EC4304B E-CMOS | Alldatasheet

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Technical content

PWM Control 1.2A Step-Down Converter EC4304B E-CMOS Corp. (www.ecmos.com.tw) Page 1 of 11 2011/10/06

FEATURES

  • Wide Input Voltage Range: 7V to 36V
  • LED Output Current Up to 1.2A
  • Soft-start
  • Single pin on/off and brightness control using DC voltage or PWM
  • High efficiency (up to 97%)
  • Up to 1MHz switching frequency
  • Typical 5% output current accuracy
  • SOT-23, SOT-89 Lead-free Package .

Applications

  • LED/Display Back Light Driver
  • Lightings
  • Portable Communication Devices
  • Handheld Electronics PART NUMBER EXAMPLES PART NO. PACKAGE EC4304BNB2R SOT-23-5 EC4304BNB6R SOT-89-5 GENERAL DESCRIPTION The EC4304B is a continuous mode inductive step-down converter, designed for driving single or multiple series connected LEDs efficiently from a voltage source higher than the LED voltage. The device operates from an input supply between 7V and 36V and provides an externally adjustable output current of up to 1.2A. Depending upon supply voltage and external components, this can provide up to 42 watts of output power. The EC4304B includes the output switch and a high- side output current sensing circuit, which uses an external resistor to set the nominal average output current. Output current can be adjusted above, or below the set value, by applying an external control signal to the 'ADJ' pin. The ADJ pin will accept either a DC voltage or a PWM waveform. Depending upon the control frequency, this will provide either a continuous or a gated output current. The PWM filter components are contained within the chip. The EC4304B is available in SOT-23, SOT-89 Lead-free package. PIN ARRANGEMENT(Top view) EC4304BNB2R EC4304BNB6R SOT-23-5 SOT-89-5

PWM Control 1.2A Step-Down Converter EC4304B E-CMOS Corp. (www.ecmos.com.tw) Page 2 of 11 2011/10/06 PIN DESCRIPTION SYMBO L SOT-23 SOT-89 DESCRIPTION LX 1 1 Drain of NDMOS switch GND 2 2 Ground ADJ 3 3 Multi-function On/Off and brightness control pin:

  • Leave floating for normal operation.(VADJ = VREF = 1.25V giving nominal average output current IOUTnom = 0.1/RS)
  • Drive with DC voltage (0V < VADJ < 2.5V) to adjust output current from 0% to 200% of IOUTnom
  • Drive with PWM signal from open-collector or open-drain transistor, to adjust output current. Adjustment range 0% to 100% of IOUTnom for f >10kHz and 0% to 100% of IOUTnom for f < 500Hz ISENS E 4 4 Connect resistor RS from this pin to VIN to define nominal average output current IOUTnom = 0.1/RS VIN 5 5 Input voltage (7V to 30V). Decouple to ground with 10uF or higher X7R ceramic capacitor close to device ABSOLUTE MAXIMUM RATINGS Parameter Symbol Value Unit Voltage on intput pin relative to GND VIN -0.3 to +36 V ISENSE pin Voltage -5 to +0.3 V ADJ and EN pin Voltage -0.3 to +6 V Operating Temperature Rang TA -40 to +125 C Maximum Soldering Temperature (at leads, 10 sec) TLEAD 300 C Storage Temperature Rang TS -65 to +150 C Power Dissipation, PD @ TA = 25°C SOT-23 0.35 WSOT-89 0.5 Package Thermal Resistance, θJA SOT-23 250 °C/WSOT-89 200

