Implementing LED Driver Chips
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.
Figure 1. Application Circuit Example Using the Toshiba TB62701AN 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.
Figure 2. Block Diagram of the Toshiba TB62701AN LED Driver Chip
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.
Figure 3. Implementing the LED Driver Using a 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.