DATA SHEET Part No. AN30888B Package Code No. ∗QFN016-P-0304B Publication date: May 2010 SDG00005AEB 1 AN30888B Contents Overview ………………………………………….………………………………………………………………… 3 Features ……………………………………………………………………………………………………………. 3 Applications …………………………………………………………………………………………………………. 3 Package ……………………………………………………………………………………………………………. 3 Type ………………………………………………………………………………………………………………… 3 Application Circuit Example (Block Diagram) …………………………………………………………………… 4 Pin Descriptions …………………………………………………………………………………………………… 7 Absolute Maximum Ratings ……………………………………………………………………………………… 8 Operating Supply Voltage Range ……………………………………………………………………………….. 8 Allowable Voltage Range………………………………………………………………………………...………… 9 Electrical Characteristics …………………………………………………………………………………………. 10 Electrical Characteristics (Reference values for design) ………………………………………………………. 11 Control Pin Mode Table …………………………………………………………………………………………… 12 Electrical Characteristics Test Procedures ……………………………………………………………………... 13 Technical Data …………………………….………………………………...……………………………………… 16 y I/O block circuit diagrams and pin function descriptions ………………………………………………………. 16 y Functions and properties descriptions ………………………………………………………….………………. 19 y PD ⎯ Ta diagram …………………………………………………………………………………………………. 29 Usage Notes ………………………………..……….……………………………………………………………… 30 y Special attention and precaution in using ……………………………………………..………………………… 30 SDG00005AEB 2 AN30888B AN30888B High Brightness LED Driver IC Overview AN30888B is a Boost/Buck-Boost/Buck DCDC controller that drives an external power NMOS switch. It is suitable for driving high brightness LED for LED lighting applications. Features y Battery operation : 3 V to 15 V y Output current range : 0 A to a few Amperes depending on rating of external NMOS and mode of operation y Current mode control architecture y LED dimming function available by using PWM signal y 30 mV / 200 mV reference voltage y Low standby current y Configurable as either Boost/Buck-Boost/ Buck mode converter y Built-in various protection circuit : Under voltage lock out Over voltage protection Soft start function Applications y LED lighting module y LED lantern applications y White LED backlighting for LCD panel y White LED flash light driving applications y General LED back lighting Package y 16 pin Plastic Quad Flat Non-leaded Package (QFN Type) Type y Bi–CMOS IC SDG00005AEB 3 AN30888B Application Circuit Example (Block Diagram) y Boost Mode VIN 14 VREG L 1 BGR ENB 12 2.2 μF 1 μF 3.65 V 9 SW EN UVLO CONTROL PWM D VREG 1.262 V VIN VOUT 4 CS 10 IPK ILED VFB RCS 7 GNDP R1 VFB_SEL 2 Reference voltage 6 OVP GND 15 R2 Notes) y This application circuit is an example. The operation of mass production set is not guaranteed. Perform enough evaluation and verification on the design of mass production set. y Use external resistor with ±1% accuracy at CS pin. y Use ceramic type capacitor (Typ. 1 μF, Min. 0.5 μF) at VREG pin. y Use schottky diode at VOUT. y This block diagram is for explaining functions. The part of the block diagram may be omitted, or it may be simplified. SDG00005AEB 4 AN30888B Application Circuit Example (Block Diagram) (continued) y Buck-Boost Mode L VOUT D VIN 14 VREG 2.2 μF 1 BGR VIN VREG 3.65 V 1.262 V ENB 12 1 μF 9 SW EN UVLO 4 CS CONTROL PWM IPK ILED VFB RCS 10 7 GNDP VFB_SEL 2 Reference voltage 6 OVP R1 GND 15 R2 Notes) y This application circuit is an example. The operation of mass production set is not guaranteed. Perform enough evaluation and verification on the design of mass production set. y Use external resistor with ±1% accuracy at CS pin. y Use ceramic type capacitor (Typ. 1 μF, Min. 0.5 μF) at VREG pin. y Use schottky diode at VOUT. y This block diagram is for explaining functions. The part of the block diagram may be omitted, or it may be simplified. SDG00005AEB 5 AN30888B Application Circuit Example (Block Diagram) (continued) VIN 14 VREG y Buck Mode 1 BGR ENB 12 2.2 μF L 3.65 V 9 SW EN UVLO IPK CONTROL PWM D VREG 1.262 V VIN 1 μF 4 CS ILED VFB VOUT RCS 10 7 GNDP VFB_SEL 2 Reference voltage GND 15 6 OVP Notes) y This application circuit is an example. The operation of mass production set is not guaranteed. Perform enough evaluation and verification on the design of mass production set. y Use external resistor with ±1% accuracy at CS pin. y Use ceramic type capacitor (Typ. 1 μF, Min. 0.5 μF) at VREG pin. y Use schottky diode at VOUT. y This block diagram is for explaining functions. The part of the block diagram may be omitted, or it may be simplified. SDG00005AEB 6 AN30888B Pin Descriptions Pin No. Pin name Type Description 1 VIN Power Supply 2 VFB_SEL Input 3 N.C. — 4 