AN30888B PANASONIC | Alldatasheet
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1Publication date: May 2010 SDG00005AEB DATA SHEET Part No. Package Code No. AN30888B ∗QFN016-P-0304B
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 yBattery operation : 3 V to 15 V yOutput current range : 0 A to a few Amperes depending on rating of external NMOS and mode of operation yCurrent mode control architecture yLED dimming function available by using PWM signal y30 mV / 200 mV reference voltage yLow standby current yConfigurable as either Boost/Buck-Boost/ Buck mode converter yBuilt-in various protection circuit : Under voltage lock out Over voltage protection Soft start function Applications yLED lighting module yLED lantern applications yWhite LED backlighting for LCD panel yWhite LED flash light driving applications yGeneral LED back lighting Package y16 pin Plastic Quad Flat Non-leaded Package (QFN Type) Type yBi–CMOS IC
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. Application Circuit Example (Block Diagram) y Boost Mode OVP GNDP VIN L D RCS VOUT ILED GND ENB SW CS EN UVLO PWM 3.65 V VREG 1.262 V VFB_SEL IPK CONTROL BGR VREG Reference voltage 1 μF 2.2 μF VFB VIN
Application Circuit Example (Block Diagram) (continued) y Buck-Boost Mode OVP GNDP VIN L D RCS VOUT ILED VFB IPK 2.2 μF GND ENB SW CS EN UVLO PWM 3.65 V VREG 1.262 V VFB_SEL CONTROL BGR VREG Reference voltage 1 μF VIN 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.
Application Circuit Example (Block Diagram) (continued) y Buck Mode OVP GNDP VIN GND ENB SW CS EN UVLO PWM 3.65 V VREG 1.262 V VFB_SEL CONTROL BGR VREG Reference voltage 1 μF RCS VFB IPK L D VOUT ILED 2.2 μF VIN 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.
Pin Descriptions ——N.C.16 Standby On/Off ControlInputENB12 ——N.C.11 PWM Dimming ControlInputPWM10 External NMOS Transistor Gate DriveOutputSW9 ——N.C.8 Power GroundGroundGNDP7 Over Voltage Protection input pin for Boost mode; Connect to GND for Buck modeInputOVP6 GroundGroundGND15 Regulator OutputOutputVREG14 ——N.C.13 ——N.C.5 Current SenseInputCS4 ——N.C.3 Feedback voltage selectInputVFB_SEL2 Power Supply of ICPower SupplyVIN1 DescriptionTypePin namePin No.
*3°C–25 to +85ToprOperating ambient temperature4 —A—IGNDGND pin current2 *2mW100PDPower dissipation3 NotesUnitRatingSymbolParameterA No. *3°C–55 to +125TstgStorage temperature5 *1V15.5VDDSupply voltage1 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 T a = 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 temp erature, and storage temperature, all ratings are for Ta = 25°C. 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. Operating Supply Voltage Range *1V3.0 to 12VIN1 Supply voltage range (Boost Mode/Buck-Boost Mode) *1V3.0 to 15VIN2Supply voltage range (Buck Mode) *1V3.0 to 15VINSupply voltage range NotesUnitRangeSymbolParameter Note) *1 : The values under the condition not exceeding the above absolute maximum ratings and the power dissipation. Absolute Maximum Ratings
*1V–0.3 to VINENB12 *2V–0.3 to 4.3VREG14 *2V–0.3 to 5.5PWM10 *2V–0.3 to VREGSW9 *2V–0.3 to VREGOVP6 *2V–0.3 to VREGCS4 —V–0.3 to 5.5VFB_SEL2 *1V–0.3 to 15VIN1 NoteUnitRatingPin namePin No. 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. Notes) *1 : V IN must not exceed 15 V. *2 : VREG must not exceed 4.3 V.
Under Voltage Lock Out (UVLO) —V2.32.11.9VIN Falling SW OFF; VREG =N o l o a dVUVLOONUnder Voltage protection on value12 —V0.50.30.1 VIN Rising SW ON – VIN Falling SW OFF; VREG =N o l o a d VUVLOHYSUnder voltage protection Hysteresis13 —V0.2—–0.2SW output Low logic; MOSFET OFF conditionVSWLSW Low Output Logic11 Input Pin Current Consumption —μA25——ENB = 6 VIENBEnable Pin Current9 —mA1——ENB = VIN No load conditionICCOperating Quiescent Current2 —VVREG +0.2—0.7 × VREG SW output High logic; MOSFET ON conditionVSWHSW High Output Logic10 —V0.3 × VREG —0—VVFBSELLVFB_SEL Low Input Logic6 —V5—0.7 × VREG —VVFBSELHVFB_SEL High Input Logic5 —V0.3 × VREG —0—VPWMLPWM Low input Logic8 —μA10——ENB = 0 VISTBStandby Current1 —V5—0.7 × VREG —VPWMHPWM High input Logic7 —V0.3—0—VENBLENB Low Input Logic4 Output Driver ENABLE (ENB), VFB_SEL and PWM Control Function —VVIN—3—VENBHENB High Input Logic3 Circuit Current Consumption Limits Typ Unit Max Notes Min ConditionsSymbolParameterB No. Electrical Characteristics at VIN = 6 V, ENB = 6 V, PWM = VREG Note) Ta = 25°C±2°C unless otherwise specified.
