TLC5947 — 24-Channel 12-Bit PWM Constant-Current LED Driver

Overview

The TLC5947 is a 24-channel constant-current sink LED driver IC manufactured by Texas Instruments. It features individually programmable 12-bit (4,096 step) PWM grayscale brightness control for each of its 24 outputs.

Widely featured on Adafruit 24-channel PWM LED breakout boards, the TLC5947 is designed for LED matrix displays, RGB LED mood lighting, backlighting, and servo control arrays. Operating from 3.0V to 5.5V DC, its open-drain constant-current outputs withstand up to 30V DC, allowing multiple series-connected LEDs per channel. Peak current across all channels is set globally using a single external resistor ( $R_{IREF}$ ).

Quick reference


Supply Voltage (`VCC`)	3.0 V to 5.5 V DC
Output Voltage Limit (`VOUT`)	Up to 30.0 V DC (Open-drain constant-current outputs)
LED Channels	24 Open-Drain Constant-Current Outputs (`OUT0` to `OUT23`)
PWM Grayscale Resolution	12-bit (4096 brightness levels per output channel)
Constant Current Range	$2.0\text{ mA}$ to $30.0\text{ mA}$ per channel (Set via $R_{IREF}$ )
Serial Interface Speed	Up to $30.0\text{ MHz}$ (`SCLK`)
Internal Oscillator	$4.0\text{ MHz}$ internal PWM clock oscillator
Package	32-pin HTSSOP (Pad Down) / 32-pin QFN

Pinout (HTSSOP-32 Package)

text

                       ┌─────────────┐
                 [GND] 1│ 1        32│ [VCC] (+3.0V to +5.5V)
                [BLANK] 2│            │31 [SOUT] (Daisy-Chain Out)
                 [SCLK] 3│            │30 [IREF] (Current Set Resistor)
                  [SIN] 4│  TLC5947   │29 [LAT] (Latch Pulse Input)
                 [OUT0] 5│  HTSSOP-32 │28 [OUT23]
                 [OUT1] 6│            │27 [OUT22]
                  ...   │            │...
                [OUT11] 16│            │17 [OUT12]
                       └─────────────┘

Pin	Name	Type	Description
1	`GND`	Power	Ground reference (0 V)
2	`BLANK`	Input	Blanking Control Input (High = Turn off all outputs; Low = Enable PWM)
3	`SCLK`	Input	Serial Data Clock Input
4	`SIN`	Input	Serial Data Input
5–16	`OUT0`–`OUT11`	Output	Channels 0 to 11 Constant-Current Sink Outputs
17–28	`OUT12`–`OUT23`	Output	Channels 12 to 23 Constant-Current Sink Outputs
29	`LAT`	Input	Latch Pulse Input (Rising edge transfers shift register data into PWM latches)
30	`IREF`	Input	Reference Current Setting Pin (Connect resistor $R_{IREF}$ to GND)
31	`SOUT`	Output	Serial Data Output for Daisy-Chaining (Connect to `SIN` of next TLC5947)
32	`VCC`	Power	Power Supply Input (+3.0V to +5.5V DC)

Output Current Formula

The maximum constant-current sink capability ( $I_{MAX}$ ) per channel is programmed via a single resistor $R_{IREF}$ connected between IREF (Pin 30) and GND:

$I_{MAX} = \frac{V_{IREF}}{R_{IREF}} \times 41.5 \approx \frac{1.20\text{V}}{R_{IREF}} \times 41.5 = \frac{49.8}{R_{IREF}} \text{ (Amps)}$

$\text{For } I_{MAX} = 20\text{ mA} \implies R_{IREF} \approx \frac{49.8}{0.020\text{A}} \approx 2.49\text{ k}\Omega.$

Common mistakes

Leaving BLANK (Pin 2) floating: BLANK disables all outputs when HIGH. If left floating, internal noise causes unexpected dimming or flashing. Connect BLANK to MCU GPIO or pull LOW to GND.
Exceeding package thermal dissipation limit: Operating 24 channels simultaneously at $30\text{ mA}$ with high voltage drop ( $V_{DS} > 3\text{V}$ ) generates significant heat ( $24 \times 0.03\text{A} \times 3\text{V} = 2.16\text{ W}$ ). Ensure the PowerPAD thermal pad is soldered to a large PCB ground plane.

Notes

TLC5947 vs PCA9685: TLC5947 has 24 channels, 12-bit PWM, and constant-current outputs (no series LED resistors needed); PCA9685 has 16 channels, 12-bit PWM, and voltage-driven open-drain outputs (requires external resistors).