CS Input 5 N.C. — 6 OVP Input 7 GNDP Ground 8 N.C. — 9 SW Output 10 PWM Input 11 N.C. — 12 ENB Input 13 N.C. — 14 VREG Output Regulator Output 15 GND Ground Ground 16 N.C. — Power Supply of IC Feedback voltage select — Current Sense — Over Voltage Protection input pin for Boost mode; Connect to GND for Buck mode Power Ground — External NMOS Transistor Gate Drive PWM Dimming Control — Standby On/Off Control — — SDG00005AEB 7 AN30888B Absolute Maximum Ratings Note) Absolute maximum ratings are limit values which do not result in damages to this IC, and IC operation is not guaranteed at these limit values. A No. Parameter Symbol Rating Unit Notes 1 Supply voltage VDD 15.5 V *1 2 GND pin current IGND — A — 3 Power dissipation PD 100 mW *2 4 Operating ambient temperature Topr –25 to +85 °C *3 5 Storage temperature Tstg –55 to +125 °C *3 Notes) *1 : The values under the condition not exceeding the above absolute maximum ratings and the power dissipation. *2 : The power dissipation shown is the value at Ta = 85°C for the independent (unmounted) IC package without a heat sink. When using this IC, refer to the • PD-Ta diagram in the Technical Data and design the heat radiation with sufficient margin so that the allowable value might not be exceeded based on the conditions of power supply voltage, load, and ambient temperature. *3 : Except for the power dissipation, operating ambient temperature, and storage temperature, all ratings are for Ta = 25°C. Operating Supply Voltage Range Parameter Symbol Range Unit Notes Supply voltage range VIN 3.0 to 15 V *1 Supply voltage range (Boost Mode/Buck-Boost Mode) VIN1 3.0 to 12 V *1 Supply voltage range (Buck Mode) VIN2 3.0 to 15 V *1 Note) *1 : The values under the condition not exceeding the above absolute maximum ratings and the power dissipation. SDG00005AEB 8 AN30888B Allowable Voltage Range Notes) y Allowable current and voltage ranges are limit ranges which do not result in damages to this IC, and IC operation is not guaranteed within these limit ranges. y Voltage values, unless otherwise specified, are with respect to GND. y VIN is voltage for VIN pin. y Do not apply external currents or voltages to any pin not specifically mentioned. Pin No. Pin name Rating Unit Note 1 VIN –0.3 to 15 V *1 2 VFB_SEL –0.3 to 5.5 V — 4 CS –0.3 to VREG V *2 6 OVP –0.3 to VREG V *2 9 SW –0.3 to VREG V *2 10 PWM –0.3 to 5.5 V *2 12 ENB –0.3 to VIN V *1 14 VREG –0.3 to 4.3 V *2 Notes) *1 : VIN must not exceed 15 V. *2 : VREG must not exceed 4.3 V. SDG00005AEB 9 AN30888B Electrical Characteristics at VIN = 6 V, ENB = 6 V, PWM = VREG Note) Ta = 25°C±2°C unless otherwise specified. B No. Parameter Symbol Conditions Limits Min Typ Max Unit Notes Circuit Current Consumption 1 Standby Current ISTB ENB = 0 V — — 10 μA — 2 Operating Quiescent Current ICC ENB = VIN No load condition — — 1 mA — ENABLE (ENB), VFB_SEL and PWM Control Function 3 ENB High Input Logic VENBH — 3 — VIN V — 4 ENB Low Input Logic VENBL — 0 — 0.3 V — 5 VFB_SEL High Input Logic VVFBSELH — 0.7 × VREG — 5 V — 6 VFB_SEL Low Input Logic VVFBSELL — 0 — 0.3 × VREG V — 7 PWM High input Logic VPWMH — 0.7 × VREG — 5 V — 8 PWM Low input Logic VPWML — 0 — 0.3 × VREG V — — — 25 μA — Input Pin Current Consumption 9 Enable Pin Current IENB ENB = 6 V Output Driver 10 SW High Output Logic VSWH SW output High logic; MOSFET ON condition 0.7 × VREG — VREG +0.2 V — 11 SW Low Output Logic VSWL SW output Low logic; MOSFET OFF condition –0.2 — 0.2 V — Under Voltage Lock Out (UVLO) 12 Under Voltage protection on value VUVLOON VIN Falling SW OFF; VREG = No load 1.9 2.1 2.3 V — 13 Under voltage protection Hysteresis VUVLOHYS VIN Rising SW ON – VIN Falling SW OFF; VREG = No load 0.1 0.3 0.5 V — SDG00005AEB 10 AN30888B Electrical Characteristics (Reference values for design) at VIN = 6 V Note) The characteristics listed below are reference values derived from the design of the IC and are not guaranteed by inspection. If a problem does occur related to these characteristics, we will respond in good faith to user concerns. B No. Parameter Symbol Conditions Reference values Min Typ Max Unit Notes Reference Voltage Control 14 VFB Reference Voltage 1 VVFB1 VFB_SEL = High OVP = 0 V (Buck mode) 196 202 208 mV — 15 VFB Reference Voltage 2 VVFB2 VFB_SEL = Low OVP = 0 V (Buck mode) 24 32 40 mV — VOVP R1 = 470 kΩ, R2 = 30 kΩ 18 21 24 V — Fix off time at SW pin 0.5 1 2 μs — — — 1.5 MHz — 3.45 3.65 3.85 V — — 90 — % — Over Voltage Protection (Boost Mode Only) 16 Over Voltage Protection Threshold Output Driver 17 Driver Off Time TOFF 18 Maximum Operating Frequency FMax — Regulator Voltage (VREG) 19 VREG Output Voltage VREG 4 V ≤ VIN ≤ 15 V No Load Condition, CVREG = 1 μF Efficiency 20 Efficiency Eff VIN = 6 V 1 LED of VF = 3.7 V ILED = 400 mA VFB_SEL = High OVP = 0 V (Buck mode) SDG00005AEB 11 AN30888B Control Pin Mode Table Note) See parameters B No. 3, 4, 5, 6, 7 and 8 in the Electrical Characteristics for control voltage ranges. Pin No. Description Pin voltage Low High 2 VFB_SEL ON/OFF VFB = 32 mV VFB = 202 mV 10 PWM ON/OFF PWM OFF PWM ON 12 ENB ON/OFF STANDBY OPERATING Remarks Feedback voltage selection When PWM is not used, the pin is left floating Standby / Operating mode control SDG00005AEB 12 AN30888B Electrical Characteristics Test Procedures C No. Input Parameter Pin No. Output Conditions Pin No. Conditions Switch S1 S2 S3 S4 S5 S6 Circuit Current Consumption 1 2 Standby Current 12 10 2 6 4 9 ENB = 0 V PWM = 0 V VFB_SEL = 0 V OVP = 0 V CS = 0 V SW = Hi-Z 4 Standby current consumption 5 5 5 2 2 1 Operating Quiescent Current 12 10 2 6 4 9 ENB = VIN PWM = 0 V VFB_SEL = 0 V OVP = 0 V CS = 0 V SW = Hi-Z 4 Current consumption 2 5 5 2 2 1 ENABLE (ENB), VFB_SEL and PWM Control Function 3 4 5 6 7 ENB High Input Logic 12 10 2 6 4 9 ENB = 0.30 V PWM = Hi-Z VFB_SEL = 3.65 V OVP = 0 V CS = 0 V SW = Hi-Z 16 Output DC voltage 3 1 2 2 2 1 ENB Low Input Logic 12 10 2 6 4 9 ENB = 3.0 V PWM = Hi-Z VFB_SEL = 3.65 V OVP = 0 V CS = 0 V SW = Hi-Z 16 Output DC voltage 4 1 2 2 2 1 VFB_SEL High Input Logic 12 10 2 6 4 9 ENB = VIN PWM = Hi-Z VFB_SEL = 0.70× VREG OVP = 0 V CS = 100 mV SW = Hi-Z 11 Output DC voltage / 1 MHz 2 1 3 2 3 1 VFB_SEL Low Input Logic 12 10 2 6 4 9 ENB = VIN PWM = Hi-Z VFB_SEL = 0.30 × VREG OVP = 0 V CS = 100 mV SW = Hi-Z 11 Output DC voltage / 1 MHz 2 1 4 2 3 1 PWM High input Logic 12 10 2 6 4 9 ENB = VIN PWM = 0.70 × VREG VFB_SEL = 3.65 V OVP = 0 V CS = 0 V SW = Hi-Z 11 Output DC voltage / 1 MHz 2 3 2 2 2 1 SDG00005AEB 13 AN30888B Electrical Characteristics Test Procedures (continued) Input C No. 8 Parameter Pin No. Output Conditions Switch Pin No. Conditions S1 S2 S3 S4 S5 S6 12 10 2 6 4 9 ENB = VIN PWM = 0.30 × VREG VFB_SEL = 3.65 V OVP = 0 V CS = 0 V SW = Hi-Z 11 Output DC voltage / 1 MHz 2 4 2 2 2 1 12 10 2 6 4 9 ENB = VIN PWM = Hi-Z VFB_SEL = 0 V OVP = 0 V CS = 0 V SW = Hi-Z 14 Current Consumption 2 1 5 2 2 1 SW High Output Logic 12 10 2 6 4 9 ENB = VIN PWM = 3.65 V VFB_SEL = 3.65 V OVP = 0 V CS = 0 V SW = 0 A 11 Output DC voltage / 1 MHz 2 2 2 2 2 2 SW Low Output Logic 12 10 2 6 4 9 ENB = VIN PWM = 0 V VFB_SEL = 3.65 V OVP = 0 V CS = 0 V SW = 0 A 11 Output DC voltage / 1 MHz 2 5 2 2 2 2 PWM Low input Logic Input Pin Current Consumption 9 Enable Pin Current Output Driver 10 11 SDG00005AEB 14 AN30888B Electrical Characteristics Test Procedures (continued) C No. Input Parameter Pin No. Output Conditions Switch Pin No. Conditions S1 S2 S3 S4 S5 S6 Under voltage Lock Out (UVLO) 12 13 Under voltage protection on value 12 10 2 6 4 9 ENB = VIN PWM = Hi-Z VFB_SEL = 3.65 V OVP = 0 V CS = 0 V SW = Hi-Z 11 Output DC voltage / 1 MHz 2 1 2 2 2 1 Under voltage protection Hysteresis 12 10 2 6 4 9 ENB = VIN PWM = Hi-Z VFB_SEL = 3.65 V OVP = 0 V CS = 0 V SW = Hi-Z 11 Output DC voltage / 1 MHz 2 1 2 2 2 1 SDG00005AEB 15 AN30888B Technical Data y I/O block circuit diagrams and pin function descriptions Note) The characteristics listed below are reference values derived from the design of the IC and are not guaranteed. Pin No. Waveform and voltage Internal circuit Impedance 1 DC (3 V to 15 V) — Z : Low Description VIN Power Supply of IC VREG 14 2 3 DC (0 V to 5 V) VFB_SEL 2 200 VFB_SEL Z : Hi-Z Feedback voltage select pin — — — No connection VREG 14 4 5 DC (0 V to 250 mV) — CS CS 4 500 Z : Hi-Z Current Sense Pin — — SDG00005AEB No connection 16 AN30888B Technical Data (continued) y I/O block circuit diagrams and pin function descriptions (continued) Note) The characteristics listed below are reference values derived from the design of the IC and are not guaranteed. Pin No. Waveform and voltage Internal circuit Impedance Description VREG 14 OVP OVP 6 6 1k DC (0 V to 1.26 V) Z : Hi-Z 1k Over Voltage Protection input pin for Boost and Buck-Boost mode Connect to GND for Buck mode 7 GNDP — — Power Ground 8 — — — No connection VREG 14 9 SW 9 Pulse (0 V to 3.65 V) VREG SW Z : Hi-Z External NMOS Transistor Gate Driving Pulse VREG 167k 10 11 Pulse (0 V to 5 V) — PWM 10 PWM 3k Z : 170 kΩ PWM Dimming Control — — SDG00005AEB No connection 17 AN30888B Technical Data (continued) y I/O block circuit diagrams and pin function descriptions (continued) Note) The characteristics listed below are reference values derived from the design of the IC and are not guaranteed. Pin No. Waveform and voltage Internal circuit