feature

1.5MHz Rotation Frequency Low Noise Output Voltage Adjustable Up to 1.5A Peak Switching Current Low Shutdown Current: <1µA Circulating Current Limit Feedback Pin Over Voltage Protection Fixed Frequency PWM Operation Soft Start Capability Internal Compensation Thermal Shutdown Good Load Adjustment: 0.2% low ripple 6 lead 3x3mm MLP

application

Portable Display Cell Phone/Smartphone LED Backlight Display Deviation PDA, DVD, Camera Backlight Pager and Cordless Phone Display Portable Medical Diagnostic Equipment Remote Control MP3 or PMP or DSC Player Serial Flash LED Driver

illustrate

The FAN5336 is a high efficiency, low noise, fixed frequency pulse width modulation, current mode, DC-DC boost regulator. It is designed for backlight supply applications for small LCD bias supply and white LEDs. Depending on the application, the FAN5336 regulator can deliver 50ma output current at voltages up to 33V. When the output voltage is up to 21V, the output current can reach 100mA. The FAN5336 can be used for power conversion down to 9V output voltage. The current mode control loop has fast transients providing good load regulation in response to 0.2% of the output voltage. The fan 5336 switch is at a fixed position 1.5MHz frequency, allowing the use of small, low-cost external components. Constant frequency switching results in low input noise and small output capacitance. The FAN5336 provides circulating current limit up to 1.5A peak current. Fan 5336 can be used to drive serial flash LEDs up to 100mA at 21V maximum on time for 400ms with 10% duty cycle. Low emi mode reduces interference and radiated electromagnetic energy caused by inductor ringing. Additional features include thermal shutdown, overvoltage protection, cycle-by-cycle current limit, low ripple, and soft-start support. The device is available in a 3x3mm 6-lead MLP packaged in 0.8mm thickness.

Circuit Description: The FAN5336 is a pulse width modulation (PWM) current mode boost converter. The FAN 5336 improves the performance of battery powered devices by significantly reducing the spectral distribution of noise input caused by the switching action of the regulator. To facilitate effective noise filtering, the switching frequency is chosen to be high, 1.5 MHz. Internal soft-start circuit minimizes inrush current. Timing selection soft-start circuit reaches nominal output voltage within 5ms after start-up Command cout (RMS) = 4.7μf when vin=2.7v, vout=21v, iload=35ma. The device architecture is an internal sense resistor in series with the current mode controller and the channel switch. The voltage at the feedback pin is the output voltage of the outer Schottky cathode of the diode (as shown in the test circuit). The error amplifier amplifies the difference between the feedback voltage and the internal bandgap reference. The amplified error voltage is used as a pulse width modulation comparator. The PWM's inverting input comparator consists of the sum of two parts: the amplified control signal received from the 30mΩ current sense resistor and the ramping generator voltage from the oscillator. The oscillator sets the latch and the latch turns on the FET switch. During normal operation, the PWM comparator resets the latch and turns off the FET, terminating the pulse. Since the comparator input contains information about the output voltage and the control loop is arranged as a negative feedback loop, the inductor current peak is adjusted to maintain regulation. Each time the latch resets, the FET turns off and the current through the switch is terminated. This latch can also be reset by other events, such as overcurrent and overvoltage conditions. The overcurrent condition is monitored by the current limit comparator, which resets the latch and closes the switching cycle within each clock. An overvoltage condition at the FEEDBACK (FB) pin is detected by a fast comparator that limits the duty cycle in a manner similar to overcurrent monitoring.

Application Information: Set the output voltage internal feedback voltage reference (VREF) to 1.23V (typ). The output voltage is divided by a resistor divider with R1 and R2 connected to the FB pin. The output voltage is calculated in units: The maximum output current depends on the output voltage setting. Table 1 provides suggested voltages for several steady-state configurations:

Inductor selection Inductor parameters that are directly related to device performance are saturation current and DC resistance. The typical inductance value for this FAN5336 is 6.8µh. The lower the DC resistance, the higher the efficiency. Balancing inductor size, cost, and overall efficiency allows for the best choice. The inductor saturation current should be rated at 1.5A, which is the threshold circuit for the internal current limit. Only at startup and under heavy load. When this happens, it results in higher ripple and reduced efficiency due to the automatic shutdown of the switching transistor. Capacitor Selection For optimum performance, low ESR input and output capacitors are required. Ceramic capacitors with CIN=10µF and cout=4.7µF as close as possible to IC pins are recommended for lower input and output ripple. The output capacitor voltage rating should be selected according to the Vout setting. Diode Selection External diodes for rectification are usually Schottky diodes.

Its average forward current should exceed the load current and its reverse voltage maximum rating should exceed the output voltage. converter. Barrier Schottky diode, such as BAT54 , because of its reverse current ratio over temperature range. Care should be taken to avoid shorting VOUT to ground, even if the IC is disabled, as the diode can be instantly damaged by excessive current. The Flash LED Driver Fan 5336 can be used to drive serial flash LEDs up to 100mA at 21V maximum on time for 400ms with a 10% duty cycle. Thermal Shutdown When the mold temperature exceeds 150°C, the reset occurs and remains active until the mold cools down to 130°C, when the circuit allows restarting. PCB Layout Recommendations The inherently high peak currents and switching frequencies of power supplies require careful PCB layout design. For best results, use wide trace paths at high currents and place input capacitors, inductors, and output capacitors as close to the IC circuit terminals as possible. The resistor divider voltage that sets the output should be kept away from the inductor to avoid RF coupling.

A four-layer printed circuit board with at least one ground plane connected to pin 2 of the IC is recommended. This ground plane acts as an electromagnetic shield to reduce electromagnetic interference and parasitic coupling between components.