BCT3692BEYT-TR

BCT3692B High Efficiency, Support 0.3% PWM Dimming Boost WLED Driver BCT3692B High Efficiency, Support 0.3% PWM Dimming Boost WLED Driver GENERAL DESCRIPTION FEATURES The BCT3692B is a white LED driver with integrated boost converter. With an internal 38V switch FET, the BCT3692B drives up a string of up to 10 LEDs in series. The boost converter runs at 1.1MHz fixed switching frequency to reduce output ripple, improve conversion efficiency, and allows for the use of small external components.  Support 0.3% PWM dimming  1.1MHz Switching Frequency  38V Over-voltage Protection for up to 10 The default white LED current is set with the external sense resistor RSET, and the feedback voltage is regulated to 200mV, as shown in the typical application. During the operation, a pulse width modulation (PWM) signal can be applied to the CTRL pin through which the duty cycle determines the feedback reference voltage. BCT3692B integrates built-in soft-start function to minimize the power supply inrush current. BCT3692B also integrates over-current protection , LED open protection and over temperature protection(OTP) to prevent chip from entering abnormal operating conditions. LEDs in Series  200mV Reference Voltage  2.7V to 5.5V Input Voltage Range  Over-current and Over-temperature Protection  Built-in Soft-start Limits Inrush Current  Package Small TSOT23-6,SOT23-6 APPLICATIONS  Cellular Phones  Ultra Mobile Devices  Portable Media Players  PDAs, GPS Receivers  White LED Backlighting REV2.2 www.broadchip.com Copyright © BROADCHIP TECHNOLOGY CO., LTD 1 BCT3692B High Efficiency, Support 0.3% PWM Dimming Boost WLED Driver ORDERING INFORMATION Order Number Package Type Temperature Range Marking QTY/Reel BCT3692BEUT-TR TSOT23-6 -40°C to +85°C DDXX 3000 BCT3692BEYT-TR SOT23-6 -40°C to +85°C DGXX 3000 Note: "DD" in Marking is product short code for TSOT23-6 BCT3692B. "DG" in Marking is product short code for SOT23-6 BCT3692B. "XX" in Marking will be appeared as the batch code. PIN CONFIGURATION(Top View) TSOT23-6/SOT23-6 TOP VIEW 1 GND 2 FB 3 MARKING SW 6 VIN 5 NC 4 CTRL REV2.2 www.broadchip.com Copyright © BROADCHIP TECHNOLOGY CO., LTD 2 BCT3692B High Efficiency, Support 0.3% PWM Dimming Boost WLED Driver PIN DESCRIPTION NO. NAME I/O DESCRIPTION 1 SW I This is the switching node of the IC. Connect the inductor between the VIN and SW pin. This pin is also used to sense the output voltage for open LED protection. 2 GND G Ground. 3 FB I Feedback pin for current. Connect the sense resistor from FB to GND. 4 CTRL I Control pin of the boost regulator. It is a multi-functional pin which can be used for enable control and digital dimming. 5 NC - No Connect 6 VIN I The input supply pin for the IC. Connect VIN to a supply voltage between 2.7V and 5.5V. Typical Application Circuit REV2.2 www.broadchip.com Copyright © BROADCHIP TECHNOLOGY CO., LTD 3 BCT3692B High Efficiency, Support 0.3% PWM Dimming Boost WLED Driver ABSOLUTE MAXIMUM RATINGS(1) PARAMETERS RANGE Supply voltage range VIN(2) -0.3V to 6V Voltage on FB,CTRL (2) -0.3V to 6V Voltage on SW (2) -0.3V to 40V Junction-to-ambient thermal resistance θJA 255℃/W Operating free-air temperature range -40℃ to 85℃ Operating Junction temperature TJ -40℃ to 150℃ Storage temperature TSTG -65℃ to 150℃ Lead Temperature (Soldering 10 Seconds) 260℃ ESD ALL PINS HBM (human body model) ±2000V Latch-up +IT：450mA Latch-up current maximum rating per JEDEC standard -IT：-450mA (1) Conditions out of those ranges listed in "absolute maximum ratings" may cause permanent damages to the device. In spite of the limits above, functional operation conditions of the device should within the ranges listed in "recommended operating conditions". Exposure to absolute-maximum-rated conditions for prolonged periods may affect device reliability. (2) All voltage values are with