feature

Three-Channel Parallel LED Driver for Wide Range of Forward Voltages Highest Diode Adaptive VOUT Regulation Forward Voltage Internally Matched LED Current Source Matched or Unmatched LED Current LED Built-in Charge Pump with Three Operating Modes: 1x, 1.5x and 2x efficiency up to 90 % PWM dimming frequency up to 50kHz Low EMI, low ripple Built-in 2-bit DAC to digitally control LED current

model

2.5V to 5.5V input voltage range Shutdown mode ICC<1µA 1MHz operating frequency Shutdown isolates output from input

application

Mobile PDA, DSC and MP3 Player

illustrate

The fan 5616 operates from a battery with an input voltage between 2.7 volts and 5.5 volts. The entire input voltage range is achieved using switch reconfiguration and divider switching techniques. The adaptable built-in charge pump eliminates the need for LED preselection (matching) and ensures high efficiency. The driver's built-in, proprietary, auto-sensing circuitry ensures the same high efficiency regardless of the number of LEDs. When the input voltage is sufficient - very high to maintain the programmed current level of the LEDs, the fan 5616 reconfigures itself to operate as a linear regulator and the charge pump is turned off. FAN5616 supports digital and pulse width modulation LED brightness control methods. The built-in 2-bit DAC provides selection of four LED current levels, each level being a percentage of the maximum LED current set externally. RSET resistor. Fan 5616 includes built-in shutdown, short circuit, and thermal protection circuits. A built-in smart soft-start circuit prevents excessive current draw at power-on while allowing increased dimming. Requires minimal external components. With only two 0.1µF to 1µF barrel capacitors, the 4.7µF input capacitor requires a 1µF output capacitor to function properly. The fan 5616 is packaged in a 3x3mm 16 lead MLP.

notes:

1. Stresses above those listed under "Absolute Maximum Ratings" may cause permanent damage to the device. This is a stress rating only, and the functional operation of the device under the above or any other conditions is not implied in the operating section of this specification. Extended exposure to absolute maximum rating conditions may affect device reliability. Absolute Maximum Ratings apply individually, not in combination. All other voltages are referenced to GND unless otherwise specified.

2. Junction-to-ambient thermal resistance θJA is a strong function of PCB material, board thickness, thickness as well as the number of vias used, the diameter of the vias used, the copper surface available, and additional heat sink characteristics. A reasonable estimate for zero airflow θJA at 0.5W is 60°C/W.

3. Using Mil Standard 883E, Method 3015.7 (Human Body Model) and EIA/Jesd222C101-A (Charging Device Model).

Circuit Description As shown, the switched capacitor DC/DC converter of the FAN5616 automatically configures its internal switches for high efficiency and provides tightly regulated output current to the LEDs. An analog detector determines which diode requires the highest voltage in order to maintain a preset current level, and adjusts the pump regulator accordingly. Each diode has its own linear current regulator. In addition, a voltage regulator can provide the maximum possible efficiency when the battery voltage is in the range of linear regulation. If the battery voltage is too low to maintain the diode current in linear mode, the fractional 3:2 charge pump is enabled. When the battery voltage drops and the mode is no longer sufficient for normal operation, the pump automatically reconfigures to operate in 2:1 mode. As the battery discharges the voltage drops and the fan 5616 maintains a constant current mode through the LEDs throughout the battery life. This transition has a hysteresis to prevent twisting. The device's internal supply voltage is automatically selected from the VIN or VOUT pins to have the higher voltage. The fan 5616 goes into shutdown mode to reduce the total DAC input current consumption (EN1 and EN2) is very low. Short Circuit and Thermal Protection If the output voltage is shorted, the output current will be limited to 65mA typical. Additionally, reset occurs when the mold temperature exceeds 150°C and remains effective until the mold cools down to 135°C. At this point the circuit will restart and resume normal operation.