Impedance Description ENB 12 2k 12 DC (3 V to 15 V) ENB 200k Z : 402 kΩ Standby On/Off Control Pin 2k 200k 13 — 20k — — No connection VIN 1 14 DC (Typ. 3.65 V) VREG Z : Hi-Z Regulator Output Pin VREG 14 550 550 550 15 GND — — Signal Ground 16 — — — No connection SDG00005AEB 18 AN30888B (V *)Nout VIN = − F LEDs Technical Data (continued) Vout )*(N VIN = − VF LEDs y Functions and properties descriptions (1) Overview AN30888B is a constant current LED driver. The IC works as a Boost /Buck-Boost/ Buck mode DCDC controller with external MOSFET. Operating input voltages ranges from 3 V to 15 V. The mode of operation depends on the number of LEDs to be driven and the supply voltage level. In general, please adhere to the following: If total LED voltage drop is more than supply voltage, boost mode is adopted. If LED voltage drop is less than the supply voltage, buck mode is adopted . If supply voltage is close to the total LED voltage drop, the Buck-Boost mode can be used. Please note that the different mode of operation should be manually configured. Output LED current can be designed ranges from 0 A and to a few amperes depending on the mode of operation, the external MOSFET characteristic and feasible RCS value used. The control architecture uses current mode fix off time control. The VFB reference voltage determines LED current by setting VFB_SEL pin with values of 32 mV or 202 mV under buck mode. By applying VFB voltage of 32 mV, user can achieve higher efficiency with lower power dissipation in RCS resistor. Applying 202 mV VFB voltage achieves better LED current accuracy. (2) Standby enable function AN30888B enters standby mode when ENB pin is pulled low. During standby, the IC draws a small current of value less than 10 μA from the power supply. This helps to achieve longer battery usage time. During Boost mode operation, although external MOSFET cannot be turned on at standby condition, there is still a DC current path between the input and the LEDs through the inductor and schottky diode. Thus it is important to make sure that during boost mode, the minimum forward voltage of the LED array must exceed the maximum input voltage to ensure the LEDs remain off during standby mode. SDG00005AEB 19 AN30888B (V *)Nout VIN = − F LEDs Technical Data (continued) Vout )*(N VIN = − VF LEDs y Functions and properties descriptions (continued) (3) Internal regulator An internal 3.65 V regulator is used as the power supply for internal core circuit of this IC. This regulated voltage, VREG will be provided when VIN is approximately in the range of 4 V to 15V. For VIN lower than 4 V, regulator will act as a VIN voltage follower, with output voltage close to VIN. The amount of drop voltage from VIN during VIN follower mode depends on load current of the regulator and also tolerance of the IC. In general, the regulator output voltage will be approximately 0.3 V lower than VIN during this mode of operation. This regulator requires a capacitor of 1 μF to be connected to VREG pin. This capacitor helps to provide a stable regulated voltage to the IC. The regulator has a current ability of approximately 15 mA. However, it is not designed to provide as external power supply voltage. Hence an external load exceeding approximately 0.5 mA to the VREG pin is not allowed. (4) Output setting consideration The output voltage, VOUT is set using the following equations for both boost and buck mode: VOUT = (VF × NLEDs + VD) ……………………………………………… Eq[1] (Boost mode) VOUT = (VIN – VF × NLEDs) ……………………………………………… Eq[2] (Buck mode) VOUT = (VF × NLEDs + VD+VIN) ………………………………………… (Buck-Boost mode) VIN : VF : NLEDs : VD : Eq[3] Battery or Input power supply voltage LED forward drop voltage Number of LEDs stacked in series Schottky diode forward drop voltage For Boost mode or Buck-Boost mode operation, VOUT setting should be lesser than Drain–Source breakdown voltage of external MOSFET as mention in (11). Also VOUT should be lesser than OVP protection threshold as mentioned in (9). For Buck mode operation, VOUT setting should give sufficient voltage for external MOSFET to operate properly at the required output current setting. SDG00005AEB 20 AN30888B Technical Data (continued) y Functions and properties descriptions (continued) (5) Feedback voltage VFB at CS pin The VFB voltage is generated internally in the IC and output at CS pin. This voltage allows users to fix the input peak current, IPK as well as the LED output current, ILED. This voltage will change according to the setting at VFB_SEL pin. For operation in boost mode/buck-boost mode, VFB will be inversely proportionally to supply voltage, VIN. When input supply