FP6745C FITIPOWER | Alldatasheet

Document overview

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Technical content

Features

  • Wide Range for PWM Dimming, Ranging from 100Hz to 50kHz
  • High Efficiency: 87%
  • Drives Up to 10 WLEDs
  • Fast 1.3MHz Switching Frequency
  • Low 300mV Feedback Voltage
  • Over Voltage Protection
  • Low Profile SOT-23-6 Packages
  • RoHS Compliant

Applications

  • Cellular Phones
  • Digital Cameras
  • LCD Panel Backlights
  • GPS Receivers
  • PDAs, Handheld Computers TR: Tape / Reel Blank: Tube C: Green FP6745C□□□ Package Type S6: SOT-23-6

fitipower integrated technology lnc. Figure 2. Typical Application Circuit of FP6745C SW Switch Pin. Connect inductor/diode here. Minimize trace area at this node to reduce EMI. GND Ground Pin. Connect directly to local ground plane. FB Feedback Pin. Reference voltage is 300mV. Connect cathode of the lowest LED and resistor here.

  1. Enable: Logic high enables the device; logic low forces the device into shutdown mode.
  2. Analog dimming control: apply 0.7V to 1.4V DC voltage signal.
  3. Digital dimming control: apply external 100Hz to 50kHz PWM pulse signal with amplitude greater than 1.5V.

VIN Input Supply Pin. Must be locally bypassed.

fitipower integrated technology lnc. Figure 3. Block Diagram of FP6745C

  • Power Dissipation @TA=25ºC:
  • Package Thermal Resistance (θJA): Note 1：Stresses beyond those listed under “Absolute Maximum Ratings" may cause permanent damage to the device. Recommended Operating Conditions

4 FP6745C-0.1-SEP-2011 FP6745C 85T fitipower integrated technology lnc.

Electrical Characteristics

(VIN=VEN=5V, TA=+25ºC, unless otherwise noted) Parameter Symbol Conditions Min Typ Max Unit Operating Input Voltage VIN 2.8 5.5 V Operation Current ISD VEN=0V 4 8 μA IQ VFB=0.2V 430 550 μA Switching Frequency fSW 1.0 1.3 1.5 MHz Maximum Duty Cycle Duty VFB=0V 92 % Under Voltage Lockout VIN Under Voltage Lockout UVLO VIN Rising 2.25 2.45 V Under Voltage Lockout Hysteresis 92 mV Open Lamp Shutdown Threshold VOV VSW Rising 40 41 V Enable EN OFF Threshold VEN Falling 0.4 V EN ON Threshold VEN Rising 0.6 V Minimum EN Dimming Threshold VFB=0V 0.7 V Maximum EN Dimming Threshold VFB=300mV 1.4 V Feedback FB Voltage VFB VEN=1.5V 285 300 315 mV FB Input Bias Current IFB VFB=0.1V -300 nA Output Switch SW ON-Resistance (Note2) RON 0.5 Ω SW Current Limit (Note2) ILM 1.33 A Thermal Shutdown (Note2) TSD 150 °C Note 2：The specification is guaranteed by design, not production tested.

