feature

Two independent channels drive up to six LEDs per channel Adaptive output voltage drive to maximize efficiency PFM mode of operation for boost circuit Efficiency up to 85% Up to 2 x 20mA outputs Two built-in DACs for independent (digital ) Brightness Control of two channels LED current with duty cycle modulation, 0 to 20mA digital, analog and PWM brightness control 2.7V to 5.5V Input voltage range 500kHz operating frequency Soft-start function Low shutdown current: Icc Minimal external components required for <1µA no-load protection Space saving 4x4mm 12-lead MLP package

application

Mobile phone handheld computer PDA, DSC, MP3 player keyboard backlight LED display

illustrate

The FAN5608 is an integrated Schottky diode LED driver which takes 2.7v to 5v input voltage from battery. Internal mos switches and external inductors provide the necessary load voltage. A proprietary internal compensation loop continuously monitors the minimum LED cathode voltages of both channels and adjusts the output voltage to the minimum value. The minimum Vout is determined by the selected channel. This adaptability allows the FAN5608 architecture to provide high efficiency. Up to 12 LEDs can be connected in series as long as the sum of the forward voltages does not exceed the maximum specification of 24 volts. Matching the number of serial LEDs per channel with equivalent voltages is not required; the FAN5608 provides the highest efficiency and regulation in the best current balancing configuration. The FAN5608 has two internal two-bit D/A converters that provide independent programmability for each output channel. In analog programming, the "B" pin must be connected to ground (logic "0"); the resistor must be connected between pin "A" and a fixed supply voltage. The output current can be programmed to any desired range of values within the specified range. The Fan5608DHMPX is available in a 4x4mm 12-lead MLP package. An external resistor setting turns the device on and off.

Circuit Description

When the VIN pin is powered up and the system is enabled, the bandgap reference acquires its nominal value voltage (1.2V) and the soft-start cycle begins. Once "power good" is reached (when 0.5mA is flowing through the LED), the soft-start cycle stops and the boost voltage is increased to generate the selected current through the input control pins (A1, A2, B1, B2). If CH1 is not selected, the CH1 output pin is high, its output measurement is approximately equal to vout, and its LED is off. The Fan 5608 provides tight adjustment of the output current channel for selected LEDs. An internal feedback loop determines that the LED string requires the highest output voltage to maintain the preset current. It also adjusts the boost regulator based on the CH1 and CH2 feedback voltages and the A1, A2, B1, B2 input settings. If the LED strings of the channels have different forward voltages. If one channel is used, the other channel should be connected to logic low by connecting the corresponding DAC input. If the external output capacitor vout is shorted to ground, the internal Schottky diode can be damaged, which should be avoided.

LED brightness control

Control inputs are A1 and B1 for CH1 and A2, and B2 for CH2. b1 and b2 are required low (ground) and high VIN control signals. In analog mode, A1 and A2 are connected to external stabilized voltage source inputs through external resistors and B1 and B2 to ground. The water flows through the resistor at about 1000 Ω. LED dimming can statically or dynamically control the CH1 and CH2 inputs. The CH1 and CH2 outputs are directly driven by the A1, B1 and A2, B2 inputs, respectively. Either channel can be configured as analog or digital. Inputs A1 and A2 are analog inputs that can be connected to an external regulated voltage source, calculated as: EQ1 where the current multiplier is based on the electrical specification sheet. Inputs b1 and b2 are digital inputs and can only be set via "0" (low) or "1" (high) external logic. Static analog control In analog mode, the B1 and B2 inputs should be connected to ground or "0" logic. A1 and A2 controls the LED current through an external resistor (R), as shown in Figure 4, or an external voltage (vext) input. The ILED value can be entered using the formula or EQ 2 where 1.2V

PWM control in digital dynamic mode In digital dynamic mode, if input A1 and/or A2 are externally driven open-drain outputs, the pull-up resistor should be less than 10KΩ to ensure less than 0.7V to exit; VA > (VIN – 0.7V), according to the high logic requirement level. The logic level high (VH) and logic level low (VL) PWM signals shall be: (VIN – 0.7V)

To drive two separate sets of LEDs for best efficiency, the fan 5608 should have a near forward voltage. This is when the same number and type of LED are connected serially in each channel. If the application requires the two channels to be unbalanced, an external resistor can be added in series with a shorter LED string to reduce the voltage difference between the two channels and enhance the performance. Maximum difference in connecting LEDs It is not recommended to connect more than three LEDs in series with CH1 and CH2. The specific layout suggests that the Fan 5608 has a Dual Die Attach Pad (DAP) package. One DAP is connected to GND and the other is guaranteed so that it does not have to provide any external connection to the DAPS. Low power dissipation from the inside, the 4x4mm mlp package enables no additional copper fields on the printed circuit board. when? Looking at the bottom of the dual DAP device package, two exposed metal islands are visible galvanically isolated. The two IND pins should be connected externally. Depending on the application noise sensitivity, battery and IC input.

To drive two separate sets of LEDs for best efficiency, the fan 5608 should have a near forward voltage. This is when the same number and type of LED are connected serially in each channel. If the application requires the two channels to be unbalanced, an external resistor can be added in series with a shorter LED string to reduce the voltage difference between the two channels and enhance the performance. Maximum difference in connecting LEDs It is not recommended to connect more than three LEDs in series with CH1 and CH2.