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| ACE714 Technology Description High Efficiency Low Noise PFM Step-up DC/DC Converter The ACE714 PFM step-up Converter drives white LEDs with a constant current to provide backlight in cell phones, PDAs, and other handheld devices. It features allowing series connection of the white LEDs so that the LED currents are identical for uniform brightness. An enable input can be pulsed repeatedly to adjust LEDs brightness. The fast 500HKz to 2MHz operation frequency allows for smaller capacitor and inductor. Fault condition protection uses cycle-by cycle current limiting to sense maximum inductor current and over-voltage protection. The 0.2V low reference voltage minimized the power loss across the current sense resistor. The converter can operate from 2V to 6V, and capable of delivering maximum 200mA output current at 4-LEDs application with 3V input voltage is as low as 120uA. All of these features make ACE714 be suitable for the portable devices, which are supplied by a single battery. ACE714 is available in SOT-23-6 package that is PB free. * * * * * * * * * * * * Features Up to 24V Output Voltage Wide Operation Range: 2V to 6V Maximum 2MHz Operating Frequency PWM Dimming Control Shutdown Current <1uA Current Limit Cycle-by-Cycle Low Current Sense Threshold: 200mV 24V Over Output Voltage Protection Compact SOT-23-6 Package Application Compact Back Light Module Power Source for LED Constant Current Source VER 1.2 1 ACE714 Technology Typical Application L1 Vin 10uH D1 SS14 High Efficiency Low Noise PFM Step-up DC/DC Converter LED 1 LED 17 LED2 + Cin 4.7uF + Cout 4.7uF LED 18 LED 3 LED 19 ON OFF Vin LX ACE714 OVP CE FB GND ACE714 LED 4 R1 LED 20 R5 Figure 1. ACE714 Typical Application Circuit Absolute Maximum Ratings Parameter Input voltage CE Pin Voltage Lx Pin Output Current Lx Pin Voltage Operating Junction Temperature (TJ) Ambient Temperature (TA) Power Dissipation SOT-23-6 Storage Temperature (Ts) Max -0.3 to 8 -0.3 to (Vin+0.3V) 1.6A 24V 125 -40 to 85 250mW -40 to 150 Packaging Type SOT-23-6 6 5 4 1 2 3 Pin SOT-23-6 Function LX 1 Switching Pin GND 2 Ground Pin FB 3 Pin for Feedback Voltage CE 4 Chip Enable Pin (Active with "H") OVP 5 Over Voltage Protection VIN 6 Power Supply Pin VER 1.2 2 ACE714 Technology Ordering Information Selection Guide ACE714 XX + H Halogen - free Pb - free GM : SOT-23-6 High Efficiency Low Noise PFM Step-up DC/DC Converter Block Diagram Electrical Characteristics (TA=25, Vin=3V, VCE=3V, unless otherwise noted) Parameter Operating Input Voltage Feedback Voltage FB Pin Bias Current Quiescent Current Maximum switching Frequency Switching Current Limit Switch VCESAT Switching pin Leak Current CE Voltage High CE Voltage Low CE Pin Bias Current Over Voltage Protection Symbol Vin VFB IFB IQ FOSC_MAX ILimit VCESAT ILX VCEH VCEL ICE VOVP Conditions Min 2 0.19 10 Typ 0.20 45 93 0.4 2 1.6 260 0.11 0.65 0.61 18 24 VFB=0.3V VCE=0V VFB=0V ILX=300mA VLX=5V VCE=0 to 3V VCE=3 to 0V Max 6 0.21 100 120 1.0 Units V V nA uA uA MHz A mV uA V V uA V VER 1.2 3 ACE714 Technology Typical Performance Characteristics High Efficiency Low Noise PFM Step-up DC/DC Converter VER 1.2 4 ACE714 Technology High Efficiency Low Noise PFM Step-up DC/DC Converter Application Information Dimming Control 1. Using a PWM Signal to CE Pin When adding the PWM signal to CE pin, the ACE714 is turned on or off by the PWM signal, so the LEDs operate at either zero or full current. The average LED current increase proportionally with the duty cycle of the PWM signal. The frequency range of the PWM signal is from 1 kHz to 300KHz. 2. Using a DC Voltage From the Figure 2, we can add a DC voltage to FB pin, we adjust the LED current by changing the DC voltage, which control the brightness, DC voltage range is from 0V to 2V. VER 1.2 5 ACE714 Technology High Efficiency Low Noise PFM Step-up DC/DC Converter ACE714 Figure 2. Dimming Control Using a DV Voltage 3. Using a Filtered PWM Signal The filtered PWM signal can be considered as an adjustable DC voltage. It can be used to replace the variable DC voltage source in dimming control. The circuit is shown in Figure 3. ACE714 Figure 3. Dimming Control Using a Filtered PWM Signal VER 1.2 6 ACE714 Technology Packing Information SOT-23-6 High Efficiency Low Noise PFM Step-up DC/DC Converter VER 1.2 7 ACE714 Technology High Efficiency Low Noise PFM Step-up DC/DC Converter Notes ACE does not assume any responsibility for use as critical components in life support devices or systems without the express written approval of the president and general counsel of ACE Electronics Co., LTD. As sued herein: 1. Life support devices or systems are devices or systems which, (a) are intended for surgical implant into the body, or (b) support or sustain life, and shoes failure to perform when properly used in accordance with instructions for use provided in the labeling, can be reasonably expected to result in a significant injury to the user. 2. A critical component is any component of a life support device or system whose failure to perform can be reasonably expected to cause the failure of the life support device or system, or to affect its safety or effectiveness. ACE Technology Co., LTD. http://www.ace-ele.com/ VER 1.2 8 |
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