BL9580 36V, 1.4A Step-down High Brightness LED Driver with Internal Switch FEATURES z z z z z z z z z z z z z z z z DESCRIPTION Simple low parts count Internal 36V NDMOS switch Up to 1.4A output current Single pin on/off and brightness control using DC voltage or PWM Soft Start High efficiency (up to 97%) Wide input voltage range: 6V to 36V Output shutdown Up to 1MHz switching frequency Inherent open-circuit LED protection Typical 3% output current accuracy High-side current sense Hysteretic control: no compensation Adjustable constant LED current Over temperature protection Pb-free SOT89-5 and SOP-8 packages APPLICATIONS z z z z z z Low voltage halogen replacement LEDs Automotive lighting Low voltage industrial lighting LED back-up lighting Illuminated signs LCD TV backlighting ORDERING INFORMATION The BL9580 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 6V and 36V and provides an externally output current up to 1.4A. Depending upon supply voltage and external components, this can provides up to 24 watts of output power. The BL9580 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 by applying an external control signal to the 'ADJ' pin. The ADJ pin will accept either a DC voltage or a PWM waveform. During DC dimming, this will provide a continuous output current that is proportional to the external applied DC voltage. During the PWM dimming, this will provide a gated output current and the average current is proportional to the duty cycle. Applying a voltage of 0.2V or lower to the ADJ pin turns the output off and switches the device into a low current standby state. TYPICAL APPLICATION BL9580 X XXX Rs Package: SRN: SOT89-5 SP8:SOP8 0.1ohm VIN(6V-36V) Features: P: Standard (default, lead free) C: Customized C1 4.7uF N/C GND PPMIC BU BL9580 Rev 1.7 5/2010 L1 D1 VIN ISENSE ADJ BL9580 LX GND www.belling.com.cn Belling Proprietary Information. Unauthorized Photocopy and Duplication Prohibited ©2010 Belling All Rights Reserved 47uH 1 BL9580 36V, 1.4A Step-down High Brightness LED Driver with Internal Switch Absolute Maximum Rating Input Supply Voltage (VIN) ISENSE Voltage (VISENSE) LX Output Voltage (VLX) Adjust Pin Input Voltage (VADJ) Switch Output Current (ILX) (Note 1) -0.3V to +40V +0.3V to -5V(Note2) -0.3V to +40V -0.3V to +6V 1.7A Maximum Junction Temperature 150°C Operating Temperature Range(Note3) -40°C to 125°C Storage Temperature Range -55°C to 150°C Lead Temperature (Soldering, 10s) 300°C Package Information SOT89-5 TOP VIEW ADJ 1 LX ISENSE 4 VIN MARKING GND 2 5 3 Part Number Top Mark BL9580(Note4) A YWW BL9580 Temp Range -40°C to +125°C Thermal Resistance (Note 5): Package SOT89-5 SOP-8 ӨJA 160°C/W 153°C/W ӨJC 45°C/W 39°C/W Note 1: Absolute Maximum Ratings are those values beyond which the life of a device may be impaired. Note 2: VISENSE measured respect to VIN。 Note 3: The BL9580 is guaranteed to meet performance specifications from 0°C to 70°C. Specifications over the –40°C to 125°C operating temperature range are assured by design, characterization and correlation with statistical process controls. Note 4: The first row printed BL9580, the second row printed A Y W W. Y: Year of wafer manufacturing W: Week of wafer manufacturing. Y Year WW Week 9 2009 A 2010 B 2011 C 2012 D 2013 01 1 … … 25 25 26 26 27 27 … … 51 51 52 52 Note 5: Thermal Resistance is specified with approximately 1 square of 1 oz copper. PPMIC BU BL9580 Rev 1.7 5/2010 www.belling.com.cn Belling Proprietary Information. Unauthorized Photocopy and Duplication Prohibited ©2010 Belling All Rights Reserved 2 BL9580 36V, 1.4A Step-down High Brightness LED Driver with Internal Switch Pin Description SOT89-5 3 2 PIN Note 6 SOP-8 7 6 NAME LX GND 1 5 ADJ 5 4 ISENSE 4 3 VIN 2 PGND FUNCTION Drain of NDMOS switch Ground (0V) Multi-function On/Off and brightness control pin: • Leave floating for normal operation. • Drive to voltage below 0.2V to turn off output current • Drive with DC voltage (0.3V < VADJ < 1.2V) to adjust output current from 25% to 100% of IOUTnom. If