PWM Control 1.2A Step-Down Converter EC4304B E-CMOS Corp. (www.ecmos.com.tw) Page 3 of 11 2011/10/06 Electrical Characteristics (TA = -40 to 85°C unless otherwise noted. Typical values are at TA =25°C, VDD =12V) Symbol Description Conditions Min. Typ. Max Unit VIN Input Voltage 7 - 30 V VIRU Internal regulator start-up threshold VIN rising 5.65 V VIRD Internal regulator shutdown VIN falling 5.55 V IQOFF Quiescent supply current with output off EN pin grounded 35 uA IQON Quiescent supply current with output switching ADJ pin floating f = 250kHz 1.8 5.0 mA VSENSE Mean current sense threshold Voltage (Defines LED current setting accuracy) Measured on ISENSE pin with respect to VIN, VADJ = 1.25V 95 100 105 mV VSENTH Sense threshold hysteresis ±15 % ISENSE ISENSE pin input current VSENSE =VIN – 0.1 10 uA VREF Internal reference voltage Measured on ADJ pin with pin floating 1.25 V ∆VREF/∆T Temperature coefficient of VREF 50 ppm/K VADJ External control voltage range on ADJ pin for DC brightness control* 0 2.5 V VIHEN EN Input Voltage Hight 2 V VILEN EN Input Voltage Low 0.5 V RADJ Resistance between ADJ pin and VREF 0< VADJ < 2.5V 200 Kohm ILXM Continuous LX switch current 1.2 A RLX LX Switch ‘On’ resistance @ ILX = 1.2 A 0.3 0.45 ohm ILXI LX switch leakage current 5 uA TTP Thermal Shutdown Protect 160 C Electrical Characteristics (continuous) DPWML Duty cycle range of PWM signal applied to ADJ pin during low frequency PWM dimming mode PWM frequency<500Hz PWM amplitude = VREF Measured on ADJ pin 0.01 1 Brightness control range 100:1 DPWMH Duty cycle range of PWM signal applied to ADJ pin during high frequency PWM dimming mode PWM frequency>10KHz PWM amplitude = VREF Measured on ADJ pin 0.16 1 Brightness control range 5:1 fLX Operating frequency ADJ pin floating, L = 33uH (0.093 ohm) IOUT=1A @VLED = 3.6V Driving 1 LED 280 KHz TONmin Minimum switch ‘ON’ time LX switch ‘ON’ 240 ns TOFFmin Minimum switch ‘OFF’ time LX switch ‘OFF’ 200 ns TONminR Recommended minimum switch 'ON' time LX switch ‘ON’ 800 ns fLXmax Recommended maximum operating frequency 1 MHz DLX Recommended duty cycle range of output switch at fLXmax 0.3 0.7 TPD Internal comparator propagation delay 50 ns

PWM Control 1.2A Step-Down Converter EC4304B E-CMOS Corp. (www.ecmos.com.tw) Page 4 of 11 2011/10/06 Notes : *100% brightness corresponds to VADJ = VADJ(nom) = VREF. Driving the ADJ pin above VREF will increase the VSENSE. threshold and output current proportionally. **Parameters are not tested at production. Parameters are guaranteed by design, characterization and process control. Block Diagram V C C V IN R S D 1 L E D L 1 L X C 1 4 .7 u F V re f. M N R 1 B u ffe r R 4 A D J + D riv e r E N V o lta g e re g ula to r In te rn a l R 2 V D D B a n d g ap O v e r T e m p . R 3 G N D

PWM Control 1.2A Step-Down Converter EC4304B E-CMOS Corp. (www.ecmos.com.tw) Page 5 of 11 2011/10/06 Functional Description The device, in conjunction with the coil (L1) and current sense resistor (RS), forms a selfoscillating continuous-mode buck converter. Device operation Operation can be best understood by assuming that the ADJ pin of the device is unconnected and the voltage on this pin (VADJ) appears directly at the (+) input of the comparator. When input voltage VIN is first applied, the initial current in L1 and RS is zero and there is no output from the current sense circuit. Under this condition, the (-) input to the comparator is at ground and its output is high. This turns MN on and switches the LX pin low, causing current to flow from VIN to ground, via RS, L1 and the LED(s). The current rises at a rate determined by VIN and L1 to produce a voltage ramp (VSENSE) across RS. The supply referred voltage VSENSE is forced across internal resistor R1 by the current sense circuit and produces a proportional current in internal resistors R2 and R3. This produces a ground referred rising voltage at the (-) input of the comparator. When this reaches the threshold voltage (VADJ), the comparator output switches low and MN turns off. The comparator output also drives another NMOS switch, which bypasses internal resistor R3 to provide a controlled amount of hysteresis. The hysteresis is set by R3 to be nominally 15% of VADJ. When MN is off, the current in L1 continues to flow via D1 and the LED(s) back to VIN. The current decays at a rate determined by the LED(s) and diode forward voltages to produce a falling voltage at the input of the comparator. When this voltage returns to VADJ, the comparator output switches high again. This cycle of events repeats, with the comparator input ramping between limits of VADJ ± 15%. Switching thresholds With VADJ = VREF, the ratios of R1, R2 and R3 define an average VSENSE switching threshold of 100mV (measured on the ISENSE pin with respect to VIN). The average output current IOUTnom is then defined by this voltage and RS according to: IOUTnom = 100mV/RS Nominal ripple current is ±15mV/RS Adjusting output current The device contains a low pass filter between the ADJ pin and the threshold comparator and an internal current limiting resistor (200kohn nom) between ADJ and the internal reference voltage. This allows the ADJ pin to be overdriven with either DC or pulse signals to change the VSENSE switching threshold and adjust the output current. The filter is third order, comprising three sections, each with a cut-off frequency of nominally 4kHz. Details of the different modes of adjusting output current are given in the applications section. Output shutdown The output of the low pass filter drives the shutdown circuit. When the input voltage to this circuit falls below the threshold, the internal regulator and the output switch are turned off. The voltage reference remains powered during shutdown to provide the bias current for the shutdown circuit. Quiescent supply current during shutdown is nominally 35uA and switch leakage is below 5uA.