respect to network ground terminal. RECOMMENDED OPERATING CONDITIONS Symbol Description MIN VIN Input voltage range, VIN (1) L Inductor CIN Input capacitor (1) TYP MAX UNIT 2.7 5.5 V 10 22 µH 1 10 µF 0.47 10 uF CO Output capacitor TA Operating ambient temperature -40 85 °C TJ Operating junction temperature -40 125 °C (1) These values are recommended values that have been successfully tested in several applications. Other values may be acceptable in other applications but should be fully tested by the user. REV2.2 www.broadchip.com Copyright © BROADCHIP TECHNOLOGY CO., LTD 4 BCT3692B High Efficiency, Support 0.3% PWM Dimming Boost WLED Driver ELECTRICAL CHARACTERISTICS Test Condition: TA = 25℃, VIN = 3.6V, VCTRL = VIN (Unless otherwise specified). PARAMETER TEST CONDITION MIN TYP MAX UNIT 5.5 V 2.39 V SUPPLY VOLTAGE AND CURRENT VIN Input voltage range 2.7 VUVLO Under-voltage lockout threshold VIN falling 2.2 Under-voltage lockout VHYS hysteresis 100 ISD Shutdown current VIN=4.2V 0.1 IQ Operating quiescent current VFB = 1V 250 mV VCTRL = GND, A 1 A PWM DIMMING CONTROL fPWM Frequency of PWM dimming 10 100 kHz DPWM PWM dimming duty cycle 0.3 100 % tMIN_ON Minimum on pulse width 50 ns VOLTAGE AND CURRENT CONTROL Voltage VREF feedback regulation 194 voltage Voltage feedback regulation VREF_PWM voltage 205 mV 2.25 mV 0.6 mV brightness PWM duty cycle = 0.3% control Voltage IFB under PWM duty cycle = 1% 200 feedback input bias current 0.1 1 A 0.4 0.7 Ω 0.7 Ω BOOST CONVERTER N-channel MOSFET VIN = 3.6V RDS(on) on-resistance VIN = 3.0V fS Oscillator frequency DMAX Maximum duty cycle 90 1100 kHz 93 % 1.5 A 38 V OCP AND OVP N-channel MOSFET current ILIM VOVP limit Open LED overvoltage Measured on the protection threshold SW pin REV2.2 www.broadchip.com Copyright © BROADCHIP TECHNOLOGY CO., LTD 5 BCT3692B High Efficiency, Support 0.3% PWM Dimming Boost WLED Driver CTRL INTERFACE VCTRL_H CTRL logic high voltage VIN = 2.7V to 5.5V VCTRL_L CTRL logic low voltage VIN = 2.7V to 5.5V RCTRL CTRL pull down resistor tOFF CTRL pulse width to shutdown 1.4 V 0.4 V kΩ 600 CTRL high to low 2.5 ms THERMAL SHUTDOWN TOTP Thermal shutdown threshold 165 ℃ 15 ℃ Thermal shutdown threshold THYS hysteresis REV2.2 www.broadchip.com Copyright © BROADCHIP TECHNOLOGY CO., LTD 6 BCT3692B High Efficiency, Support 0.3% PWM Dimming Boost WLED Driver Function Block Diagram REV2.2 www.broadchip.com Copyright © BROADCHIP TECHNOLOGY CO., LTD 7 BCT3692B High Efficiency, Support 0.3% PWM Dimming Boost WLED Driver DETAILED DESCRIPTION OPERATION The BCT3692B is a high efficiency, high output voltage boost converter in small package size. The device is ideal for driving up to 10 white LEDs in series. The serial LED connection provides even illumination by sourcing the same output current through all LEDs. The device integrates 38V/2A switch FET and operates in pulse width modulation (PWM) with 1.1MHz fixed switching frequency. The duty cycle of the converter is set by the error amplifier output and the current signal applied to the PWM control comparator. The control architecture is based on traditional current-mode control. Therefore, slope compensation is added to the current signal to allow stable operation for duty cycle larger than 50%. The feedback loop regulates the FB pin to a low reference voltage (200mV typical), reducing the power dissipation in the current sense resistor. SOFT START-UP Soft-start circuitry is integrated into the IC to avoid a high inrush current during start-up. After the device is enabled, the voltage at FB pin ramps up to the reference voltage. This ensures that the output voltage rises slowly to reduce the input current. OPEN LED PROTECTION Open LED over-voltage protection circuitry prevents IC damage as the result of white LED disconnection. The BCT3692B monitors the voltage at the SW pin during each