FEATURES OUT OE GND ISET VDD OUT OE GND ISET VDD TO-220-5L. (Top View)

Transcription

1 GENERAL DESCRIPTION The LSP7706 is a high voltage, low dropout current regulator for high power LED lighting. The LSP can handle the maximum output current up to 1.1Amp. The output current can also be varied by an external resistor. The output sink current could be switched off via OE pin. And the OE pin can also be used to control PWM dimming function. TO-263 green package is available to enhance the power dissipation of the driver. The LSP7706 also features with build-in thermal protection to prevent the chip from over heat damage. The adequate thermal pad in PCB area is required to control the junction temperature below 125 C. FEATURES 0.8V Output Drop-out Voltage at 1.1Amp. 1.1Amp. Maximum Output Current. Output Current Controlled by External Resistor. 3us Fast Response Output Stage Enable Control. Output Pin Sustain Voltage Up To 75V. Supply Voltage Range 5V~50V. Green TO-263-5L package. TYPICAL APPLICATIONS High Power LED Driver RGB Full Color Power LED driver LCD Monitor/TV LED Backlight Driver LED Lighting LED Street Lamp / Table Lamp PIN ASSIGNMENT OUT OE GND ISET VDD OUT OE GND ISET VDD TO-263-5L (Top View) TO-252-5L (Top View) OUT OE GND ISET VDD TO-220-5L (Top View) PIN DESCRIPTION Pin Number Pin Name Pin Function 1 VDD Power supply. 2 I SET 3 GND Ground. 4 OE Output current set input. Connect a resistor from I SET to GND to set the LED bias current. Output stage enable control pin. High enable the OUT pin. It can be left floating for normally on. The pin can also be used for PWM dimming function. 5 OUT Output pin. Sink current is decided by the current on R SET connected to I SET. 1.2V I OUT = I SET 500 = 500 R SET Thermal Pad Ground. 1/1

2 TYPICAL APPLICATION CIRCUIT ABSOLUTE MAXIMUM RATINGS Parameters Rating Unit Input Voltage, V DD 50 V Output Pin Sustain Voltage, V OUT 75 V Enable Voltage, V OE 13.2 V Maximum Operating Junction Temperature, T J 150 C Storage Temperature Range -65 to 150 C Lead Temperature (soldering, 10 seconds) 260 C Note: Exceeding these ratings could cause damage to the device. All voltages are with respect to Ground. Currents are positive into, negative out of the specified terminal. THERMAL IMPEDIENCE TO-263, TO-220 Package: Thermal Resistance-Junction to Tab, θ JT 3 C /W Thermal Resistance-Junction to Ambient, θ JA 45 C /W TO-252 Package: Thermal Resistance-Junction to Tab, θ JT 7 C /W Thermal Resistance-Junction to Ambient, θ JA 80 C /W Junction Temperature Calculation: T J = T A + (P D θ JA). The θ JA numbers are guidelines for the thermal performance of the device/pc-board system. Connect the thermal pad to ground using a large pad or ground plane for better heat dissipation. All of the above assume no ambient airflow. 2/2

3 RECOMMENDED OPERATION Parameter Symbol Min Typ Max Unit Supply Voltage V DD 5 50 V Output Sink Current I OUT A Operating Free-Air Temperature Range T A C Operating Junction Temperature T J +125 C ELECTRICAL CHARACTERISTICS V DD =24V, T A =25 C (Unless otherwise noted) Parameter Condition Min Typ Max Unit Output Current V OUT =0.5V, R SET = V OUT =0.7V, R SET = ma Output Current Deviation V OUT =0.5V, R SET =800 V OUT =0.7V, R SET = % ISET Pin Current Range ma Maximum Output Current V OUT =0.8V, R SET = ma R SET =800, I OUT =750mA 0.5 Output Drop-out Voltage Note 1 R SET =600, I OUT =1A 0.7 V Load Regulation I OUT =750mA, V OUT =0.5V to 3V 8 ma Line Regulation I OUT =750mA, V OUT =0.5V, V DD = 5V to 50V, 6 ma Thermal Shut-down Junction Temperature Hysteresis Low Input Voltage V High Input Voltage 2 Min{V DD, 12} V Low Input Current µa High Input Current µa Output Enable Delay Time Output Disable Delay Time OE from Low to High, V OUT =0.5V, I OUT =750mA, 50% OE from High to Low, V OUT =0.5V, I OUT =750mA, 50% 5 µs 5 µs Supply Current Consumption 7 ma Note1: Output dropout voltage: 90% x I V OUT =0.8V 3/3