PWM Control 1.2A Step-Down Converter EC4304B E-CMOS Corp. (www.ecmos.com.tw) Page 6 of 11 2011/10/06 Applications Information Setting nominal average output current with external resistor RS The nominal average output current in the LED(s) is determined by the value of the external current sense resistor (RS) connected between VIN and ISENSE and is given by: IOUTnom = 0.1/RS [for RS ≥ 0.066 ohm] The table below gives values of nominal average output current for several preferred values of current setting resistor (RS) in the typical application circuit : RS (ohm) 0.066 0.1 0.142 0.285 Nominal average output current (mA) 1500 1000 700 350 The above values assume that the ADJ pin is floating and at a nominal voltage of VREF (=1.25V). Note that RS = 0.066ohm is the minimum allowed value of sense resistor under these conditions to maintain switch current below the specified maximum value. It is possible to use different values of RS if the ADJ pin is driven from an external voltage. (See next section) Output current adjustment by external DC control voltage The ADJ pin can be driven by an external dc voltage (VADJ), as shown, to adjust the output current to a value above or below the nominal average value defined by RS. ADJ + EC4304B DC GND GND The nominal average output current in this case is given by: IOUTdc = (VADJ /1.25) x (0.1V / RS), [for 0 < VADJ <2.5V] Note that 100% brightness setting corresponds to VADJ = VREF. When driving the ADJ pin above 1.25V, RS must be increased in proportion to prevent IOUTdc exceeding 1.5A maximum. The input impedance of the ADJ pin is 200kohm ±25%. Output current adjustment by PWM control Directly driving ADJ input A Pulse Width Modulated (PWM) signal with duty cycle DPWM can be applied to the ADJ pin, as shown below, to adjust the output current to a value above or below the nominal average value set by resistor RS: PWMVADJ A D J EC4304B G N D

PWM Control 1.2A Step-Down Converter EC4304B E-CMOS Corp. (www.ecmos.com.tw) Page 7 of 11 2011/10/06 Driving the ADJ input via open collector transistor The recommended method of driving the ADJ pin and controlling the amplitude of the PWM waveform is to use a small NPN switching transistor as shown below: PWM ADJ EC4304B GND This scheme uses the 200k resistor between the ADJ pin and the internal voltage reference as a pull-up resistor for the external transistor. Driving the ADJ input from a microcontroller Another possibility is to drive the device from the open drain output of a microcontroller. The diagram below shows one method of doing this: MCU ADJ EC4304B GND If the NMOS transistor within the microcontroller has high Drain / Source capacitance, this arrangement can inject a negative spike into ADJ input of the EC4304B and cause erratic operation but the addition of a Schottky clamp diode (cathode to ADJ) to ground and inclusion of a series resistor (10K) will prevent this. See the section on PWM dimming for more details of the various modes of control using high frequency and low frequency PWM signals. Shutdown mode Taking the EN pin to a voltage below 0.8V for more than approximately 100us, will turn off the output and supply current will fall to a low standby level of 35uA nominal.