switching cycle. The circuitry turns off the switch FET as soon as the SW voltage exceeds the VOVP threshold for 8 clock cycles. SHUTDOWN The CTRL input is used to enable or disable the BCT3692B. Pulling the CTRL pin higher than 1.4V will enable the device. The BCT3692B has an internal shutdown delay circuitry, when the CTRL pin is held low for an amount of time longer than 2.5ms, the BCT3692B will enter shutdown mode and the input supply current for the device is less than 1μA. Although the internal FET does not switch in shutdown, there is still a DC current path between the input and the LEDs through the inductor and Schottky diode. The minimum forward voltage of the LED array must exceed the maximum input voltage to ensure that the LEDs remain off in shutdown. However, in the typical application with two or more LEDs, the forward voltage is large enough to reverse bias the Schottky and keep leakage current low. UNDER-VOLTAGE LOCKOUT An under-voltage lockout prevents operation of the device at input voltage below typical 2.2V. When the input voltage is below the under-voltage threshold, the internal switch FET is turned off. If the input voltage rises by under-voltage lockout hysteresis, the IC restarts. CURRENT PROGRAM The loop of Boost structure will keep the FB pin voltage equal to the reference voltage VFB. Therefore, when Rset connects FB pin and GND, the current flows from VOUT through LED and Rset to GND will be decided by the current on Rset, which is equal to following equation: ILED = VFB / Rset REV2.2 www.broadchip.com Copyright © BROADCHIP TECHNOLOGY CO., LTD 8 BCT3692B High Efficiency, Support 0.3% PWM Dimming Boost WLED Driver Where ILED =output current of LEDs VFB =regulated voltage of FB Rset =current sense resistor PWM BRIGHTNESS DIMMING When the CTRL pin is constantly high, the FB voltage is regulated to 200mV typically. However, the CTRL pin allows a PWM signal to reduce this regulation voltage, it achieves LED brightness dimming. The relationship between the duty cycle and the FB voltage is given by the following equation: VFB = Duty x 200mV Where: Duty = duty cycle of the PWM signal 200mV = internal reference voltage The IC chops up the internal 200mV reference voltage at the duty cycle of the PWM signal. The pulse signal is then filtered by an internal low pass filter. The output of the filter is connected to the error amplifier as the reference voltage for the FB pin regulation. Therefore, although a PWM signal is used for brightness dimming, only the WLED DC current is modulated, which is often referred as analog dimming. This eliminates the audible noise which often occurs when the LED current is pulsed in replica of the frequency and duty cycle of PWM control. Unlike other scheme which filters the PWM signal for analog dimming, BCT3692B regulation voltage is independent of the PWM logic voltage level which often has large variations. THERMAL SHUTDOWN An internal thermal shutdown turns off the device when the typical junction temperature of is exceeded 165℃. The device is released from shutdown automatically when the junction temperature decreases by 15℃. REV2.2 www.broadchip.com Copyright © BROADCHIP TECHNOLOGY CO., LTD 9 BCT3692B High Efficiency, Support 0.3% PWM Dimming Boost WLED Driver APPLICATION INFORMATION MAXIMUM OUTPUT CURRENT The over-current limit in a boost converter limits the maximum input current and thus maximum input power for a given input voltage. Maximum output power is less than maximum input power due to power conversion losses. The current limit setting, input voltage, output voltage and efficiency can all change maximum current output. Therefore, the ripple has to be subtracted to derive maximum DC current. The ripple current is a function of switching frequency, inductor value and duty cycle. The following equations take into account of all the above factors for maximum output current calculation. 