—mV403224 VFB_SEL = Low OVP = 0 V (Buck mode) V VFB2VFB Reference Voltage 2 —mV208202196 VFB_SEL = High OVP = 0 V (Buck mode) V VFB1VFB Reference Voltage 1 Reference Voltage Control —V3.853.653.45 4V ≤ VIN ≤ 15 V No Load Condition, CVREG = 1 μF VREGVREG Output Voltage 19 —%—90— VIN =6V 1 LED of VF =3 . 7V ILED = 400 mA VFB_SEL = High OVP = 0 V (Buck mode) EffEfficiency20 Regulator Voltage (VREG) —MHz1.5———F MaxMaximum Operating Frequency —μs210.5Fix off time at SW pinTOFFDriver Off Time17 Output Driver —V242118R1 = 470 kΩ, R2 = 30 kΩVOVP Over Voltage Protection Threshold 16 Efficiency Over Voltage Protection (Boost Mode Only) Reference values Typ Unit Max Notes Min ConditionsSymbolParameterB No. 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.
Control Pin Mode Table Note) See parameters B No. 3, 4, 5, 6, 7 and 8 in the Electrical Characteristics for control voltage ranges. When PWM is not used, the pin is left floatingPWM ONPWM OFFPWM ON/OFF10 Standby / Operating mode controlOPERATINGSTANDBYENB ON/OFF12 Pin voltage VFB = 202 mV High Feedback voltage selectionVFB = 32 mVVFB_SEL ON/OFF2 Remarks Low DescriptionPin No.
ENABLE (ENB), VFB_SEL and PWM Control Function Circuit Current Consumption SwitchOutputInput ParameterC No. Standby current consumption4 ENB = 0 V PWM = 0 V VFB_SEL = 0 V OVP = 0 V CS = 0 V SW = Hi-Z Standby Current1 Current consumption4 ENB = V IN PWM = 0 V VFB_SEL = 0 V OVP = 0 V CS = 0 V SW = Hi-Z Operating Quiescent Current2 Output DC voltage16 ENB = 0.30 V PWM = Hi-Z VFB_SEL = 3.65 V OVP = 0 V CS = 0 V SW = Hi-Z ENB High Input Logic3 Output DC voltage16 ENB = 3.0 V PWM = Hi-Z VFB_SEL = 3.65 V OVP = 0 V CS = 0 V SW = Hi-Z ENB Low Input Logic4 Output DC voltage / 1M H z11 ENB = V IN PWM = Hi-Z VFB_SEL = 0.70× VREG OVP = 0 V CS = 100 mV SW = Hi-Z VFB_SEL High Input Logic5 Output DC voltage / 1M H z11 ENB = V IN PWM = Hi-Z VFB_SEL = 0.30 × VREG OVP = 0 V CS = 100 mV SW = Hi-Z VFB_SEL Low Input Logic6 Output DC voltage / 1M H z11 ENB = V IN PWM = 0.70 × VREG VFB_SEL = 3.65 V OVP = 0 V CS = 0 V SW = Hi-Z PWM High input Logic7 Pin No. ConditionsConditionsPin No. Electrical Characteristics Test Procedures
Electrical Characteristics Test Procedures (continued) 222252Output DC voltage / 1M H z11 ENB = VIN PWM = 0 V VFB_SEL = 3.65 V OVP = 0 V CS = 0 V SW = 0 A SW Low Output Logic11 Output Driver Input Pin Current Consumption 222222Output DC voltage / 1M H z11 ENB = V IN PWM = 3.65 V VFB_SEL = 3.65 V OVP = 0 V CS = 0 V SW = 0 A SW High Output Logic10 SwitchOutputInput ParameterC No. Output DC voltage / 1M H z11 ENB = V IN PWM = 0.30 × VREG VFB_SEL = 3.65 V OVP = 0 V CS = 0 V SW = Hi-Z PWM Low input Logic8 Current Consumption14 ENB = V IN PWM = Hi-Z VFB_SEL = 0 V OVP = 0 V CS = 0 V SW = Hi-Z Enable Pin Current9 Pin No. ConditionsConditionsPin No.
Electrical Characteristics Test Procedures (continued) 122212Output DC voltage / 1M H z11 ENB = VIN PWM = Hi-Z VFB_SEL = 3.65 V OVP = 0 V CS = 0 V SW = Hi-Z Under voltage protection Hysteresis13 122212Output DC voltage / 1M H z11 ENB = V IN PWM = Hi-Z VFB_SEL = 3.65 V OVP = 0 V CS = 0 V SW = Hi-Z Under voltage protection on value12 Under voltage Lock Out (UVLO) SwitchOutputInput ParameterC No. S5 S6S1 S2 S3 S4Pin No. ConditionsConditionsPin No.
