High-Voltage, 350mA, High-Brightness LED Driver with PWM Dimming and 5V Regulator

Transcription

1 ; Rev 0; 5/06 EVALUATION KIT AVAILABLE High-Voltage, 350mA, High-Brightness LED General Description The current regulator operates from a 6.5V to 40V input-voltage range and delivers up to a total of 350mA to one or more strings of high-brightness (HB ). The output current of the is adjusted by using an external current-sense resistor in series with the. A dimming input allows widerange pulsed PWM operation. Wave-shaping circuitry reduces EMI. The differential current-sense input increases noise immunity. The is well suited for applications requiring high-voltage input and is able to withstand automotive load-dump events up to 40V. An on-board pass element minimizes external components while providing ±3.5% output-current accuracy. Additional features include a 5V regulated output and short-circuit and thermal protection. The is available in a thermally enhanced, 5mm x 5mm, 16-pin TQFN package and is specified over the automotive -40 C to +125 C temperature range. Applications Automotive Interior: Map, Courtesy, and Cluster Lighting Automotive Exterior: Rear Combination Lights (RCLs) Emergency Vehicle Warning Lights Navigation and Marine Indicators General Lighting Signage, Gasoline Canopies, Beacons Pin Configuration Features +6.5V to +40V Operating Range Adjustable LED Current (35mA to 350mA) ±3.5% LED Current Accuracy High-Voltage Pin for Dimming Interface Integrated Pass Element with Low-Dropout Voltage (0.5V typ) +5V Regulated Output with 4mA Source Capability Parallel Operation for LED Current > 350mA Differential LED Current Sense Low Shutdown Supply Current (12µA typ) Low 204mV Current-Sense Reference Reduces Power Losses Wave-Shaped Edges Reduce Radiated EMI During PWM Dimming Thermal Shutdown Output Short-Circuit Protection Available in Small, Thermally Enhanced, 5mm x 5mm, 16-Pin TQFN Package -40 C to +125 C Operating Temperature Range PART Ordering Information TEMP RANGE P- PACKAGE PKG CODE ATE+ -40 C to +125 C 16 TQFN-EP* T Denotes lead-free package. *EP = Exposed pad. Simplified Diagram TOP VIEW µF +6.5V TO +40V PWM MG +5V REG 0.1µF RSSE TQFN Maxim Integrated Products 1 For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at , or visit Maxim s website at

2 ABSOLUTE MAXIMUM RATGS,,, and to v to +45V,, to v to +6V Short Circuited to Duration (at V = +16V)...60 minutes Maximum Current Into Any Pin (except and )...±20mA Continuous Power Dissipation (T A = +70 C) 16-Pin TQFN (derate 33.3mW/ C above +70 C) mW Operating Junction Temperature Range C to +125 C Junction Temperature C Storage Temperature Range C to +150 C Lead Temperature (soldering, 10s) C Stresses beyond those listed under Absolute Maximum Ratings may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability. ELECTRICAL CHARACTERISTICS (V = V = +12V, C = 0.1µF to, I = 0, V = 0V, V = +4V, connect R SSE = 0.58Ω between and (Note 1). T J = -40 C to +125 C, unless otherwise noted. Typical values are at T A = +25 C.) (Note 1) PARAMETER SYMBOL CONDITIONS M TYP MAX UNITS Supply Voltage Range V (Note 2) V Ground Current I G I LOAD = 350mA ma Shutdown Supply Current I SHDN 0.6V µa Guaranteed Output Current I R SSE = 0.55Ω 350 ma Output Current Accuracy 35mA < I < 350mA ±3.5 % Dropout Voltage (Note 3) Output Current Slew Rate VDO I = 350mA (current pulsed), 12V < V < 40V I = 350mA (current pulsed), 6.5V < V < 12V Current rising, rising to 4V 17 Current falling, falling to 0.6V Short-Circuit Current V = 0V, V = 12V ma LOGIC PUT Input Current I 100 na Input Voltage High V IH 2.8 V Input Voltage Low V IL 0.6 V Turn On Time t ON rising edge to 90% of 80 µs CURRT SSE (Note 4) Regulated R SSE Voltage V RSNS V SSE = V - V mv Voltage Range V Input Current () V = 220mV +14 µa Input Current () V = 220mV -84 µa Input Current 1 µa Input Voltage High V IH 4 V Input Voltage Low V IL 0.6 V Turn-On Time t ON After rising to 4V (Note 5) 52 µs Turn-Off Time t OFF After falling to 0.6V (Note 5) 38 µs V ma/µs 2