the ADJ voltage is larger than 1.2V, the output current is IOUTnom. • Drive with PWM signal from open-collector or open-drain transistor, to adjust output current. • Connect a capacitor from this pin to ground to activate softstart. (soft-start time is approx.0.06ms/nF) Connect resistor RS from this pin to VIN to define nominal average output current IOUTnom=0.1/RS Input voltage (6V to 36V). Decouple to ground with 4.7uF or higher X7R ceramic capacitor close to device Power ground. Note 6: PIN1, PIN8: NC(not connected) for SOP-8 package. Block Diagram V IN D1 L1 Rs V IN LX IS E N S E R1 C1 4 .7 u F OT P 5V V o lta g e R e g u la to r U VLO 1M oh m MN ADJ 1 .2 V Bandga p GND PPMIC BU BL9580 Rev 1.7 5/2010 R2 R 3 ADJ 0 .2 V www.belling.com.cn Belling Proprietary Information. Unauthorized Photocopy and Duplication Prohibited ©2010 Belling All Rights Reserved 3 BL9580 36V, 1.4A Step-down High Brightness LED Driver with Internal Switch Electrical Characteristics (Note 7) (Test conditions: VIN =12V, TA = 25°C, unless otherwise noted.) Symbol Parameter Conditions VIN Input voltage VUVLO Under voltage lock out VIN Rising VUVLO(HYS) IQ(OFF) IQ(ON) VISENSE UVLO hysteresis Quiescent supply current with output off Quiescent supply current with output switching Mean current sense threshold voltage VSENSE(HYS) Sense threshold hysteresis ISENSE VADJ IADJ ISENSE pin input current ADJ pin floating voltage ADJ pin leakage current ADJ pin pull up resistor to internal supply voltage DC voltage on ADJ pin to switch device from active (on) state to quiescent (off) state DC voltage on ADJ pin to switch device from quiescent (off) state to active (on) state Digital dimming ADJ pin input voltage high Digital dimming ADJ pin input voltage low DC brightness control Recommended Digital dimming frequency Duty cycle range of PWM signal applied to ADJ pin during low frequency PWM dimming mode Brightness control range Duty cycle range of PWM signal applied to ADJ pin during high frequency PWM dimming mode RADJ VADJ(OFF) VADJ(ON) VADJ(H) VADJ(L) VADJ(DC) fADJ DPWM(LF) DPWM(HF) 5.07 Unit V V VIN falling 4.87 V ADJ Pin grounded 50 100 μA 1.8 50 mA 100 103 mV ADJ Pin floating f=250KHz Measure on ISENSE pin with respect to VIN MIN 6 97 TYP MAX 36 ±15 VISENSE=VIN-0.1 ADJ pin floating ADJ pin grounded 1.2 5 5 % 10 1 μΑ V μΑ MΩ VADJ falling . 0.15 0.2 0.25 V VADJ rising 0.2 0.25 0.3 V 1.5 fADJ =100Hz V 0.2 V 0.3 1.2 V 0.1 20 kHz 0.1 100 % 100 % 1000:1 fADJ =10KHz 5 Brightness control range 20:1 RLX LX switch on resistance 0.35 0.7 Ω ILX(LEAK) LX switch leakage 0.1 5 μΑ PPMIC BU BL9580 Rev 1.7 5/2010 www.belling.com.cn Belling Proprietary Information. Unauthorized Photocopy and Duplication Prohibited ©2010 Belling All Rights Reserved 4 BL9580 36V, 1.4A Step-down High Brightness LED Driver with Internal Switch Electrical Characteristics (continued) (Test conditions: VIN =12V, TA = 25°C, unless otherwise noted.) Symbol Parameter Conditions ILX(MEAN) Continuous LX switch current TEN, DELAY Chip enable delay time TENB, DELAY Chip disable delay time fLX(MAX) TOTP TSD(HYS) Recommended maximum operating frequency Over temperature protection threshold Over temperature protection hysteresis The delay time between ADJ pin rising edge and LX pin falling edge The delay time between ADJ pin falling edge and LX pin rising edge MIN TYP MAX Unit 1.4 A 480 ns 25 ns 1 MHz Temperature rising 160 °C Temperature falling 20 °C Note 7: 100% production test at +25°C. Specifications over the temperature range are guaranteed by design and characterization. PPMIC BU BL9580 Rev 1.7 5/2010 www.belling.com.cn Belling Proprietary Information. Unauthorized Photocopy and Duplication Prohibited ©2010 Belling All Rights Reserved 5 BL9580 36V, 1.4A Step-down High Brightness LED Driver with Internal Switch Typical Performance Characteristics (Test conditions: VIN =12V, RS=0.1Ω, TA = 25°C, unless otherwise noted.) Efficiency Vs. Supply Voltage L=33uH 100 Deviation from nominal set current(%) Efficiency(%) 5 1LED 