No connection———5 CS Current Sense Pin Z : Hi-ZDC (0 V to 250 mV)4 DC (0 V to 5 V) DC (3 V to 15 V) Waveform and voltage VFB_SEL Feedback voltage select pin Z : Hi-Z2 No connection——3 VIN Power Supply of IC Z : Low—1 Impedance DescriptionInternal circuitPin No. 200VFB_SEL VREG 500CS VREG Technical Data yI/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.
Z : 170 kΩPulse (0 V to 5 V)10 No connection———11 SW External NMOS Transistor Gate Driving Pulse Z : Hi-ZPulse (0 V to 3.65 V)9 GNDP DC (0 V to 1.26 V) Waveform and voltage Power Ground——7 No connection——8 OVP Over Voltage Protection input pin for Boost and Buck-Boost mode Connect to GND for Buck mode Z : Hi-Z6 Impedance DescriptionInternal circuitPin No. OVP VREG SW VREG 3kPWM 167k VREG VREG Technical Data (continued) yI/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.
Signal Ground——GND15 No connection———16 DC (Typ. 3.65 V) DC (3 V to 15 V) Waveform and voltage No connection——13 VREG Regulator Output Pin Z : Hi-Z14 ENB Standby On/Off Control Pin Z : 402 kΩ12 Impedance DescriptionInternal circuitPin No. ENB 20k200k 200k VREG VIN 550 550 550 Technical Data (continued) yI/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.
(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 R CS 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. )NLEDs*VFVIN(Vout−−−= -- )*(NLEDsVFVINVout−= Technical Data (continued) yFunctions and properties descriptions
(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: VIN : Battery or Input power supply voltage VF : LED forward drop voltage NLEDs : Number of LEDs stacked in series VD : 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. )NLEDs*VFVIN(Vout−−−= -- )*(NLEDsVFVINVout−= Technical Data (continued) yFunctions 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 ; V IN =6V ) VFB = 50 mV (When VFB_SEL = Low ; V IN =6V ) VFB = 198.3 mV (When VFB_SEL = Low ; V IN =3V ) VFB = 88 mV (When VFB_SEL = Low ; V IN =3V ) For Buck mode : VFB = 202 mV (When VFB_SEL = High, for all V IN level) VFB = 32 mV (When VFB_SEL = Low, for all V IN 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. Technical Data (continued) yFunctions and properties descriptions (continued)
(5) Feedback voltage VFB at CS pin (continued) 32202N.AN.A15 VFB (mV) VFB_SEL =L o w 202 202 202 202 202 202 202 202 202 202 202 202 VFB (mV) VFB_SEL = High Buck mode N.AN.A14 N.AN.A13 26.359.012 28.364.011 31.070.010 34.077.39 38.086.38 43.098.37 50.0116.06 57.7132.35 71.0161.04 88.0198.33 VFB (mV)VFB (mV) VIN (V) VFB_SEL =L o w VFB_SEL = High Boost mode/ Buck-Boost mode Technical Data (continued) yFunctions and properties descriptions (continued) BOOST MODE: VCS Voltage vs VIN 0.0 20.0 40.0 60.0 80.0 100.0 120.0 140.0 160.0 180.0 200.0 220.0 3579 1 1 VIN(V) VCS(mV) VFB_SEL="H" VFB_SEL="L" BUCK MODE: VCS Voltage vs VIN 0.0 20.0 40.0 60.0 80.0 100.0 120.0 140.0 160.0 180.0 200.0 220.0 3 5 7 9 11 13 15 VIN(V) VCS(mV) VFB_SEL="H" VFB_SEL="L"
(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 I PK, 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 0.3 × IIN (VIN – VOUT) × TOFF 0.3 × ILED 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. Technical Data (continued) yFunctions 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 TOFF =T OFF 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 IPK 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 =6V , VOUT =1 0V , ILED = 500 mA, TOFF =1 μs, L = 16 μH, VD = 0.4 V, VFB =0 . 1V @ VIN =6V (10 – 6) × 1μ 2 × 16μ 0.1 From Eq[8] : R CS = ———— = 100.8 m Ω 0.9917 Technical Data (continued) yFunctions 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 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 IPK 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 =1 2V , VOUT =2V , ILED = 500 mA, TOFF =1 μs, L = 66 μH, VFB =0 . 2V (12 – 2) × 1μ 2 × 66μ 0.2 From Eq[10] : R CS = ———— = 348 m Ω 0.575 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 R CS 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 Technical Data (continued) yFunctions 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)
V 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. Technical Data (continued) yFunctions 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. I 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. Technical Data (continued) yFunctions 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. (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. 66.3312.0 VIN (V) 69.9110.0 68.9010.5 67.9711.0 71.789.0 70.839.5 67.0911.5 72.898.5 73.928.0 75.197.5 76.257.0 77.386.5 78.406.0 79.795.5 81.995.0 83.584.5 85.274.0 87.093.5 88.733.0 Duty Limit (%) Boost/Buck-boost mode Technical Data (continued) yFunctions and properties descriptions (continued)
Technical Data (continued) yPD ⎯ Ta diagram
y Special attention and precaution in using 1. This IC is intended to be used for gene ral 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 be fore applying power, otherwise damage might happen due to problems such as a solder- bridge 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 pin- VDD 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 safe ty 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. Usage Notes
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 im- provement. 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