5 FP6745C-0.1-SEP-2011 FP6745C 85T fitipower integrated technology lnc. Applications Information Operation The FP6745C is designed in a current mode, fixed-frequency pulse -width modulation (PWM) step-up converter to drive up to 10 series -connected WLEDs. The FP6745C operates well with a variety of external components. See the following sections to optimize external components for a particular application. Inductor Selection For most applications, a 4.7μH to 1 5μH is recommended for general used. The inductor parameters, current rating, DCR and physical size, should be considered. The DCR of inductor affects the efficiency of the converter. The inductor with lowest DCR is chosen for highest efficiency. The saturation current rating of inductor must be greater than the switch peak current, typically 1.33A. These factors affect the efficiency, output load capability, output voltage ripple, and cost. The inductor selection depends on the switching frequency and current ripple by the following formula: OUT IN LSW IN V V1If VL Where fSW is the 1.3MHz switching frequency. ∆IL is the inductor ripple current. Capacitor Selection The ceramic capacitor is ideal for FP6745C application. X5R or X7R types are recommended because they hold their capacitance over wide voltage and temperature ranges than other Y5V or Z5U types. The input capacitor can reduced peak current and noise at power source. The output capacitor is typically selected based on the output voltage ripple requirements. For most applications, a 10 μF input capacitors with a 0.47 μF output capacitor are sufficie nt for general used. A higher or lower capacitance may be used depending on the acceptable noise level. LED Current Setting The LED current is specified by resistor from the FB pin to ground. In order to have accurate LED current, precision resistors are preferred (1% is recommended). The LED current can be programmed by: ILED=300mV / RFB Over Voltage Protection The FP6745C has an internal open-lamp protection circuit. In the cases of output open circuit, when the LEDs are disconnected from the circuit or the LEDs fail open circuit, t he over -voltage function monitors the output voltage through SW pin to protect the converter against. The LED strings open will cause N -MOS to switch with a maximum duty cycle and come out output over-voltage. This may cau se the SW voltage exceed its maximum rating then damage built -in N -MOS. In the state, the OVP protection circuitry will be triggered if output voltage exceeds 41V (typ.). The FP6745C will then stop switching and latch off. The FP6745C will automatically recover normal operation until EN input is recycled or the V IN is re-started. Dimming Control There are two different types of dimming control circuits. The LED current can be set by modulating the EN pin with a DC voltage or a PWM signal. (1) DC Voltage The dimming control us es a DC voltage ranging from 0.7V to 1.4V which results in regulating FB voltage from 0V to 300mV, respectively. (2) PWM Signal Changing the LED forward current not only changes the intensity of the LEDs, but al so changes the color. Controlling the intensity of the LEDs with a direct PWM signal allows dimming of the LEDs without changing the color. Dimming the LEDs via a PWM signal essentially involves turning the LED on and off. The LEDs operate at either zero or full current. The amplitude of the PWM signal should be higher than the minimum EN dimming voltage (typically 1.4V) . The LED average current increases proportionally with the duty cycle of the PWM signal. The recommended duty cycle range is from 5% to100%. The color of the LEDs remains unchanged since the LED current value is either zero or a constant value. The dimming frequency of the PWM signal can up to 50kHz and still retain well linearity. To avoid audio noise, dimming frequency greater than 20kHz is recommended.

6 FP6745C-0.1-SEP-2011 FP6745C 85T fitipower integrated technology lnc. Applications Information (Continued) Layout Consideration The proper PCB layout and component placement are critical for all switching regulators . The careful attention should be taken to the high -frequency, high current loops to prevent electromagnetic interference (EMI) problems. Here are some suggestions to the layout of FP6745C design. a. The input capacitor should be located as closed as possible to the VIN and GND pin. b. Minimize the distance of all traces connected to the SW node. The external components, C OUT, L1, and D1 should be placed as close to the device as possible with short and wide route to obtain optimum efficiency. c. Keep the noise-sensitive feedback circuitry away from the switching node. Place feedback resistor as close as possible to FB pin. d. The ground terminal of COUT must be located as closed as possible to GND pin. Place COUT next to Schottky diode. In Backlight application, the system engineers usually place the C OUT close to the LED connector. The far C OUT of the FP6745C may result in variable VFB. Add one more C OUT close to FP6745C is recommended.

7 FP6745C-0.1-SEP-2011 FP6745C 85T fitipower integrated technology lnc. Outline Information SYMBOLS UNIT DIMENSION IN MILLIMETER MIN MAX A 0.90 1.45 A1 0.00 0.15 A2 0.90 1.30 B 0.30 0.50 D 2.80 3.00 E 2.60 3.00 E1 1.50 1.70 e 0.90 1.00 e1 1.80 2.00 L 0.30 0.60 Note：Followed From JEDEC MO-178-C. Carrier dimensions Life Support Policy Fitipower’s products are not authorized for use as critical components in life support devices or other medical systems.