EC4501 E-CMOS | Alldatasheet
Document overview
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- PDF pages: 10
Technical content
Features
- Drives Up to 5 Series White LEDs from 3V
- Up to 87% Efficiency
- 1.25MHz Fixed Switching Frequency
- Low 104mV Feedback Voltage
- Open Load Shutdown
- PWM Dimming
- SOT23‐6 Packages
- RoHS compliant
Applications
- Cell Phones
- Handheld Computers and PDAs
- Digital Cameras
- Small LCD Displays
White LED Set-up Converter EC4501 Pin Assignments Pin Description Pin Number Pin Name Description 1 SW Power Switch Output. Connect the inductor and the blocking Schottky diode to SW .
2 GND Ground
3 FB Feedback input pin. The reference voltage at this pin is 104mV . Connect the cathode of the lowest LED to FB and a current sense resistor between FB and GND. 4 EN Enable pin. A high input at EN enables the device and a low input disables the devices. When not used, connect EN to the input source for automatic startup. 5 OV Over Voltage Input. OV measures the output voltage for open circuit protection. Connect OV to the output at the top of the LED string. 6 IN Input Supply Pin. Must be locally bypassed.
White LED Set-up Converter EC4501
Ordering Information
Function Block Diagram of EC4501 Part Number Package Marking Marking Information EC4501NNB3R SOT23-6 4501f 1. Starting with underlined 5, a bar is for production year 2012. The next bar is mark on top of 0 is for year 2013. The next bar is mark on bottom of 0 is for year 2014. The next bar is mark on top of 1 is year for 2015. The naming pattern continues with consecutive characters for later years. 2. f is the week of production. The big character of A~Z is for the week of 1~26, and small a~z is for the week of 27~52.
White LED Set-up Converter EC4501 Absolute Maximum Ratings Recommended Operating Conditions Symbol Parameter Rating Unit VIN Input Voltage -0.3～6 V VSW VIO Voltage at SW Pin -0.5～25 V All Other I/O Pins GND‐0.3 to VDD+0.3 V PDMAX Power Dissipation (Note 2) Internally Limited W PTR1 Thermal Resistance，SOT‐23‐6, ΘJA 220 ℃/W Tstg Storage Temperature -55 to 150 ℃ Tsolder Package Lead Soldering Temperature 260℃, 10s ESD Susceptibility (Note 3) 3 kV Symbol Parameter Range Unit VIN VIN Supply Voltage 3 to 5.5 V VSW Output Voltage VIN to 20 V TOPT Operating Temperature -40 to +85 ℃
White LED Set-up Converter EC4501
Electrical Characteristics
The following specifications apply for VIN= VEN =3.6V TA=25 oC, unless specified otherwise. Symbol Parameter Test Conditions EC4501 Unit Min. Typ. Max. VIN Input Voltage 3.0 5.5 V VFB FB Pin Voltage Driving 4xLED@20mA 94 104 114 mV Isw SW Pin leakage Current VEN =0, VSW =20V 1 µA Ioff Operating Current（Shutdown） 0.1 1 µA Isby Operating Current（Quiescent） VFB=0.5V 100 350 µA Fsw Switching Frequency 1.0 1.25 1.5 MHz Dmax Maximum Duty Cycle VFB=0V 85 90 % VEN_H EN Minimum High Level 1.5 V VEN_L EN Maximum Low Level 0.4 V RON SW On Resistance 1.4 Ω ILIMIT SW Current Limit 400 mA VOV Open Circuit Shutdown Threshold VOV Rising 20 V
White LED Set-up Converter EC4501 Typical Performance Characteristics Efficiency vs Number of LEDs Dimming Control using PWM signal to EN pin VFB VS T emperature Fequency VS T emperature
White LED Set-up Converter EC4501 Typical Application Circuit OPERATION DESCRIPTION The EC4501 uses a constant frequency, peak current mode boost regulator architecture to regulate the series string of white LEDs. The operation of the EC4501 can be understood by referring to the simplified block diagram shown above. At the start of each oscillator cycle, the control logic turns on the power switch M1. The signal at the non‐inverting input of the PWM comparator is proportional to the switch current, summed together with a portion of the oscillator ramp When this signal reaches the level set by the output of error amplifier, the PWM comparator resets the latch in the control logic and turns off the power switch. In this manner, error amplifier sets the correct peak current level to keep the LED current in regulation. If the feedback voltage starts to drop, the output of the error amplifier increases. This results in more current to flow through M1, hence increasing the power delivered to the output.