3 ELECTRICAL CHARACTERISTICS (continued) (V = V = +12V, C = 0.1µF to, I = 0, V = 0V, V = +4V, connect R SSE = 0.58Ω between and (Note 1). T J = -40 C to +125 C, unless otherwise noted. Typical values are at T A = +25 C.) (Note 1) PARAMETER SYMBOL CONDITIONS M TYP MAX UNITS THERMAL OVERLOAD Thermal-Shutdown Temperature +155 C Thermal-Shutdown Hysteresis 23 C +5V REGULATOR Output Voltage Regulation (Note 6) V Short-Circuit Current = 0V (Note 7) 16 ma Note 1: All devices 100% production tested at T A = +25 C. Limits over the operating temperature range are guaranteed by design. Note 2: Resistors were added from to to aid with the power dissipation during testing. Note 3: Dropout is measured as follows: Connect R O = 27Ω from to. Connect R SSE = 0.58Ω from to. Set V = +12V (record V as V 1 ). Reduce V until V = 0.97 x V 1 (record as V 2 and V 2 ). V DO = V 2 - V 2. Note 4: I = 0mA. Note 5: t ON time includes the delay and the rise time needed for I to reach 90% of its final value. t OFF time is the time needed for I to drop below 10%. See the Typical Operating Characteristics. t ON and t OFF are tested with 13Ω from to CST. Note 6: Current regulation varies with load (see the Typical Operating Characteristics). Note 7: Thermal shutdown does not function if the output of the 5V reference is shorted to ground. (V = V = +12V, T A = +25 C, unless otherwise noted.) Typical Operating Characteristics PUT CURRT (ma) PUT CURRT vs. TEMPERATURE ILOAD = 350mA ILOAD = 200mA ILOAD = 100mA ILOAD = 35mA TEMPERATURE ( C) toc01 (V - V) (V) (V - V ) vs. PUT CURRT V = 12V PUT CURRT (ma) toc02 PUT CURRT (ma) PUT CURRT vs. PUT VOLTAGE PUT VOLTAGE (V) toc03 3

4 Typical Operating Characteristics (continued) (V = V = +12V, T A = +25 C, unless otherwise noted.) DROP VOLTAGE (V) DROP VOLTAGE vs. TEMPERATURE ILOAD = 350mA TEMPERATURE ( C) toc04 SHUTDOWN CURRT (µa) SHUTDOWN CURRT vs. TEMPERATURE V = 40V V = 20V V = 12V V = 6.5V TEMPERATURE ( C) toc05 5V REGULATOR PUT (V) V REGULATOR PUT vs. TEMPERATURE ILOAD = 1mA ILOAD = 5mA NO LOAD TEMPERATURE ( C) toc06 (V - V) (V) (V - V) vs. I ILOAD = 410mA I (ma) toc07 5V REGULATOR PUT (V) V REGULATOR PUT vs. V NO LOAD LOAD = 1mA LOAD = 5mA V (V) toc08 200Hz MED OPERATION I LOAD = 350mA V = V = 12V PULSED AT 200Hz (1% DUTY CYCLE) 20µs/div toc09 V 2V/div 0V I LOAD 200mA/div 0A 200Hz MED OPERATION (EXPANDED) I LOAD = 350mA V = V = 12V PULSED AT 200Hz (50% DUTY CYCLE) toc10 V 2V/div 0V I LOAD 200mA/div 0A 200Hz MED OPERATION (EXPANDED) toc11 I LOAD = 350mA V = V = 12V PULSED AT 200Hz (50% DUTY CYCLE) V 2V/div 0V I LOAD 200mA/div 0A 20µs/div 20µs/div 4

5 Typical Operating Characteristics (continued) (V = V = +12V, T A = +25 C, unless otherwise noted.) VSNSE (mv) V SNSE vs. V toc12 I (µa) I vs. V toc V = 12V ILOAD = 350mA V (V) V (V) Pin Description P NAME FUNCTION 1, 16 Current-Regulated Output. Connect pin 1 to pin 16. 2, 3 Positive Input Supply. Bypass with a 0.1µF (min) capacitor to. Connect pin 2 to pin , 14 Not Internally Connected 9 Positive Input of the Internal Differential Amplifier. Connect the current-sense resistor between and to program the output current level. 10 Negative Input of the Internal Differential Amplifier. Connect the current-sense resistor between and to program the output current level V Regulated Output. Connect a 0.1µF capacitor from to. 12 Ground 13 Pulsed Dimming Input. Drive low to disable the output. Drive high to enable the output. Must not be left unconnected. 15 Enable Input. Drive high to enable the output. EP Exposed Pad. Connect to the ground plane for effective power dissipation. Do not use as the only ground connection. 5

