High-Voltage, 350mA LED Driver with Analog and PWM Dimming Control

Transcription

1 19-589; Rev ; 7/6 General Description The current regulator operates from a 5.5V to 4V input voltage range and delivers 35mA to 35mA to one or more strings of high-brightness (HB ). The output current of the is set by using an external current-sense resistor in series with the. A dual-mode pin and on-board 2Hz ramp generator allow PWM dimming with an analog or PWM input signal. The analog control signal at dimming input allows for a theater-dimming effect to be implemented. Fast turn-on and turn-off times ensure a wide-range PWM operation, while wave-shaping circuitry minimizes EMI. The differential current-sense input increases LED current accuracy and noise immunity. The is well suited for applications requiring high-voltage input and is able to withstand automotive load-dump events up to 45V. An on-board pass element minimizes external components while providing 3% 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, 2-pin TQFN package and is specified over the automotive -4 C to +125 C temperature range. Applications Automotive Interior: Map, Dome, and Courtesy Lighting Automotive Exterior: Rear Combination Light (RCL) Daytime Running Light (DRL) Adaptive Front Light Warning Lights for Emergency Vehicles Navigation and Marine Indicators Signage, Canopies, and Beacons Features Flexible Dimming Control, Analog or PWM Control Signal for PWM and Theater Dimming 2Hz On-Board Ramp Generator Sinks to External PWM Signal (Up to 2kHz) 5.5V to 4V Operating Range 35mA to 35mA Adjustable LED Current 3% LED Current Accuracy High-Voltage (Up to 4V) Pin Integrated Pass Element with Low-Dropout Voltage (.5V typ) Additional +5V On-Board Regulator with 2mA Capability Differential LED Current Sense Low 2mV Current-Sense Reference Reduces Power Losses Wave-Shaped Edges Minimize EMI During PWM Dimming Output Short-Circuit and Thermal-Shutdown Protection Available in Small, Thermally Enhanced, 5mm x 5mm, 2-Pin TQFN Package -4 C to +125 C Operating Temperature Range PART Ordering Information TEMP RANGE +Denotes lead-free package. *EP = Exposed pad. P- PACKAGE Pin Configuration appears at end of data sheet. PKG CODE ATP+ -4 C to +125 C 2 TQFN-EP* T255M-5 Simplified Diagrams +5.5V TO +4V ILED +5.5V TO +4V ILED.1μF +5V REG.1μF.1μF +5V REG.1μF RSSE PWM MG RSSE ANALOG CONTROL PWM MG PWM CONTROL MG 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 to...-.3v to +45V,, to...-.3v to (V +.3V) Slew Rate (2V < V < 45V)...25mV/µs, to...-.3v to +6V to...-.3v to +.3V Short Circuited to Duration (at V < +16V)...1hour Maximum Current Into Any Pin (except and )...±2mA Continuous Power Dissipation (T A = +7 C) 2-Pin TQFN (derate 34.5mW/ C above +7 C) mW Operating Temperature Range...-4 C to +125 C Junction Temperature C Storage Temperature Range C to +15 C Lead Temperature (soldering, 1s)...+3 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 =.1µF, I =, =, R SSE =.56Ω (see the Typical Operating Circuit), V = 4V, T A = T J = -4 C to +125 C, unless otherwise noted. Typical values are at T A = T J = +25 C.) (Note 1) PARAMETER SYMBOL CONDITIONS M TYP MAX UNITS Supply Voltage Range V (Note 2) V Ground Current I G I LOAD = 35mA ma Shutdown Supply Current I SHDN V.3V 12 4 µa Guaranteed Output Current I R SSE =.55Ω 35 ma Output Current Accuracy 35mA < I < 35mA, not including R SSE tolerance I = 35mA, 12V < V < 4V Dropout Voltage (Note 3) ΔV DO I = 35mA, 6.5V < V < 12V % V Output Current Slew Rate Current rising, rising to 4V 17 (External PWM Signal at ) Current falling, falling to.6v 17 ma/µs Short-Circuit Current V = V 6 ma ABLE PUT Input Current I 1 na Input-Voltage High V IH 2.8 V Input-Voltage Low V IL.6 V Enable Turn On Time t ON rising edge to 9% of 25 µs CURRT SSE (Note 4) Regulated R SSE Voltage V RSSE V SSE = V - V mv Input Current () V = 22mV +14 µa Input Current () V = 22mV -75 µa TERNAL RAMP GERATOR Internal Ramp Frequency f RAMP Hz External Sync Frequency Range f 8 2 Hz External Sync Voltage Low.4 V External Sync Voltage High 2.8 V EXTERNAL PWM MG PUT Input Current 1 µa Turn-On Time t ON After rising to 4V (Note 5) µs Turn-Off Time t OFF After falling to.6v (Note 5) µs 2