voltage decreases, VFB will increase. This ensure LED current remain accurate as supply voltage decreases. When operating in buck mode, VFB voltage will remain at 202 mV or 32 mV depending on whether VFB_SEL pin is high or low. The following are some figures of VFB voltage with respect to VIN. For detail information, please refer to graph and data table information as the following. For Boost mode and Buck-Boost mode : VFB = 116 mV (When VFB_SEL = High ; VIN = 6 V) VFB = 50 mV (When VFB_SEL = Low ; VIN = 6 V) VFB = 198.3 mV (When VFB_SEL = Low ; VIN = 3 V) VFB = 88 mV (When VFB_SEL = Low ; VIN = 3 V) For Buck mode : VFB = 202 mV VFB = 32 mV (When VFB_SEL = High, for all VIN level) (When VFB_SEL = Low, for all VIN level) To improve overall efficiency VFB voltage can be set lower by switching VFB_SEL = Low. On the other hand accuracy can be improved by using VFB_SEL = High mode. SDG00005AEB 21 AN30888B Technical Data (continued) y Functions and properties descriptions (continued) (5) Feedback voltage VFB at CS pin (continued) Boost mode/ Buck-Boost mode BOOST MODE: VCS Voltage vs VIN 220.0 VIN (V) 200.0 VFB_SEL = High VFB_SEL = Low VFB_SEL = High VFB_SEL = Low VFB (mV) VFB (mV) VFB (mV) VFB (mV) 3 198.3 88.0 202 32 4 161.0 71.0 202 32 5 132.3 57.7 202 32 6 116.0 50.0 202 32 7 98.3 43.0 202 32 8 86.3 38.0 202 32 9 77.3 34.0 202 32 10 70.0 31.0 202 32 11 64.0 28.3 202 32 12 59.0 26.3 202 32 13 N.A N.A 202 32 14 N.A N.A 202 32 15 N.A N.A 202 32 180.0 VCS(mV) 160.0 140.0 120.0 VFB_SEL="H" 100.0 VFB_SEL="L" 80.0 60.0 40.0 20.0 0.0 3 5 7 9 11 VIN(V) VCS(mV) BUCK MODE: VCS Voltage vs VIN 220.0 200.0 180.0 160.0 140.0 120.0 100.0 80.0 60.0 40.0 20.0 0.0 VFB_SEL="H" VFB_SEL="L" 3 5 7 9 11 13 Buck mode 15 VIN(V) SDG00005AEB 22 AN30888B PKFB 2 * -L Eq[7] IV CS = R Technical Data (continued) = IR CS -PK y Functions and properties descriptions (continued) (6) Inductor selection Inductor value, L is set by the required inductor ripple current desired. The general trend for lower inductor value is a smaller inductor physical size, but a larger input ripple current. Similarly, an increase in inductor value will decease input ripple current. Users are advice to choose an inductor that can handle the peak current IPK, flowing across it without saturating. In addition, inductor with lower series resistance are preferred to provide better operating efficiency. The following equation gives a general guideline in selection inductor value based on 30% peak to peak ripple current across the inductor. (VOUT – VIN) × TOFF L = ————————————— ……………………… 0.3 × IIN Eq[4] (Boost mode，Buck-Boost mode) (VIN – VOUT) × TOFF L = ————————————— ……………………… 0.3 × ILED Eq[5] (Buck mode) VOUT = Output voltage VIN = Input supply voltage TOFF = Fixed off time design at 1 μs ILED = LED output current IIN is input current from supply voltage Please note that the 0.3 factor can be altered if 30% peak to peak current is changed. i.e, if percentage of peak to peak current needed is 40%, this factor will be 0.4. SDG00005AEB 23 AN30888B *2PFB -L Eq[7] IV CS = R K Technical Data (continued) -PK = IR CS y Functions and properties descriptions (continued) (7) Setting output LED current and choosing current sense resistor RCS The LED current in this IC can be set easily by selecting the appropriate RCS resistor to be used at CS pin of this chip. For Boost Mode and Buck-Boost mode : RCS resistor can be set in the following way : First is to calculate input current IIN at the required operating condition : IIN = (VOUT + VD) × (ILED / VIN) …………………………… Eq[6] (Boost mode，Buck-Boost mode) VOUT = Output voltage VD = Schottky diode forward drop voltage ILED = Required LED current VIN = Input supply voltage After which the peak input current, IPK can be determine by adding IIN with half the peak to peak ripple current at the inductor. (VOUT – VIN) × TOFF IPK = IIN + ——————————— …………………… Eq[7] 2L (Boost mode，Buck-Boost mode) TOFF = TOFF is fixed off time = 1 μs L = Inductor value found in part (6) inductor selection VOUT = Output voltage VIN = Input supply voltage IIN = IIN is input current found in Eq[6] Lastly, RCS resistor can be determine by using : VFB RCS = ——— ……………………………………………… IPK Eq[8] (Boost mode，Buck-Boost mode) VFB is voltage at CS pin. Refer to data graphs for the VFB voltage at different input voltage condition. IPK is peak current found in Eq[7] Using numeric example of operating condition : VIN = 6 V, VOUT = 10 V, ILED = 500 mA, TOFF = 1 μs, L = 16 μH, VD = 0.4 V, VFB = 0.1 V@VIN = 6 V From Eq[6] : From Eq[7] : From Eq[8] : IIN = (10 + 0.4) × (0.5 / 6) = 0.8667 A (10 – 6) × 1μ IPK = 0.8667 + ——————— = 0.9971 A 2 × 