacitor between VDD and GND should be placed as close as possible to the CXLE88171 chip on the PCB board to enhance the filtering effect.obf嘉泰姆
2. Four 100P capacitors connected to DIN, DOUT, CLK, and STB communication ports can reduce interference to the communication ports.obf嘉泰姆
3. Due to the conduction voltage drop of the blue light digital tube being about 3V, the CXLE88171 should be powered with 5V.obf嘉泰姆
4. To enable the chip to enter the constant current linear working area, please ensure that the voltage drop between the SEG channel and GND is less than 4V.obf嘉泰姆

9.3 PCB Layout Suggestionsobf嘉泰姆

▲The filtering capacitor between VDD and GND should be close to the chip.obf嘉泰姆

▲Connect a 100pF capacitor in parallel with the communication line to suppress interference.obf嘉泰姆

▲Blue LED requires 5V power supply to ensure voltage drop requirements.obf嘉泰姆

10、 Electrical parameters and timing characteristics

▲Working Voltage：4.5V~5.5Vobf嘉泰姆

▲constant current output28mA~40mA (SEG port)obf嘉泰姆

▲Maximum clock frequency：1MHzobf嘉泰姆

▲Timing requirementsCLK pulse width≥ 400ns, STB pulse width≥ 1μ s， Data establishment/retention time: 100nsobf嘉泰姆
10.1. Limit parameters (Ta=25 ℃, VSS=0 V)obf嘉泰姆

11、 Conclusion

              CXLE88171 is an ideal choice for segment LED display and keyboard scanning applications due to its high integration, flexible configuration, and stable and reliable performance. Through reasonable circuit design and software control, it can be widely applied in industrial control, instrumentation, consumer electronics and other fields. The technical analysis and application guide provided in this article are hoped to provide strong support for your project development.obf嘉泰姆

TwelveSelection Guide for Related Chips;                       More similar products ....obf嘉泰姆

◀ Previous:CXLE88155N with keyboard scanning LED driver chip detailed explanation: features, instruction set, hardware design and application guide

Back to top

Next▶:CXLE88172 LED Driver Chip Data Sheet Detailed Explanation: Features, Pins, Timing, and Application Guide