White LED Set-up Converter EC4501 Function Description Driving Capability Inductor Selections Capacitor Selection The small size of ceramic capacitors makes them ideal for EC4501 applications. X5R and X7R types are recommended because they retain their capacitance over wider voltage and temperature ranges than other types such as Y5V or Z5U. A 1μF input capacitor and a 0.22 μF output capacitor are sufficient for most EC4501 applications. Diodes Selection Schottky diodes, with their low forward voltage drop and fast reverse recovery, are the ideal choices for EC4501 applications. The forward voltage drop of a Schottky diode represents the conduction losses in the diode, while the diode capacitance (CT or CD) represents the switching losses. For diode selection, both forward voltage drop and diode capacitance need to be considered. Schottky diodes with higher current ratings usually have lower forward voltage drop and larger diode capacitance, which can cause significant switching losses at the 1.25MHz switching frequency of the EC4501. A Schottky diode rated at 100mA to 200mA is sufficient for most EC4501 applications. Some recommended Schottky diodes are listed in the following table: L LED Current Control The LED current is controlled by the feedback resistor. The feedback reference is 104mV. The LED current is 104mV/Rfb. In order to have accurate LED current, precision resistors are preferred (1% is recommended). The formula and table for RFB selection are shown below Open Circuit Protection Open circuit protection will shut off the EC4501 if the output voltage goes too high when the OV pin is tied to the output. In some cases an LED may fail, which will result in the feedback voltage always being zero. The EC4501 will then switch at its maximum duty cycle boosting the output voltage higher and higher. By connecting the OV pin to the top of the LED string the EC4501 checks this condition and if the output ever exceeds 20V, the EC4501 will shut down. The part will not switch again until the power is recycled. PARTNUMBER DCR（Ω） CURRENT RATING （mA） MANUFACTURER LQH3C220 0.71 250 MURATA CDRH3D16‐220 0.53 350 SUMIDA LB2012B220M 1.7 75 TAIYO YUDEN LEM2520‐220 5.5 125 TAIYO YUDEN EJPC220KF 4.0 160 PANASONIC ILED（mA） RFB Value（Ω） 5 20.8 10 10.4 15 6.93 20 5.1 PART NUMBER FORWARD CURRENT （mA） VOLTAGE DROP （V） DIODE CAPACITAN CE MANUFACTURER CMDSH‐3 100 0.58@100mA 7.0@10V Central CMDSH2‐3 200 0.49@200mA 15@10v Central BAT54 200 0.53@100mA 10@25v Zetex
White LED Set-up Converter EC4501 Function Description Dimming Control There are three different types of dimming control circuits: 1. Using a DC Voltage For some applications, the preferred method of brightness control is a variable DC voltage to adjust the LED current. The dimming control using a DC voltage is shown in Figure 3. As the DC voltage increases, the voltage drop on R2 increases and the voltage drop on R1 decreases. Thus, the LED current decreases. The selection of R2 and R3 will make the current from the variable DC source much smaller than the LED current and much larger than the FB pin bias current. 2. Using a PWM Signal to EN Pin With the PWM signal applied to the EN pin, the EC4501 is turned on or off by the PWM signal. The LEDs operate at either zero or full current. The average LED current increases proportionally with the duty cycle of the PWM signal. A 0% duty cycle corresponds to zero LED current. A 100% duty cycle corresponds to full current. The frequency range of the PWM signal should be up to 100KHz 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. B Board Layout Consideration As with all switching regulators, careful attention must be paid to the PCB board layout and component placement. To maximize efficiency, switch rise and fall times are made as short as possible. To prevent electromagnetic interference (EMI) problems, proper layout of the high frequency switching path is essential. The voltage signal of the SW pin has sharp rise and fall edges. Minimize the length and area of all traces connected to the SW pin and always use a ground plane under the switching regulator to minimize interplane coupling. In addition, the ground connection for the feedback resistor R1 should be tied directly to the GND pin and not shared with any other component, ensuring a clean, noise‐ free connection.
White LED Set-up Converter EC4501
Package Information
SOT236 Package Outline Dimensions