16μ 0.1 RCS = ———— = 100.8 mΩ 0.9917 SDG00005AEB 24 AN30888B Technical Data (continued) y Functions and properties descriptions (continued) (7) Setting output LED current and choosing current sense resistor RCS (continued) For Buck Mode : RCS resistor can be set in the following way : First is to calculate the peak current IPK using Eq[9]. During buck mode, peak current sense correspond to the average output LED current plus half of actual current ripple through the inductor. (VIN – VOUT) × TOFF IPK = ILED + ——————————— …………………… Eq[9] 2L (Buck mode) VOUT = Output voltage VIN = Input supply voltage TOFF =TOFF = Fixed off time design at 1 μs ILED = LED output current L = Inductor value found in part (6) inductor selection Lastly, RCS resistor can be determine by using : VFB RCS = ——— ……………………………………………… IPK Eq[10] (Buck mode) VFB is voltage at CS pin. Refer to data graphs for the VFB voltage at different input voltage condition. IPK is peak current found in Eq[9] . Using numeric example of operating condition : VIN = 12 V, VOUT = 2 V, ILED = 500 mA, TOFF = 1 μs, L = 66 μH, VFB = 0.2 V (12 – 2) × 1μ IPK = 0.5 + —————— = 0.575 A 2 × 66μ 0.2 From Eq[10] : RCS = ———— = 348 mΩ 0.575 From Eq[9] : Please note that for component deviation such as inductor, diodes, etc, these deviation can cause the designed IPK to be higher or lower than the calculated value. Users may need to fine tune the value of RCS from the calculated values in order to obtain accurate ILED measurement. Please take note of total impedance including parasitic impedance of PCB trace at CS pin to ground when designing the required RCS value. This is especially important if the designed ILED is high as RCS value will be small and in turn making parasitic impedance significant to the total impedance seen at CS pin SDG00005AEB 25 AN30888B Technical Data (continued) y Functions and properties descriptions (continued) (8) Soft start Soft start circuit is incorporated into this IC to avoid high in-rush current during start-up. After the device is enabled (ENB = High), the output inductor current and output voltage will rise slowly from initial condition. This slow start-up time ensure smooth start-up as well as minimize in-rush current. (9) Over Voltage Protection (OVP) When operating in Boost mode or Buck-Boost mode, over voltage protection is needed to prevent damages to IC or external component damages in cases of open LED condition. OVP switches off external power MOSFET to prevent output from rising over a designed OVP voltage. Output voltage should be limited to the rating of external component used. (for example Drain Source voltage rating of the external MOSFET or the output capacitor) OVP compares the internal reference voltage of 1.26 V with output voltage through resistor network. OVP threshold is set using the following equation: 1.262 V × (R1 ＋R2) VOVP = —————————— …………………… R2 Eq[11] (Boost mode，Buck-Boost mode) If R1 = 470 kΩ, R2 = 30 kΩ, OVP threshold will be designed at around 21 V. When OVP is triggered, output voltage will be clamped at this threshold voltage (with hysteresis of around 1 V to 2 V) until the fault (e.g open LED condition) has been removed. When operating in buck mode, the OVP pin must be short to ground to disable this function as OVP function is not necessary in this mode. SDG00005AEB 26 AN30888B Technical Data (continued) y Functions and properties descriptions (continued) (10) Under Voltage Lock Out (UVLO) Under Voltage lock out prevents IC from operation at supply voltage lower than 2.1 V. This function prevent IC from abnormal operation when supply voltage VIN drops below our recommended input range. When input voltage is lower than this lock out value of 2.1 V, external MOSFET will be switched off. When input voltage rises to 2.4 V or more, device operation starts again. This means a hysteresis voltage of about 0.3 V. (11) Power MOSFET consideration When selecting the power MOSFET, it is important to consider parameters such as gate-source, drain-source breakdown voltage, total gate capacitance, ON resistance and the drain current rating. When power is turned on for IC operating in boost mode, output voltage needed to drive LED will be reflected to Drain-Source voltage of the power MOSFET. Thus it is recommended to select a MOSFET that can handle this output voltage. Alternatively, output and Drain-Source voltage can be protected and clamped by OVP circuit as mentioned in point (9). Gate capacitance of the MOSFET chosen should ideally to be smaller than 3 nF. (12) PWM operation PWM signal can be generated externally and input into PWM pin of this IC. This PWM signal will turn