3 ELECTRICAL CHARACTERISTICS (continued) (V = V = 12V, C =.1µF, I =, =, R SSE =.56Ω (see the Typical Operating Circuit), V = 4V, T A = T J = -4 C to +125 C, unless otherwise noted. Typical values are at T A = T J = +25 C.) (Note 1) PARAMETER SYMBOL CONDITIONS M TYP MAX UNITS THERMAL PROTECTION Thermal-Shutdown Temperature T J(SHDN) +155 C Thermal-Shutdown Hysteresis 23 C +5V REGULATOR Output Voltage Regulation I 2mA V Short-Circuit Current = V (Note 6) 12 ma Note 1: All devices are 1% 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 a resistor from to. Connect R SSE =.56Ω from to. Set V = V +3V (record V as V 1 ). Reduce V until V =.97 x V 1 (record as V 2 and V 2 ). ΔV DO = V 2 - V 2. Note 4: I = ma. Note 5: t ON time includes the delay and the rise time needed for I to reach 9% of its final value. t OFF time is the time needed for I to drop below 1%. See the Typical Operating Characteristics. t ON and t OFF are tested with 13Ω from to. Note 6: Thermal shutdown does not function if the output of the 5V reference is shorted to ground. Shorting to disables the output. Typical Operating Characteristics (V = 12V, V = V, C =.1µF, I =, =, R SSE =.56Ω, connect to, V = 4V, T A = +25 C, unless otherwise noted.) PUT CURRT (ma) PUT CURRT vs. TEMPERATURE ILOAD = 35mA ILOAD = 2mA ILOAD = 1mA ILOAD = 35mA toc1 (V - V) (V) (V - V ) vs. PUT CURRT V = 12V toc2 PUT CURRT (ma) PUT CURRT vs. PUT VOLTAGE I = 35mA I = 1mA toc TEMPERATURE ( C) PUT CURRT (ma) PUT VOLTAGE (V) 3

4 Typical Operating Characteristics (continued) (V = 12V, V = V, C =.1µF, I =, =, R SSE =.56Ω, connect to, V = 4V, T A = +25 C, unless otherwise noted.) DROP VOLTAGE (V) DROP VOLTAGE vs. TEMPERATURE 1. V = 12V.9 ILOAD = 35mA TEMPERATURE ( C) toc4 SHUTDOWN CURRT (μa) V = 4V V = 12V V = 6.5V SHUTDOWN CURRT vs. TEMPERATURE V = 2V TEMPERATURE ( C) toc5 +5V REGULATOR PUT (V) V REGULATOR PUT vs. TEMPERATURE ILOAD = 1mA ILOAD = 2mA NO LOAD V = 12V TEMPERATURE ( C) toc6 +5V REGULATOR PUT (V) V REGULATOR PUT vs. V NO LOAD ILOAD = 2mA ILOAD = 1mA toc7 (V - V) (V) (V - V) vs. I ILOAD = 35mA V = 12V toc8 2Hz MED OPERATION I LOAD = 35mA V = 12V PULSED AT 2Hz (1% DUTY CYCLE) toc9 V 2V/div V I LOAD 2mA/div A V (V) I (ma) 2μs/div LED CURRT FALL TIME (EXPANDED) toc1 LED CURRT RISE TIME (EXPANDED) toc11 PULSED AT 2Hz V 2V/div PULSED AT 2Hz V 2V/div V V I LED 2mA/div I LED 2mA/div A A 2μs/div 2μs/div 4