2LED 3LED 4LED 5LED 95 90 85 80 5 10 15 20 25 Output Current variation Vs. Supply Voltage L=33uH 4 2 1 0 -1 -2 -3 -4 -5 30 1LED 2LED 3LED 4LED 5LED 6LED 3 5 10 Supply Voltage VIN(V) Operating Frequency Vs. Input Voltage L=33uH 600 550 Freq(kHz) 400 350 70 250 200 60 50 1LED 2LED 3LED 4LED 5LED 6LED 40 30 150 20 100 10 50 5 10 15 20 25 0 30 5 10 Supply Voltage VIN(V) Deviation from nominal set current(%) Output Current(A) 1.03 1.02 1.01 1.00 0.99 0.98 0.97 0.96 0.95 5 25 30 1LED 2LED 3LED 4LED 5LED 6LED 4 3 2 1 0 -1 -2 -3 -4 5 10 15 20 25 30 -5 5 Supply Voltage VIN(V) PPMIC BU BL9580 Rev 1.7 5/2010 20 Output current variation Vs. Supply Voltage L=47uH 6 1LED 2LED 3LED 4LED 5LED 6LED 1.04 15 Supply Voltage VIN(V) Output Current Vs.Supply Voltage L=33uH 1.05 30 80 300 0 25 90 Duty Cycle(%) 450 20 Duty Cycle Vs. Input Voltage L=33uH 100 1LED 2LED 3LED 4LED 5LED 6LED 500 15 Supply Voltage VIN(V) 10 15 20 25 30 Supply Voltage VIN(V) www.belling.com.cn Belling Proprietary Information. Unauthorized Photocopy and Duplication Prohibited ©2010 Belling All Rights Reserved 6 BL9580 36V, 1.4A Step-down High Brightness LED Driver with Internal Switch Operating Frequency Vs. Supply Voltage L=47uH 600 550 90 400 350 80 70 Duty Cycle(%) 450 Freq(kHz) 100 1LED 2LED 3LED 4LED 5LED 6LED 500 Duty Cycle Vs. Supply Voltage L=47uH 300 250 200 60 50 40 1LED 2LED 3LED 4LED 5LED 6LED 30 150 20 100 10 50 5 10 1.08 20 25 1.04 1.02 10 5 15 20 25 4 2 1 0 -1 -2 -3 -4 -5 30 5 10 Operating Frequency Vs. Supply Voltage L=100uH Duty Cycle(%) Freq(kHz) 70 60 50 1LED 2LED 3LED 4LED 5LED 6LED 40 20 50 10 15 20 25 30 0 5 Supply Voltage VIN(V) PPMIC BU 5/2010 30 80 30 BL9580 Rev 1.7 25 90 100 10 20 Duty Cycle Vs.Supply Voltage L=100uH 100 1LED 2LED 3LED 4LED 5LED 6LED 5 15 Supply Voltage VIN(V) 150 0 30 1LED 2LED 3LED 4LED 5LED 6LED 3 Supply Voltage VIN(V) 200 25 Output Current variation Vs. Supply Voltage L=100uH 10 250 20 Output Current Vs. Supply Voltage L=47uH 0.96 300 15 Supply Voltage VIN(V) 0.98 5 5 Supply Voltage VIN(V) 1.00 0.94 0 30 1LED 2LED 3LED 4LED 5LED 6LED 1.06 Output Current(A) 15 Deviation from set nominal set current(%) 0 10 15 20 25 30 Supply Voltage VIN(V) www.belling.com.cn Belling Proprietary Information. Unauthorized Photocopy and Duplication Prohibited ©2010 Belling All Rights Reserved 7 BL9580 36V, 1.4A Step-down High Brightness LED Driver with Internal Switch Output Current Vs. Supply Voltage L=100uH 1.02 1.00 5 4 VADJ(V) Output Current(A) 6 1LED 2LED 3LED 4LED 5LED 6LED 1.01 0.99 3 0.98 2 0.97 1 0.96 5 VADJ Vs. Supply Voltage L=33uH 10 15 20 25 0 30 0 5 10 Supply Voltage VIN(V) Supply Current Vs. Supply Voltage L=33uH 250 15 20 25 30 Supply Voltage VIN(V) Shutdown Current Vs. Supply Voltage 60 50 Shutdown Current(uA) Supply Current(uA) 200 150 100 50 0 40 30 20 10 0 0 5 10 15 20 25 30 0 5 10 15 20 25 30 Supply Voltage VIN(V) Supply Voltage VIN(V) LED Current Vs. VADJ LX Switch "on" Resistance Vs. Temperature 0.60 1.2 0.55 "on" Resistance( Ω ) LED Current(A) 1.0 0.8 0.6 0.4 0.50 0.45 0.40 0.35 0.30 0.2 0.0 0.0 0.25 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 0.20 -50 PPMIC BU BL9580 Rev 1.7 5/2010 0 50 100 150 Ambient Temperature(°C) ADJ Pin Voltage(V) www.belling.com.cn Belling Proprietary Information. Unauthorized Photocopy and Duplication Prohibited ©2010 Belling All Rights Reserved 8 BL9580 36V, 1.4A Step-down High Brightness LED Driver with Internal Switch VADJ Vs.Temperature L=47uH Voltage across RSENSE Vs. Temperature L=47uH 5.00 112 12V, single LED, RS=0.15 12V, three LED, RS=0.33 24V, single LED, RS=0.15 24V, three LED, RS=0.33 108 VSENSE(mV) ADJ Pin Voltage(V) 4.95 4.90 4.85 12V, single LED, RS=0.15 12V, three LED,RS=0.33 24V, single LED,RS=0.15 24V, three LED,RS=0.33 4.80 4.75 -50 -25 0 25 50 104 100 75 100 125 96 -50 150 -25 0 Ambient Temperature(°C) 4 0 -4 -50 -25 0 25 50 75 PPMIC BU 5/2010 100 125 150 100 125 150 24V, single LED, RS=0.15 24V, three LED, RS=0.33 8 4 0 -4 -50 -25 0 25 50 75 100 125 150 Ambient Temperature(°C) Ambient