Discrete LED driver chips are common on many system boards. Supported Altera devices offer unique capabilities that allow you to integrate single or multiple LED driver chips into a single device.
Many LEDs, such as the seven-segment display, are common-anode LEDs. The LEDs anode connects to VCC and each cathode connects to an output pin of the current-sinking LED driver chip. The driver chip sinks the DC current required to drive the display, and the LED turns on when the driver chip's output pins drive low. Current-regulating circuits are implemented inside the LED driver chips.
Current-sinking LED drivers are more common than current-sourcing drivers.
|LED Driver Chip||Description|
|TLC5905||LED driver with shift registers, data latch, and constant current circuitry|
|TLC5910||LED driver with shift registers, data latch, on-chip phase-locked loop (PLL) for gray scale generation and constant current|
|TLC5911||LED driver with shift registers, data latch, on-chip PLL for gray scale generation and constant current|
|TLC5921||LED driver with shift register, data latch, and current-sink constant current circuitry|
|DS8874||9-digit shift input LED driver|
|DS8863||MOS-to-LED 8-digit driver|
|DS8963||MOS-to-LED 8-digit driver|
|TB62701AN||16-bit constant current LED driver with shift register and latch functions|
|TB62705||8-bit constant current LED driver with shift register and latch functions|
|TB62706||16-bit constant current LED driver with shift register and latch functions|
|TB62707||8-bit constant current LED driver with latch functions|
When using a supported Altera device as an LED driver chip, place a current-limiting resistor between the cathode side of the LEDs diode and the supported Altera device I/O. The LEDs anode is tied to VCC , and is turned on when the device I/O drive low.
The most important aspect of an LED driver chip is the amount of current it has to sink. Many LED applications call for a current sink specification of 5 to 15 mA. Because the supported Altera devices can sink up to 50 mA per pin, these devices can directly integrate commercial current-sinking LED driver chips.
|Device||Maximum Sink Current Per Pin (mA)|
|MAX II||25 1|
|MAX V||25 1|
|MAX 10||25 1|
Although a single pin from a MAX 7000B device can sink up to 50 mA of DC current, each GNDIO group can concurrently sink up to 200 mA of current due to the support of advanced I/O standards.
|Device||Maximum Source Current Per VCCIO Group (mA)||Maximum Sink Current Per GNDIO Group (mA)|
For example, the EPM240 device has six GNDIO pads, which provide six I/O regions that can sink up to 130 mΑ. If you need to sink 15 mA for the outputs, you can have eight outputs per region. With the six regions of I/O between GNDIO pads, there are 48 possible outputs, each sinking 15 mA.
The following figure shows an example of an application circuit with the Toshiba TB62701AN LED, its 16-bit constant current LED driver with shift registers and latch functions. The 16 outputs of the circuit sink current for two seven-segment displays. You can implement the LED driver chip in the circuitry using only one of the supported Altera device, provided the device has enough register and pin capabilities to replace the functionality of the entire LED driver chip.
The following figure shows a block diagram of the Toshiba TB62701AN LED driver chip. The Altera LED driver reference design has the same architecture as the TB62701AN. It consists of three main categories:
- 16-bit serial shift registers
- 16-bit latches
- An array of AND gates
The data from serial-in that determines which LED to be driven is shifted serially into the 16-bit shift registers for every low-to-high transition on the clock signal. With a high-to-low transition on the latch signal, the 16-bit data, which stores the 16-bit shift registers, is latched into 16-bit latches to drive the LED when the enable signals drive low.
The Altera LED driver reference design only emulates the functioning of the Toshiba TB62701AN. To implement the external resistor (R-EXT) and the current-regulating circuit, place an individual current-limiting resistor between the cathode side of the LEDs diodes and the I/O pins of the supported Altera device.
The right hand side of the figure above shows the connection between discrete LEDs and the I/O pins of a supported Altera device, while the left hand side shows the connection between a seven-segment LED and the supported Altera device. The output pins of the supported Altera device connected to the LEDs are driven low to turn on the LEDs.
The detailed description of the implementation is based on the MAX 10, MAX II, and MAX 3000A devices. This application can also be implemented in MAX V, MAX 7000A, MAX 7000B, and MAX 7000S devices.
You can target the LED drivers reference design in MAX 10 (10M08SAE144C8G), MAX II (EPM240T100C3), or MAX 3000A (EPM3064ATC44) devices using the Quartus® Prime software.
You can achieve design verification for the LED driver by using the Quartus Prime software. MAX II and MAX 3000A design verification occurs in both functional and timing simulations.
The LED driver is first configured so that the parallel_out drives an output value of 1010101010101010. In the final configuration, the parallel_out output value is 1111111100000000.
|September 2014||2014.09.22||Added MAX V and MAX 10 devices.|
|October 2008||2.3||Added note to Table 2.|