PWM Control 1.2A Step-Down Converter EC4304B E-CMOS Corp. (www.ecmos.com.tw) Page 8 of 11 2011/10/06 Capacitor selection A low ESR capacitor should be used for input decoupling, as the ESR of this capacitor appears in series with the supply source impedance and lowers overall efficiency. This capacitor has to supply the relatively high peak current to the coil and smooth the current ripple on the input supply. A minimum value of 47uF is acceptable if the input source is close to the device, but higher values will improve performance at lower input voltages, especially when the source impedance is high. In order to avoid high frequency noise influence and improve circuit stability, it is recommended to shunt a value of 0.22uF Capacitor. The input capacitor should be placed as close as possible to the IC. For maximum stability over temperature and voltage, capacitors with X7R, X5R, or better dielectric are recommended. Capacitors with Y5V dielectric are not suitable for decoupling in this application and should not be used. Inductor selection Recommended inductor values for the EC4304B are in the range 33uH to 100uH. Higher values of inductance are recommended at higher supply voltages in order to minimize errors due to switching delays, which result in increased ripple and lower efficiency. Higher values of inductance also result in a smaller change in output current over the supply voltage range. The inductor should be mounted as close to the device as possible with low resistance connections to the LX and VIN pins. The chosen coil should have a saturation current higher than the peak output current and a continuous current rating above the required mean output current. The inductor value should be chosen to maintain operating duty cycle and switch 'on'/'off' times within the specified limits over the supply voltage and load current range. LX switch on time : ton = L∆I / (VIN – VLED - Iavg (RS+rL+RLX)) , note: tonmin > 240ns LX switch off time : toff = L∆I / (VLED + VD + Iavg (RS+rL)) , note: toffmin > 200ns Where: “L” is the coil inductance (H) “∆I” is the coil peak-peak ripple current (A) {Internally set to 0.3 x Iavg} “rL” is the coil resistance (ohm) “RS” is the current sense resistance “Iavg” is the required LED current (A) “VIN” is the supply voltage (V) “VLED” is the total LED forward voltage (V) “RLX” is the switch resistance (ohm) {=0.3 ohm nominal} “VD” is the diode forward voltage at the required load current (V)

PWM Control 1.2A Step-Down Converter EC4304B E-CMOS Corp. (www.ecmos.com.tw) Page 9 of 11 2011/10/06 TYPICAL APPLICATION CIRCUITS VIN 7V to 36V RS 0.1 ohm 47uF 0.22uF LED * C3 47uH 0.1uF * C4 1000PF VIN NC AD J EC4304 B GND ISENSE LX * note : When outputs the big current, the noise are big, this and the system environment and PCB layout have the influential, may defer to the actual need to increase the capacitor filtration noise.

PWM Control 1.2A Step-Down Converter EC4304B E-CMOS Corp. (www.ecmos.com.tw) Page 10 of 11 2011/10/06 PACKAGE DIMENSIONS SOT-23-5 B B 1 B 2 A 1 A C 1 C C 2 F I D H G E Symbol Dimension in mm Dimension in inch B1 1.90(BSC) 0.075(BSC) B2 0.95(BSC) 0.037(BSC) C2 0 0.075 0.150 0 0.003 0.06 D 0.40 0.015 G 0.60(REF) H 0~8° I 5~15° 5~15°

PWM Control 1.2A Step-Down Converter EC4304B E-CMOS Corp. (www.ecmos.com.tw) Page 11 of 11 2011/10/06 PACKAGE DIMENSIONS SOT-89 D POLISHED(2X) E H B1 1 2 3 L C 10'(2X) B A e Symbol Dimension in mm Dimension in inch Min. Max. Min. Max. A 1.40 1.60 0.055 0.063 B 0.44 0.56 0.017 0.022 B1 0.36 0.48 0.014 0.019 C 0.35 0.44 0.013 0.017 D 4.40 4.60 0.173 0.181 E 2.29 2.60 0.090 0.102 H 3.94 4.25 0.155 0.167 e 1.50 BSC 0.059 BSC e1 3.00 BSC 0.118 BSC L 0.89 1.2 0.035 0.047 *Note : The thermal pad on the IC’s bottom has to be mounted on the copper foil. To eliminate the noise influence, the thermal pad is suggested to be connected to GND on PCB. In addition, desired thermal conductivity will be improved, if a heat-conducting copper foil on PCB is soldered with thermal pad. The thermal pad enhances the power dissipation. As a result, a large amount of current can be sunk safely in one package.