Temperature(°C) BL9580 Rev 1.7 75 12 12V, single LED, RS=0.15 12V, three LED, RS=0.33 8 50 Output Current Change Vs. Temperature L=47uH Output Current Change Vs. Temperature L=47uH Deviation from nominal set value(%) Deviation from nominal set value(%) 12 25 Ambient Temperature(°C) www.belling.com.cn Belling Proprietary Information. Unauthorized Photocopy and Duplication Prohibited ©2010 Belling All Rights Reserved 9 BL9580 36V, 1.4A Step-down High Brightness LED Driver with Internal Switch Operation Description The device, in conjunction with the coil (L1) and current sense resistor (RS), forms a self oscillating continuous-mode buck converter. 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 on an internal switch 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 (VISENSE) across RS. When (VIN-VISENSE) > 115mV, the output of comparator switches low and the switch turns off. The current flowing on the RS decreases at another rate. When (VINVISENSE) < 85mV, the switch turns on again and the mean current on the LED is determined by ( 85 + 115 )mV / RS = 100mV / RS 2 The high-side current-sensing scheme and on-board current-setting circuitry minimize the number of external components while delivering LED current with ±3% accuracy, using a 1% sense resistor. The BL9580 allows dimming with a PWM signal at the ADJ input. A logic level below 0.2V at ADJ forces BL9580 to turn off the LED and the logic level at ADJ must be at least 1.2V (1.5V recommended) to turn on the full LED current. The frequency of PWM dimming ranges from 100Hz to more than 20 kHz. The ADJ pin can be driven by an external DC voltage (VADJ) to adjust the output current to a value below the nominal PPMIC BU BL9580 Rev 1.7 5/2010 average value defined by RS. The DC voltage is valid from 0.3V to 1.2V. When the dc voltage is higher than 1.2V, the output current keeps constant. The LED current also can be adjusted by a resistor connected to the ADJ pin. An internal pullup resistor (typical 1.0 MΩ) is connected to a 5V internal regulator. The voltage of ADJ pin is divided by the internal and external resistor. The ADJ pin is pulled up to the internal regulator (5V) by a 1.0 MΩ resistor. It can be floated at normal working. When a voltage applied to ADJ falls below the threshold (0.2V nom.), the output switch is turned off. The internal regulator and voltage reference remain powered during shutdown to provide the reference for the shutdown circuit. Quiescent supply current during shutdown is nominally 50uA and switch leakage is below 5uA. Additionally, to ensure the reliability, the BL9580 is built with a thermal shutdown (TSD) protection and a thermal pad. The TSD protests the IC from over temperature (160℃). Also the thermal pad enhances power dissipation. As a result, the BL9580 can handle a large amount of current safely. Application 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: IOUT = 0.1 RS This equation is valid when ADJ pin is float www.belling.com.cn Belling Proprietary Information. Unauthorized Photocopy and Duplication Prohibited ©2010 Belling All Rights Reserved 10 BL9580 36V, 1.4A Step-down High Brightness LED Driver with Internal Switch Nominal average output current (mA) 1000 760 667 333 RS(Ω) 0.1 0.13 0.15 0.3 Output current adjustment by PWM control A Pulse Width Modulated (PWM) signal with duty cycle PWM can be applied to the ADJ pin, as shown below, to adjust the output current to a value below the nominal average value set by resistor RS: IOUT = IOUT = 0.1× D (0 ≤ D ≤ 100%,1.2V ≤ VADJ ≤ 5V ) RS VPULSE × 0.1× D (0 ≤ D ≤ 100%, 0.3V ≤ VPULSE ≤ 1.2V ) 1.2 × RS RS 1 VIN The ADJ pin can be driven by an external dc voltage (VADJ), as shown, to adjust the output current to a value below the nominal average value defined by RS. RS 1 L1 2 47uH Output current adjustment by external DC control VIN L1 2 VIN CIN 4.7uF PWM ADJ 2 1 D1 ISENSE U1 LX or applied with a voltage higher than 1.2V (must be less than or equal to 5V). Actually, RS sets the maximum average