Smart Soft Start When the FAN5616 is enabled, the Smart Soft Start circuit limits the inrush current of the switchgear. Figure 5 shows the timing diagram and associated signals of the smart soft-start circuit. After power up, the fan 5616 is in a low power state mode until a logic "high" is applied to the enable (EN1/EN2) pins to enable the device. When the device is enabled within the first 500 microseconds, the output voltage (VOUT) increases linearly until it reaches its nominal level. When a logic "low" is applied to EN1/EN2 for more than 5mS the device is in low power mode and the output voltage is turned off. The LED current is controlled by applying a pulse width modulated signal to the EN1/EN2 pins. To avoid the interference circuit between the PWM signal and the soft start, the applied PWM signal must be faster than 200Hz but not greater than 50kHz. A soft-start circuit will reactivate the EN1/EN2 pins on each low-to-high transition on . As shown in Figure 5, the PWM signal, ideally, should be controlled so that the initial logic "high" is at least 250 microseconds before returning to its standard frequency. This allows VOUT to rise to its nominal level. However, as shown, in most cases a PWM signal greater than 1kHz is applied to the EN1/EN2 pins, causing the VOUT ramp rate to slow down accordingly. The VOUT ramp will begin during the initial high point while its voltage will remain at its low level (off state). The following equations explain the duty cycle (D) and soft-start output ramp time (TSTR),

For example, a PWM signal with a 50% duty cycle (D=0.5) produces a 500 microsecond soft-start output ramp.

application information

LED Brightness Control Method 1. External RSET Resistor The external RSET resistor sets the maximum LED current for LED brightness control.

The resistor value determines the reference current requires a constant LED current. To calculate different RSET values, use the following formula:

2. Digital Control Built-in 2-bit DAC for digital control of LED brightness through EN1 and EN2 inputs Once the desired maximum LED current is set by an external RSET resistor, as described in Table 2, select a percentage of the maximum LED current to perform dimming operate

3. Control added to digital LED brightness control features of PWM controller According to the width of the PWM signal, the current change EN1 / once the maximum desired current (ILED-MAX) is set by an external RSET resistor, the maximum value of this resistor is ILED-MAX. The operation depends on the configuration of the PWM signal with the 2-bit DAC inputs (EN1 and EN2) As described in table 2. For example, if RSET=7.8K=84886then iled-max=20MA; if EN1 and EN2 are together, a PWM signal is application, the LED current will vary between 0% and 100%. The maximum LED current is regulated to the duty cycle of the PWM signal. A PWM signal can be applied to each of these inputs or both. Depending on the configuration, the average LED current can be Adjusted within any range limited by 0, 1/3, 2/3, 3/3 of the maximum LED current described in Table 3. The tea PWM duty cycle is assumed to be between 10% and 10%. 90%

The recommended PWM frequency range is 200Hz to an acceptable linear response of 50kHz. At higher position frequencies, the current waveform no longer follows the pulse width modulated signal waveform, resulting in an average ILED value with theoretical calculations.

4. DC voltage dimming Brightness control using variable DC voltage is as shown. If R1=78kΩ and R2=7.8kΩ, adjusting VEXT in the range of 0V to 0.6V results in LED dimming current from 22mA to 2mA.

The internal circuit of the fan 5616 maintains a constant VSET=0.6V. Adjusting VEXT will change ISET and ILED accordingly. By choosing different values for R1, R2 and VEXT, the ILED variation range can be changed according to the following formula:

Choosing a Capacitor It is important to choose the proper capacitor type and value to use for the FAN5616. To reduce battery ripple, lower capacitors should be used for both CIN and COUT. If necessary, the ripple can further power the fan 5616 filter through the RC input as shown.

Two 0.1µF to 1µF MLCC barrel capacitors are used for best efficiency in boost mode. For better I prescribe a 1µF barrel capacitor is recommended, especially when the current is >25mA and the battery is discharged below 3V. PCB Layout Considerations For best performance, it is recommended to use a solid ground plane on the backside of the printed circuit board. All capacitors should be connected as close as possible to the fan 5616 with fairly thick traces for ESL and ESR parasitics.