TLC5940NT

The TLC5940NT from Texas Instruments is a 16-channel constant-current sink LED driver with 12-bit (4096-step) grayscale PWM control and 6-bit (64-step) dot correction per channel. The dot correction compensates for brightness variations between individual LEDs and different driver ICs, and the correction data is stored in integrated EEPROM for automatic recall on power-up. A single external resistor on the IREF pin sets the maximum current for all 16 channels using the internal 1.24V bandgap reference (Imax = 1.24V / R_IREF × 31.5). The 12-bit grayscale PWM provides 4096 brightness levels per channel for smooth dimming and color mixing. The 30MHz serial interface supports daisy-chaining multiple TLC5940 devices through SIN/SOUT connections. Error detection includes LED Open Detection (LOD) and Thermal Error Flag (TEF), reported through the open-drain XERR pin that can be OR-ed across multiple ICs. The NT suffix denotes the 28-pin PDIP through-hole package.

The TLC5940NT operates as a constant-current sink driver where each of the 16 output channels sinks current from the LED anode supply (up to 17V) through the LED to ground. The maximum per-channel current is set by a single external resistor on the IREF pin: the internal 1.24V bandgap reference drives a current through R_IREF, which is then multiplied by 31.5 to set the maximum channel current. The 6-bit dot correction register (64 steps) scales this maximum current on a per-channel basis to compensate for LED brightness variations; this value is stored in EEPROM and automatically recalled on power-up. The 12-bit grayscale PWM register (4096 steps) controls the duty cycle of each channel’s output during each PWM period. The GSCLK pin provides the PWM clock, and the 12-bit counter counts from 0 to 4095 for each PWM cycle. The BLANK pin resets the counter and forces all outputs off. When BLANK goes low, the counter starts and each channel’s output turns on; when the counter value matches the channel’s grayscale value, that output turns off. The serial interface shifts data in through SIN on the rising edge of SCLK; the XLAT pin latches the data into the internal registers. Multiple devices are daisy-chained by connecting SOUT to the next device’s SIN. The LOD circuit detects when an output pin voltage is below the expected threshold (indicating an open or disconnected LED), and the TEF circuit detects overtemperature conditions. Both errors pull the open-drain XERR pin low.

• LED Video Walls: 12-bit grayscale (4096 levels) per channel provides smooth color gradients; daisy-chain 10+ ICs for 160+ LED control from one MCU
• RGB Signage: Dot correction EEPROM compensates for LED bin variations, ensuring uniform brightness across large displays
• Art Lighting: 120mA per channel drives high-power LEDs directly; external R_IREF adjusts global brightness
• Fault Monitoring: LOD detects broken LEDs; XERR can be OR-ed across all ICs to a single MCU interrupt pin
• Prototyping: PDIP-28 package plugs into breadboards for quick LED matrix development

TLC5940NT is a 16-channel PWM LED driver from TI in PDIP-28. The TLC5940RHR provides the same in QFN-32 for surface-mount. The TLC5947 provides 24-channel with 12-bit PWM in HTSSOP-28. The IS31FL3731 from ISSI offers 16×8 LED matrix driver in QFN-28. The MAX7219 from ADI/Maxim drives 8×7-segment displays with SPI. The HT16K33 from Holtek provides 16×8 LED matrix with I2C. The PCA9685 from NXP offers 16-channel 12-bit PWM for servos and LEDs in TSSOP-28.