current which can be adjusted to a less one by dimming. The table below gives values of nominal average output current for several preferred values of current setting resistor (RS) in the typical application circuit shown on page 1. BL9580 GND 47uH 2 VADJ BL9580 GND ADJ LX VIN CIN 4.7uF 1 D1 ISENSE U1 The average output current is given by: IOUT = 0.1× VADJ (0.3V ≤ VADJ ≤ 1.2V ) 1.2 × RS Note that 100% brightness setting corresponds to: (1.3V≤VADJ≤5V) PPMIC BU BL9580 Rev 1.7 5/2010 PWM dimming provides reduced brightness by modulating the LED’s forward current between 0% and 100%. The LED brightness is controlled by adjusting the relative ratios of the on time to the off time. A 25% brightness level is achieved by turning the LED on at full current for 25% of one cycle. To ensure this switching process between on and off state is invisible by human eyes, the switching frequency must be greater than 100 Hz. Above 100 Hz, the human eyes average the on and off times, seeing only an effective brightness that is proportional to the LED’s on-time duty cycle. The advantage of PWM dimming is that the forward current is always constant; www.belling.com.cn Belling Proprietary Information. Unauthorized Photocopy and Duplication Prohibited ©2010 Belling All Rights Reserved 11 BL9580 36V, 1.4A Step-down High Brightness LED Driver with Internal Switch therefore the LED color does not vary with brightness as it does with analog dimming. Pulsing the current provides precise brightness control while preserving the color purity. The dimming frequency of BL9580 can be as high as 20 kHz. Taking the ADJ pin to a voltage below 0.2V will turn off the output and the supply current will fall to a low standby level of 50μA nominal. 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. A suitable Murata capacitor would be GRM42-2X7R475K-50. The following web sites are useful when finding alternatives: www.murata.com www.t-yuden.com www.avxcorp.com Soft-start Inductor selection An external capacitor from the ADJ pin to ground will provide soft-start delay, by increasing the time taken for the voltage on this pin to rise to the turn-on threshold. Adding capacitance increases this delay by approximately 0.06ms/nF. Recommended inductor values for the BL9580 are in the range 27uH to 100uH. Higher values of inductance are recommended at lower output current 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. Suitable coils for use with the BL9580 are listed in the table below: Shutdown mode Inherent open-circuit LED protection If the connection to the LED(s) is opencircuited, the coil is isolated from the LX pin of the chip, so the device will not be damaged. 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 4.7uF 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. The input capacitor should be placed PPMIC BU BL9580 Rev 1.7 5/2010 Part No. MSS1038333 MSS1038473 MSS1038683 MSS1038104 L (uH) DCR (Ω) ISAT (A) 33 0.093 2.3 47 0.128 2 68 0.213 1.6 100 0.304 1.3 www.belling.com.cn Belling Proprietary Information. Unauthorized Photocopy and Duplication Prohibited ©2010 Belling All Rights Reserved Manufacturer CoilCraft www.coilcraft.com 12 BL9580 36V, 1.4A Step-down High Brightness LED Driver with Internal Switch LX Switch 'Off' time TOFF = L × ΔI VLED + VD + IAVG ( RS + RL) Where: L is the coil inductance (H) RL is the coil resistance (Ω) RS is the current sense resistance (Ω) IAVG is the required LED current (A) ΔI is the coil peak-peak ripple current (A) (Internally set to 0.3 x IAVG) VIN is the supply voltage (V) VLED is the total LED forward voltage (V) RLX is the switch resistance (Ω) (=0.35Ω nominal) VD is the diode forward voltage at the required load current (V) Reducing output ripple Peak to peak ripple current in the LED(s) can be reduced, if required, by shunting a capacitor CLED across the LED(s) as shown below: RS PPMIC BU BL9580 Rev 1.7 5/2010 L1 2 47uH CLED 1uF 2 U1 CIN 4.7uF Diode selection 1 D1 BL9580 GND ADJ For maximum efficiency and performance, the