on and off the output driver, giving an average output LED current that is proportional to the duty cycle of the PWM signal. ILED(avg.) = ILED × Duty……………………………………… Eq[12] (Boost / Buck-Boost / Buck mode) ILED(avg.) = The average output LED current after PWM is input ILED = The nominal LED current set in part (7) Duty = The ratio of on pulse time compared to total period time of the PWM signal. A PWM frequency of 1 kHz or lower is recommended to minimize error due to rise and fall time of the converter output. SDG00005AEB 27 AN30888B Technical Data (continued) y Functions and properties descriptions (continued) (13) Maximum duty operation Maximum Duty limitation is needed when operating in Boost or Buck- Boost mode. This prevents the output voltage from having abnormal operation. For Buck mode, there is no need for maximum duty limit as SW pin is able to switch to 100% duty. Please refer to the graph below for maximum duty vs VIN data for Boost and Buck-Boost mode operation. Boost/Buck-boost mode VIN (V) Duty Limit (%) 3.0 88.73 3.5 87.09 4.0 85.27 4.5 83.58 5.0 81.99 5.5 79.79 6.0 78.40 6.5 77.38 7.0 76.25 7.5 75.19 8.0 73.92 8.5 72.89 9.0 71.78 9.5 70.83 10.0 69.91 10.5 68.90 11.0 67.97 11.5 67.09 12.0 66.33 (14) Minimum duty operation Parasitic circuit capacitance, inductance and external MOSFET gate drive current can create spike in the current sense, CS pin voltage at the point when external MOSFET is switched on. In order to prevent this spike to terminate the ON time prematurely, an internal filter of time constant, 100 ns is designed in chip. This time constant of 100 ns translates to a minimum duty of around 9% for all modes of operation. To further reduce the spike in the CS voltage especially when operating in low ILED condition (example: RCS is more than 0.8 Ω or more), external RC filter can be used in between VFB node to CS pin which act as a low pass filter to filter spike noise from entering CS pin. This RC filter time constant should be long enough to reduce the parasitic spike without significantly affecting the shape of CS voltage. The recommended RC value range from : R = 10 Ω to 1 kΩ and C = 100 pF to 500 pF depending on mode of operation and spike level. SDG00005AEB 28 AN30888B Technical Data (continued) y PD ⎯ Ta diagram SDG00005AEB 29 AN30888B Usage Notes y Special attention and precaution in using 1. This IC is intended to be used for general electronic equipment [LED Lighting Devices]. Consult our sales staff in advance for information on the following applications: x Special applications in which exceptional quality and reliability are required, or if the failure or malfunction of this IC may directly jeopardize life or harm the human body. x Any applications other than the standard applications intended. (1) Space appliance (such as artificial satellite, and rocket) (2) Traffic control equipment (such as for automobile, airplane, train, and ship) (3) Medical equipment for life support (4) Submarine transponder (5) Control equipment for power plant (6) Disaster prevention and security device (7) Weapon (8) Others : Applications of which reliability equivalent to (1) to (7) is required It is to be understood that our company shall not be held responsible for any damage incurred as a result of or in connection with your using the IC described in this book for any special application, unless our company agrees to your using the IC in this book for any special application. 2. Pay attention to the direction of LSI. When mounting it in the wrong direction onto the PCB (printed-circuit-board), it might smoke or ignite. 3. Pay attention in the PCB (printed-circuit-board) pattern layout in order to prevent damage due to short circuit between pins. In addition, refer to the Pin Description for the pin configuration. 4. Perform a visual inspection on the PCB before applying power, otherwise damage might happen due to problems such as a solderbridge between the pins of the semiconductor device. Also, perform a full technical verification on the assembly quality, because the same damage possibly can happen due to conductive substances, such as solder ball, that adhere to the LSI during transportation. 5. Take notice in the use of this product that it might break or occasionally smoke when an abnormal state occurs such as output pinVDD short (Power supply fault), output pin-GND short (Ground fault), or output-to-output-pin short (load short) . And, safety measures such as an installation of fuses are recommended because the extent of the above-mentioned damage and smoke emission will depend on the current capability of the power supply. 