LED driver for 4 parallel LEDs supports low voltage drop (<350mV) direct Li-ion applications for low vf LEDs Independent control loop for each LED Regulation, matching constant current in LEDs No external components No EMI and no switching noise Built-in DAC for digital and PWM brightness control Maximum efficiency up to 91% Up to 84ma (21ma/led) Bias current 2.7V to 5.5V input voltage range ICC<1µA 3mmx3mm MLP-8 package in shutdown mode.

application

Mobile phone handheld computer PDA, digital camera, MP3 player LCD display module keyboard backlight LED display.

illustrate

5610 -ic/" title="FAN5610 Product Specifications, Documentation and Sourcing Information" target="_blank">FAN5610 is for up to four LEDs, because each LED current source has its own automatic adjustment loop, accurate current matching even with Considerable forward voltage is spread among the LEDs. Therefore, LED preselection is not mandatory. To minimize voltage drop, and for efficiency, the value of the internal current sense resistor is very low (10Ω) in series with the LED .This is an important consideration for DC driving white LEDs in battery powered systems. The current of the LEDs can be set to 0mA (off mode), 7mA, 14mA and 21mA with a built in two bit digital to analog converter. Also Custom current settings can be used. When the control bits are set to zero, the internal circuitry is disabled and the quiescent current drops below 1 µA. Both digital inputs (A, B) are capable of pulse width modulation (PWM) .Using pwm, any average led current value can be obtained in the range of 1 to 20 mA. The fan 5610 is available in an 8-wire 3x3 mlp package.

application information

As shown in the block diagram, the FAN5610 includes four independent current regulators capable of maintaining a programmable constant current through the LEDs regardless of their forward voltage. This is correct over a wide range of voltages starting at +0.35V VF max, where VF max is the highest forward voltage fan 5610 driving the LEDs. The independence of the currents (LED current VIN and ventricular fibrillation changes less than 1% vin > vf (max) + 0.35v, as shown below.

By applying a continuous voltage level or pulse-width modulated signal at the built-in input of a digital-to-analog converter (DAC). When a PWM signal is used to drive the DAC input, current flows through the LED through the PWM signal to switch the frequency between two levels. Therefore, the average current varies with the duty cycle. The LED current waveform tracks the pwm signal, so the brightness of the LED depends on the duty cycle. For white LEDs, the spectral components are at the current level specified by the manufacturer. The DAC input should be programmed with the required current for white LED spectrum and pulse width modulation for dimming. To maintain the "purest" white color, the current through the LED should switch between zero and a specified current level (usually around 20 mA) corresponding to the white light chromaticity coordinates. Conversion errors are minimized, and the best LEDs to LEDs achieve matched settings over the entire range of average current, LED current between zero and maximum (A=1, B=1) when modulated using PWM brightness control.

Application example:

Example 1: Directly driving a low VF white or blue LED from a single cell Li-Ion When using a white or blue low VF LED, using a low voltage drop on the driver's side, VIN only needs 3.45V full 20mA LED current. Typically 5mA is available for the LED at 3.1V. Single-cell Li-ion is used in most applications, such as cell phones or digital cameras. In most cases, the voltage level of the Li-Ion battery drops to the 3.0V voltage level, not to the discharge level (2.7V) required before the charger is fully charged.

– voltage drop ~0.35V – VF (20mAh) < 3.1V (low VF) – VIN (20mAh) = vdrop+vf = 3.45V – VIN (typical 5mAh) ~ 3.1 volts where vin = single cell Li-Ion voltage Main advantages: No boost circuit required for LCD or keyboard Backlight directly connected to Li-Ion battery driver No EMI, no switching noise, no boost efficiency loss, no capacitors, no induction device. Example 2: An existing bus high VF white or blue LED from 4.0V to 5.5V has a forward voltage drop ranging from 3.3V to 4.0V. Driving these LEDs with a maximum current of 20mA for maximum brightness usually requires a single-cell Li-Ion voltage range boost circuit. In some cases, there is already a voltage bus in the system that can be utilized. Because of the FAN5610, the VIN only needs to drop ~0.35V from the LED connected to the FAN5610 VF (at 20mA) = 3.3V to 4.0V (VFVdrop + VF = 4.35V (max) where vin = existing bus = 5v

Main advantage: No boost circuit required for LCD or keypad backlighting. Drivers utilize existing bus low voltage drop at the lowest possible voltage level.