rectifier (D1) should be a fast low capacitance Schottky diode with low reverse leakage at the maximum operating voltage and temperature. They also provide better efficiency than silicon diodes, due to a combination of lower forward voltage and reduced recovery time. It is important to select parts with a peak current rating above the peak coil current and a continuous current rating higher than 1 VIN LX L × ΔI VIN − VLED − IAVG × ( RS + RL + RLX ) ISENSE TON = the maximum output load current. It is very important to consider the reverse leakage of the diode when operating above 85°C. Excess leakage will increase the power dissipation in the device and if close to the load may create a thermal runaway condition. The higher forward voltage and overshoot due to reverse recovery time in silicon diodes will increase the peak voltage on the LX output. If a silicon diode is used, care should be taken to ensure that the total voltage appearing on the LX pin including supply ripple, does not exceed the specified maximum value. The following web sites are useful when finding alternatives: www.onsemi.com VIN 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. The following equations can be used as a guide. LX Switch 'On' time A value of 1uF will reduce the supply ripple current by a factor three (approx.). Proportionally lower ripple can be achieved with higher capacitor values. Note that the capacitor will not affect operating frequency or efficiency, but it will increase start-up delay and reduce the frequency of www.belling.com.cn Belling Proprietary Information. Unauthorized Photocopy and Duplication Prohibited ©2010 Belling All Rights Reserved 13 BL9580 36V, 1.4A Step-down High Brightness LED Driver with Internal Switch dimming, by reducing the rate of rise of LED voltage. By adding this capacitor the current waveform through the LED(s) changes from a triangular ramp to a more sinusoidal version without altering the mean current value. excessive parasitic output capacitance on the switch output. Max. Power Dissipation 1600 1400 Operation at low supply voltage The internal regulator disables the drive to the switch until the supply has risen above the startup threshold (VUVLO). Above this threshold, the device will start to operate. However, with the supply voltage below the specified minimum value, the switch duty cycle will be high and the device power dissipation will be at a maximum. Care should be taken to avoid operating the device under such conditions in the application, in order to minimize the risk of exceeding the maximum allowed die temperature. (See next section on thermal considerations). The drive to the switch is turned off when the supply voltage falls below the under-voltage threshold (VUVLO0.2V). This prevents the switch working with excessive 'on' resistance under conditions where the duty cycle is high. Thermal considerations When operating the device at high ambient temperatures, or when driving maximum load current, care must be taken to avoid exceeding the package power dissipation limits. The graph below gives details for power derating. This assumes the device to be mounted on a 25mm2 PCB with 1oz copper standing in still air. Note that the device power dissipation will most often be a maximum at minimum supply voltage. It will also increase if the efficiency of the circuit is low. This may result from the use of unsuitable coils, or PPMIC BU BL9580 Rev 1.7 5/2010 Power(mW) 1200 1000 800 600 400 200 0 -40 -20 0 20 40 60 80 100 120 140 Ambient Temperature Thermal compensation of output current High luminance LEDs often need to be supplied with a temperature compensated current in order to maintain stable and reliable operation at all drive levels. The LEDs are usually mounted remotely from the device, so internal circuits for the BL9580 have been optimized to minimize the change in output current when no compensation is employed. If output current compensation is required, it is possible to use an external