4 FUNCTIONAL BLOCK DIAGRAM VDD OE OUT Band-gap Reference V REF Control Circuit FB A711 ISET GND TYPICAL CHARACTERISTICS Supply Current vs. Supply Voltage ISET Voltage vs. Junction Temperature Supply Current (ma) I OUT =1100mA I OUT =900mA I OUT =700mA I OUT =500mA I OUT =330mA V DROP =0.8V T A =25 C ISET Voltage (V) V DD =24V Supply Voltage (V) Junction Temperature ( C) Output Current vs. Supply Voltage Output Current vs. Dropout Voltage I OUT =1100mA V DD =24V T A =25 C I OUT =1100mA Output Current (ma) V DROP =1V T A =25 C I OUT =900mA I OUT =700mA I OUT =500mA I OUT =330mA Output Current (ma) I OUT =900mA I OUT =700mA I OUT =500mA I OUT =330mA Supply Voltage (V) Dropout Voltage (V) 4/4

5 R SET vs. Output Current R SET (K ) V DROP =1V T A =25 C Output Current (ma) FUNCTION DESCRIPTION LSP7706 is a high voltage, high current, and low dropout current regulator for maximum output current up to 1.1A. The OE pin is used for enabling/disabling the output stage of the chip. The current could be linearly adjusted through external resister, R SET, connected to I SET pin, or by PWM control via OE pin. Although the absolute maximum rating of OUT pin 75V, the dropout voltage between OUT pin and GND pin should not be too large when current is sinking because of the heat dissipation capability of the package and PCB layout. 1. Setting LED Current An external resistor R SET connected to I SET pin sets the sink current of OUT pin. The value of R SET is calculated by the following formula: 1.2V IOUT = I SET 500 = 500 (ma) R ( KΩ) 2. PWM Dimming Control SET LSP7706 provides PWM dimming control function through OE pin. Basically, by changing the duty cycle of the PWM control signal, the ratio of LED ON-time to OFF-time can be changed. Consequently, larger duty cycle results in larger average current for driving LED and thus higher luminance. Ideally, the average LED driving current is in linear proportion to the duty cycle of the PWM control signal in spite of the frequency. However, due to the inherent propagation delay of the chip and the rising/falling time of the driving current, the deviation of the actual current from theoretical value will become larger when the PWM frequency gets higher. That is, if the PWM frequency exceeds certain recommended value, the effect of the fixed propagation delay and the rising/falling time of LED current on the linear relationship between the duty cycle and the average current will become more apparent. On the other hand, if the PWM frequency is too low, the flicker will become observable. Therefore, it is important to choose a suitable frequency for the PWM signal. Please refer to the following timing chart & table for the limitation of maximum dimming frequency. It is determined by the minimum duty ratio, D MIN, and the minimum LED ON time, t ON,MIN. The maximum dimming frequency, f PWM, can be calculated by the following formula: 1 ton, MIN = f D PWM, MAX MIN Where, duty ratio is defined as: D = t ON ton + t OFF 5/5

6 t ON t OFF OE VOE 50%*VOE t plh t phl t R t F I LED 50%*IOUT IOUT Characteristic Symbol Min Typ Max Unit LED ON Period (OE Pin Control Signal) t ON 5 us LED OFF Period (OE Pin Control Signal) t OFF 5 us Propagation Delay Time (Output Current from L to H ) t plh us Propagation Delay Time (Output Current from H to L ) t phl us Output Current Rising Time (Rising from 10% to 90%) t R us Output Current falling Time (Falling from 90% to 10%) t F us 3. DC Voltage Input Any DC voltage level between 5V to 50V could be adopted as power source VDD for typical application of LSP7706 as long as VDD is larger than the total forward voltage drop of the LED string by the minimum dropout voltage (between OUT pin and GND pin) needed for the expecting current. If 50V ~ 100V voltage level is adopted as power source to positive end of the LED string, one Zener shunt regulator could be used to provide appropriate voltage (lower than 50V) to VDD pin. The supply voltage to VDD pin and LED+ end could also be separated. Note that, heat-sink area on PCB is required if the dropout voltage between OUT pin and GND pin is too large. Please refer to the Thermal Consideration section. 6/6