6 ABLE REFERCE GERATOR REGULATOR I_ REG Functional Diagram DIFFERTIAL SSE AMPLIFIER THERMAL SHUTDOWN Detailed Description The is a high-current regulator capable of providing up to a total of 350mA of current to one or more strings of HB. A wide operating input voltage range of +6.5V to +40V makes the ideal for automotive applications. A +5V regulated output provides up to 4mA of current to power external circuitry. In addition, the features thermal and output short-circuit protection. The wide operating voltage range helps protect the against large transients such as those found in load-dump situations up to 40V. The uses a feedback loop to control the output current. The differential voltage across the sense resistor is compared to a fixed reference voltage, and the error is amplified to serve as the drive to the internal power series pass device (see the Functional Diagram). The regulation point is factory-set at (V - V ) = 203mV ±3.5%. The regulated current is user defined by the value of R SSE. The is a current controller internally optimized for driving the impedance range expected from one or more HB. +5V Regulator The includes a fixed +5V output regulator that delivers up to 4mA of load current throughout the +6.5V to +40V input voltage range. Connect a 0.1µF compensation capacitor from to ground. Shorting to ground disables the thermal shutdown. When is low, is off. stays on during PWM dimming. Thermal Protection The enters a thermal-shutdown mode in the event of overheating. This typically occurs in overload or output short-circuit conditions. If the junction temperature exceeds T J = +155 C (typ), the internal thermal-protection circuitry turns off the series pass device. The recovers from thermal-shutdown mode once the junction temperature drops by 23 C (typ). The part therefore protects itself by thermally cycling in the event of a short-circuit or overload condition. Applications Information Programming the LED Current The uses a sense resistor across and to set the LED current. The differential sense amplifier connected across R SSE provides ground-loop immunity and low-frequency noise rejection. The LED current is given by I LED = V SSE / R SSE 6

7 Input-Voltage Considerations For proper operation, the minimum input voltage must always be: V(M) VRSSE(MAX) + VFT(MAX) + VDO(MAX) where V FT(MAX) is the total forward voltage of all series connected. The minimum operating voltage of the device is +6.5V. The device operates below +6.5V; however, output current may not meet the full regulation specification (see the Typical Operating Characteristics). Low-Frequency PWM Dimming at the Output The provides pulsed or chopped current dimming input (). The other method is to connect to and to and pulse. Both methods generate a regulated-amplitude PWM current (variable duty cycle) that can provide control over the LED brightness (see Figures 1 and 2). Paralleling Multiple s to Drive One High-Power LED For applications that require more than 350mA of LED current, two or more s can be paralleled (see Figure 3). V should not exceed 4.1V. R1 V ILED V D1 R SSE R2 5 6 Figure 1. Dimming with Connected to V at a Constant Voltage and Pulsed 7 8 C3 C V D1 ILED R SSE Figure 3. Paralleling s Figure 2. Dimming with Connected to, Connected to V 7

8 Two Brightness Levels for TAIL/STOP Lights Figure 4 shows PWM dimming operation for the with an ICM7555 timer. The ICM7555 provides adjustable duty cycle using two external resistors and a capacitor. In TAIL operation, the output of the ICM7555 feeds into and lights up the. The LED s brightness depends on the duty cycle of the ICM7555. When V STOP is present, is pulled up to V STOP. The PWM dimming operation is disabled and the light up to full brightness. See the ICM7555 data sheet for formulas to calculate the dimming frequency and the duty cycle. LED Current Thermal Foldback With a minimum number of external components, the provides LED current thermal foldback using a negative temperature coefficient (NTC) thermistor. Figure 5 shows a thermistor connected to and the of the. As the temperature increases, the voltage drop across R2 increases causing the LED current to decrease. I LED = [V SSE - [R2 / (R2 + RT)] x ] / R1 D1 STOP D2 TAIL R1 R2 D3 +5V REG D4 DIS R3 ICM7555 R SSE TH TRG C3 Figure 4. PWM Dimming Operation with ICM7555 Timer V PWM MG RT R2 R1 Figure 5. LED Current Thermal Foldback with an NTC Thermistor 8

9 Other Applications The application circuit in Figure 6 implements a twolevel brightness current for TAIL/STOP lights. In TAIL operation, Q1 is off and the R1 sets the output current. In STOP operation, Q1 turns on and the output current is set by a parallel combination of R1 and R2. STOP Figure 7 shows an application circuit with the using a single BJT to provide high output current. For proper operation: V (M) > V CESAT(MAX) + V FT(MAX) + V RSSE where V CESAT(MAX) is the maximum saturation voltage of the external BJT. TAIL R2 R1 Q1 Figure 6. Two Brightness Level with Current Level Switch for Tail/Stop Lights V Q1 PWM MG R SSE Figure 7. Increased LED Current (Amper Range) with a Single BJT 9

10 Multichannel HB LED Driver Figure 8 shows an array of s with independent control. The MAX5094C, a current-mode PWM controller, provides the input power to each LED driver preregulated voltage to multiple drivers. V L1 D1 CREF CCOMP REF COMP MAX5094C VCC C3 Q1 C4 R3 U2 U4 U3 RCOMP C6 C7 0 1 C8 C9 FB R5 R7 R6 CT/RT CS R4 CT R2 Figure 8. Multichannel HB LED Driver for LCD Backlight V Typical Operating Circuit PROCESS: BiCMOS Chip Information V D1 R SSE

11 Package Information (The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information go to QFN TH.EPS 11

12 Package Information (continued) (The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information go to Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are implied. Maxim reserves the right to change the circuitry and specifications without notice at any time. 12 Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA Maxim Integrated Products is a registered trademark of Maxim Integrated Products, Inc. Heaney