temperature sensing network - normally using Negative Temperature Coefficient (NTC) thermistors and/or diodes, mounted very close to the LED(s). The output of the sensing network can be used to drive the ADJ pin in order to reduce output current with increasing temperature. Thermal shutdown protection To ensure the reliability, the BL9580 is built with a thermal shutdown (TSD) protection function. The TSD protests the IC from over temperature (160℃). When the chip www.belling.com.cn Belling Proprietary Information. Unauthorized Photocopy and Duplication Prohibited ©2010 Belling All Rights Reserved 14 BL9580 36V, 1.4A Step-down High Brightness LED Driver with Internal Switch temperature decreases (140℃), the IC recovers again. Layout considerations Careful PCB layout is critical to achieve low switching losses and stable operation. Use a multilayer board whenever possible for better noise immunity. Minimize ground noise by connecting high-current ground returns, the input bypass-capacitor ground lead, and the output-filter ground lead to a single point (star ground configuration). LX pin The LX pin of the device is a fast switching node, so PCB tracks should be kept as short as possible. To minimize ground 'bounce', the ground pin of the device should be soldered directly to the ground plane. when left floating, PCB traces to this pin should be as short as possible to reduce noise pickup. ADJ pin can also be connected to a voltage between 1.2V~5V. In this case, the internal circuit will clamp the output current at the value which is set by ADJ=1.2V. High voltage traces Avoid running any high voltage traces close to the ADJ pin, to reduce the risk of leakage due to board contamination. Any such leakage may raise the ADJ pin voltage and cause excessive output current. A ground ring placed around the ADJ pin will minimize changes in output current under these conditions. Coil and decoupling capacitors and current sense resistor It is particularly important to mount the coil and the input decoupling capacitor as close to the device pins as possible to minimize parasitic resistance and inductance, which will degrade efficiency. It is also important to minimize any track resistance in series with current sense resistor RS. It’s best to connect VIN directly to one end of RS and ISENSE directly to the opposite end of RS with no other currents flowing in these tracks. It is important that the cathode current of the Schottky diode does not flow in a track between RS and VIN as this may give an apparent higher measure of current than is actual because of track resistance. ADJ pin The ADJ pin is a high impedance input, so PPMIC BU BL9580 Rev 1.7 5/2010 www.belling.com.cn Belling Proprietary Information. Unauthorized Photocopy and Duplication Prohibited ©2010 Belling All Rights Reserved 15 BL9580 36V, 1.4A Step-down High Brightness LED Driver with Internal Switch Package Description Symbol A b b1 B C C1 D D1 e H Dimensions In Millimeters Min Dimensions In Inches Max Min Max 1.397 1.600 0.356 0.508 0.406 0.533 2.388 2.591 3.937 4.242 0.787 1.194 4.394 4.597 1.397 1.702 1.500 TYP. 0.055 0.063 0.014 0.020 0.016 0.021 0.094 0.102 0.155 0.167 0.031 0.047 0.173 0.181 0.055 0.067 0.060 TYP. 0.356 0.014 0.432 0.017 SOT89-5 Surface Mount Package PPMIC BU BL9580 Rev 1.7 5/2010 www.belling.com.cn Belling Proprietary Information. Unauthorized Photocopy and Duplication Prohibited ©2010 Belling All Rights Reserved 16 BL9580 36V, 1.4A Step-down High Brightness LED Driver with Internal Switch Symbol Dimensions In Millimeters Dimensions In Inches Min Max Min Max A B C D E F H 4.80 3.80 5.80 5.00 4.00 6.20 0.188 0.149 0.228 0.197 0.158 0.244 0.33 0.10 1.35 0.51 0.25 1.75 0.013 0.004 0.053 0.020 0.010 0.069 K 0.19 0.25 0.007 0.010 M 0.40 1.27 0.016 0.050 α 0º 8º 0º 8º 1.27 BSC 0.050 SOP-8 Surface Mount Package PPMIC BU BL9580 Rev 1.7 5/2010 www.belling.com.cn Belling Proprietary Information. Unauthorized Photocopy and Duplication Prohibited ©2010 Belling All Rights Reserved 17