LED driver circuit
CAT3603 is a three channel charge pump LED driver IC from Catalyst Semiconductors that can be operated in either LDO mode or fractional mode. The IC can deliver 30mA per channel and can be operated from an input voltage range of 3 to 5.5V DC. CAT3063 has a quiescent current as low as 0.1uA and this makes it suitable for battery powered applications. The operating frequency is 1Mhz which makes it possible to use small capacitors. Another features are soft start, current limiting, high efficiency (90%) and short circuit protection. Applications of this IC are hand held devices, LCD back lights , LED lighting gadgets etc. The output current can be programmed using an external resistor connected between the RSET (pin 4) and ground.
Charge pump: Charge pump is a DC to DC converter circuit that uses capacitors as the energy storage component for creating an output voltage that is either higher or lower than the input voltage. A switching circuit (using BJTs or MOSFETs) is used for connecting and disconnecting the voltages from the storage capacitor. The switching frequency is usually in the kilo or MHz range. The output voltage will be a pulsed one and it is smoothed using an output filter capacitor. Charge pump circuits can double, triple, quadruple, multiply or scale any given voltage. In theory, a charge pump can generate any desired voltage.
CAT3063 LED driver circuit.
The circuit diagram of a three channel LED driver circuit using CAT3063 is shown below (Fig 1). C4 is an input filter capacitor. R1 is the resistor used for programming the output current. C3 is the output filter capacitor. C1 and C2 are the storage capacitors of the internal charge pump circuit. A logic high at pin 5 will enable the IC and a logic low on the same pin will drive the IC into shutdown mode. In the shutdown mode, the quiescent current is almost equal to zero. With the used value of R1, the LED current per channel will be 25mA.
When powered up the CAT6063 operates in 1X mode i.e, the output voltage will be equal to the input voltage. If this output voltage is enough to regulate the current through all LEDs, the IC remains 1X mode. If the output voltage is not sufficient enough to regulate the desired current through the LEDs, the device automatically switches to the 1.5X mode where the output voltage is 1.5 times the input voltage. This process is repeated when ever the IC is powered up or awaken from shutdown mode.
Selection of R1 is shown in the table below.
|LED current (mA)||R1 (kilo ohm)|
- CAT6063 is not suitable for resistive loads.
- Unused LED output channels must be connected to Vout pin. They cannot be left floating.
- All capacitors are ceramic capacitors.
- Dimming of the LEds can be achieved by using a DC voltage for setting the pin4 (RSET) current or by driving the pin5 (EN) using a PWM signal.
- There is an exposed pad beneath the IC and it should soldered to the ground plane of the PCB for improved thermal performance.
- Supply voltage should not exceed 6V DC.
- Total output current should not exceed 120mA.