7 4. Application for LED Lighting LSP7706 could coordinate with any type of DC-to-DC converter through feedback path to realize LED lighting module. The number of LEDs in the string is variable even with certain fixed power source since the output voltage of the DC-to-DC converter could be modulated according to feedback signal. In the following figure, D FB is used to feed the dropout voltage of OUT pin of the LSP7706 back to DC/DC converter; and R FB is the pull-high resistor for D FB. 5. AC Voltage Input LSP7706 could work with any kind of well-developed switch-mode power supply system. Simply cut off the internal feedback path of the power supply system and then feed the signal from LSP7706 back to the power supply system instead. 7/7

8 6. Output Capacitor C O If the LED string and LSP7706 is located in separate PCBs, or the length of the routing path L1>10cm or L2>3cm, the output capacitor C O should be added. Typically, capacitance of 0.1uF ~ 1uF is recommended and 1uF is needed when L2 is much longer than 3cm. The output capacitor C O may be neglected under certain condition. If the LED string and LSP7706 are located in the same PCB, and the length of the routing path L1<10cm & L2<3cm, the output capacitor C O can be neglected. 8/8

9 THERMAL IMPEDIENCE The Maximum Power Dissipation on Current Regulator P D(MAX) = V OUT(MAX) I OUT(NOM) + V IN(MAX) I DD V OUT(MAX) = the maximum voltage on output pin; I OUT(NOM) = the nominal output current; I DD = the quiescent current the regulator consumes at I OUT(NOM) ; V IN(MAX) = the maximum input voltage. Thermal Consideration The LSP7706 has internal power and thermal limiting circuitry designed to protect the device under overload conditions. However, maximum junction temperature ratings should not be exceeded under continuous normal load conditions. The thermal protection circuit of LSP7706 prevents the device from damage due to excessive power dissipation. When the device junction temperature rises to approximately 160 C, the regulator will be turned off. When power consumption is over about 1.22W (TO-263 and TO-220 package, at T A =70 C), additional heat sink is required to control the junction temperature below 125 C. The junction temperature is: T J = P D ( JT + TS + SA ) + T A P D : Dissipated power. JT : Thermal resistance from the junction to the mounting tab of the package. For TO-263 package, JT = 3.0 oc /W. TS : Thermal resistance through the interface between the IC and the surface on which it is mounted. (typically, TS < 1.0 C /W) SA : Thermal resistance from the mounting surface to ambient (thermal resistance of the heat sink). If PC Board copper is going to be used as a heat sink, below table can be used to determine the appropriate size of copper foil required. For multi-layered PCB, these layers can also be used as a heat sink. They can be connected with several through-hole vias. PCB SA ( C /W) PCB heat sink size (mm 2 ) Recommended figure of PCB area used as a heat sink. Thermal-pad of TO-263 Through hole vias OUT OE GND ISET VDD 9/9

10 ORDERING INFORMATION LSP7706X X X X Package: D: TO252 K: TO263 T: TO220 Output Voltage: Blank: Adj Packing: A: Tape & Real Temperature Grade: d: -40~85 MARKING INFORMATION TO263-5L TO252-5L 10/10

11 PACKAGE INFORMATION 5-Pin Surface Mount TO-263 A I C D INCHES MILLIMETERS MIN TYP MAX MIN TYP MAX A B B C D K E M N F G I L K G F E L M 7 7 N Pin Plastic TO-220 B S C INCHES MILLIMETERS MIN TYP MAX MIN TYP MAX F T A A B C D F G J K K N TYP 6.80 TYP R S G N D R J T /11

12 TO-252-5L Symbol Dimensions in Millimeters Dimensions in Inches MIN MAX MIN MAX A A B C c D D E E TYP TYP e TYP TYP L L L V REF REF UPDATE HISTORY Date Version Description July 20, New generation 12/12