6. When designing your equipment, comply with the range of absolute maximum rating and the guaranteed operating conditions (operating power supply voltage and operating environment etc.). Especially, please be careful not to exceed the range of absolute maximum rating on the transient state, such as power-on, power-off and mode-switching. Otherwise, we will not be liable for any defect which may arise later in your equipment. Even when the products are used within the guaranteed values, take into the consideration of incidence of break down and failure mode, possible to occur to semiconductor products. Measures on the systems such as redundant design, arresting the spread of fire or preventing glitch are recommended in order to prevent physical injury, fire, social damages, for example, by using the products. 7. When using the LSI for new models, verify the safety including the long-term reliability for each product. 8. When the application system is designed by using this LSI, be sure to confirm notes in this book. Be sure to read the notes to descriptions and the usage notes in the book. SDG00005AEB 30 Request for your special attention and precautions in using the technical information and semiconductors described in this book (1) If any of the products or technical information described in this book is to be exported or provided to non-residents, the laws and regulations of the exporting country, especially, those with regard to security export control, must be observed. (2) The technical information described in this book is intended only to show the main characteristics and application circuit examples of the products. No license is granted in and to any intellectual property right or other right owned by Panasonic Corporation or any other company. Therefore, no responsibility is assumed by our company as to the infringement upon any such right owned by any other company which may arise as a result of the use of technical information described in this book. (3) The products described in this book are intended to be used for general applications (such as office equipment, communications equipment, measuring instruments and household appliances), or for specific applications as expressly stated in this book. Consult our sales staff in advance for information on the following applications: – Special applications (such as for airplanes, aerospace, automotive equipment, traffic signaling equipment, combustion equipment, life support systems and safety devices) in which exceptional quality and reliability are required, or if the failure or malfunction of the products may directly jeopardize life or harm the human body. It is to be understood that our company shall not be held responsible for any damage incurred as a result of or in connection with your using the products described in this book for any special application, unless our company agrees to your using the products in this book for any special application. (4) The products and product specifications described in this book are subject to change without notice for modification and/or improvement. At the final stage of your design, purchasing, or use of the products, therefore, ask for the most up-to-date Product Standards in advance to make sure that the latest specifications satisfy your requirements. (5) When designing your equipment, comply with the range of absolute maximum rating and the guaranteed operating conditions (operating power supply voltage and operating environment etc.). Especially, please be careful not to exceed the range of absolute maximum rating on the transient state, such as power-on, power-off and mode-switching. Otherwise, we will not be liable for any defect which may arise later in your equipment. Even when the products are used within the guaranteed values, take into the consideration of incidence of break down and failure mode, possible to occur to semiconductor products. Measures on the systems such as redundant design, arresting the spread of fire or preventing glitch are recommended in order to prevent physical injury, fire, social damages, for example, by using the products. (6) Comply with the instructions for use in order to prevent breakdown and characteristics change due to external factors (ESD, EOS, thermal stress and mechanical stress) at the time of handling, mounting or at customer's process. When using products for which damp-proof packing is required, satisfy the conditions, such as shelf life and the elapsed time since first opening the packages. (7) This book may be not reprinted or reproduced whether wholly or partially, without the prior written permission of our company. 20100202