1 IP = 1 1 L × FS × ( + ) VOUT + VF − VIN VIN Where: IP = inductor peak to peak ripple L= inductor value VF = Schottky diode forward voltage FS = switching frequency VOUT = output voltage of the boost converter. It is equal to the sum of VFB and the voltage drop across LEDs. VIN × (ILIM − IP /2) × η IOUT_MAX = VOUT Where: IOUT_MAX = maximum output current of the boost converter ILIM = over-current limit, for worst case calculation the minimum value has to be chosen. η= efficiency INDUCTOR SELECTION Inductor value, saturation current, and Direct Current Resistance (DCR) are the most important parameters used to select an inductor for the BCT3692B. The suitable inductance range for this device is 10 μH to 22μH. Higher inductance lowers the value of the RMS current of the step-up converter. Together with a lower DCR value of the inductor, the total inductor power loss becomes much lower. Considering inductor size and cost, 10 μH inductance is recommended. The below table lists some recommended inductors for the BCT3692B. Recommend Inductors Part Number L(μH) DCR MAX Saturation Current (Ω) (mA) Size(L x W x H mm) Vendor LQH3NPN100NM0 10 0.3 750 3×3×1.5 Murata VLCF5020T-220MR75-1 22 0.4 750 5×5×2.0 TDK CDH3809/SLD 10 0.3 570 4×4×1.0 Sumida A997AS-220M 22 0.4 510 4×4×1.8 TOKO SCHOTTKY DIODE SELECTION The high switching frequency of the BCT3692B demands a high-speed rectification for optimum efficiency. Ensure that the diode average and peak current rating exceeds the average output current and peak inductor current. In addition, the REV2.2 www.broadchip.com Copyright © BROADCHIP TECHNOLOGY CO., LTD 10 BCT3692B High Efficiency, Support 0.3% PWM Dimming Boost WLED Driver diode’s reverse breakdown voltage must exceed the open LED protection voltage. To achieve better efficiency, a low VF Schottky diode is recommended. ONSemi MBR0540 and ZETEX ZHCS400 are recommended for the BCT3692B. OUTPUT CAPACITOR SELECTION The output capacitor is mainly selected to meet the requirements for the output ripple and loop stability. The output voltage of the BCT3692B could reach up to 38V. X7R type output capacitor rated of 50 V is suggested. To reduce power loss, a ceramic capacitor with a low Effective Series Resistance (ESR) is better. The capacitor in the range of 0.47uF to 10uF is recommended for input side. The recommended output capacitor value is 1uF. PCB LAYOUT CONSIDERATION For best performance of the BCT3692B, the following guidelines must be followed. 1. Input /Output capacitors should be placed close to the IC and connected to ground to reduce noise coupling.. 2. Keep the main current traces as possible as short and wide. 3. Vin will be connected with Vbattery with wide track, to avoid the interference of RF PA and Audio PA. REV2.2 www.broadchip.com Copyright © BROADCHIP TECHNOLOGY CO., LTD 11 BCT3692B High Efficiency, Support 0.3% PWM Dimming Boost WLED Driver PACKAGE INFORMATION TSOT23-6 Symbols A A1 A2 B B1 B2 C C1 C2 D θ Dimmensions in millimeters Min. Max. 2.82 3.02 0.95 (BSC) 0.35 0.50 1.60 1.70 2.65 2.95 0.08 0.20 0.70 0.80 0.00 0.10 0.38 0.44 0.30 0.60 。 9 TYP 。 θ1 θ2 10 TYP 0 。 8 。 REV2.2 www.broadchip.com Copyright © BROADCHIP TECHNOLOGY CO., LTD 12 BCT3692B High Efficiency, Support 0.3% PWM Dimming Boost WLED Driver SOT23-6 Symbols A A1 A2 b c D E1 E e e1 L L1 θ2 Dimmensions in millimeters Min. Max. 1.05 1.25 0.00 0.10 1.05 1.15 0.30 0.50 0.10 0.20 2.82 3.02 1.50 1.70 2.65 2.95 0.95 1.80 2.00 0.30 0.60 0.60 TYP 0 。 8 。 REV2.2 www.broadchip.com Copyright © BROADCHIP TECHNOLOGY CO., LTD 13 BCT3692B High Efficiency, Support 0.3% PWM Dimming Boost WLED Driver PCB Layout Pattern: TSOT23-6/SOT23-6 0.95 2.8 1.0 0.5 RECOMMENDED PCB LAYOUT PATTERN (Unit: mm) REV2.2 www.broadchip.com Copyright © BROADCHIP TECHNOLOGY CO., LTD 14