5 Typical Operating Characteristics (continued) (V = 12V, V = V, C =.1µF, I =, =, R SSE =.56Ω, connect to, V = 4V, T A = +25 C, unless otherwise noted.) PUT CURRT DUTY CYCLE (%) PUT CURRT DUTY CYCLE vs. ANALOG VOLTAGE V = 12V toc12 I (μa) V = 16V I vs. V toc ANALOG VOLTAGE (V) V (V) Pin Description P NAME FUNCTION 1, 2 Current-Regulated Output. Connect pin 1 to pin 2. 2, 3 Input Supply. Bypass with a.1µf (min) capacitor to. Connect pin 2 to pin 3. 4, 9, 11, 18 N.C. No Connection. Leave unconnected (internal connection). 5 8, 1, 16 Ground 12, 15 +5V Regulated Output. Connect a.1µf capacitor from to. 13 Positive Input of the Internal Differential Amplifier. Connect the current-sense resistor between and to program the output current level. 14 Negative Input of the Internal Differential Amplifier. Connect the current-sense resistor between and to program the output current level. 17 Dimming Input. See the Dimming Input () section. 19 Enable Input. Drive high to enable the output and the 5V LDO. EP Exposed Pad. Connect to the ground plane for effective power dissipation. Do not use as the only ground connection. 5

6 TRIMMED BANDGAP 1.25V REGULATOR Functional Diagram I_ REG DIFFERTIAL SSE AMPLIFIER 21mV THERMAL SHUTDOWN 2Hz RAMP GERATOR MUX POR PULSE DETECTOR Detailed Description The is a high-current regulator capable of providing up to 35mA of current to one or more strings of HB. A wide operating input voltage range of 5.5V to 4V makes the ideal for automotive applications. A +5V regulated output provides up to 2mA 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 45V. 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 pass device (see the Functional Diagram). The regulation point is factory-set at (V - V ) = 198 ±6mV. 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 to ten or more HB. Dimming Input () The s dimming input functions with either an analog or PWM control signal. If the pulse detector detects three edges of a PWM signal with a frequency range between 8Hz to 2kHz, the synchronizes to external PWM input signal and pulse-widthmodulates the LED current. If an analog control signal is applied to, the compares the DC input to an internally generated 2Hz ramp to pulsewidth-modulate the LED current. The output current duty cycle is adjustable from % to 1% (.21V < V < 3.1V). Use the following formula to calculate the output current duty cycle: Duty cycle = (V -.21V) / (2.895V) (1) 6

7 The dimming feature can be used for LED brightness adjustment (see the Simplified Diagrams) and theater dimming. If an external PWM signal is used, the theaterdimming effect can be achieved by varying the PWM duty cycle. Figure 1 shows a simple circuit that implements theater dimming with a DC input signal. +5V Regulator The includes a fixed +5V output regulator that delivers up to 2mA of load current throughout the 6.5V to 4V input voltage range. Connect a.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 short-circuit conditions on the output. 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 (2) Input-Voltage Considerations For proper operation, the minimum input voltage must always be: V(M) VRSSE(MAX) + VFT(MAX) + ΔVDO(MAX) (3) where V FT(MAX) is the maximum forward voltage of all series connected and ΔVDO(MAX) is the maximum drop output voltage. The minimum operating voltage of the device is +5.5V. Two Brightness Levels for TAIL/STOP Lights Figure 2 shows two-level brightness adjustment using the with minimum external components. Set the dimming level with a resistive divider connected to. See Equation 1 for details. STOP D1 V THEATER MG SIGNAL +5V REG.1μF TAIL R1 D2 RSSE R2 R SSE Figure 1. Theater Dimming Figure 2. Two-Level Brightness Operation 7

8 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 3 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 (4) Other Applications Figure 4 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 (5) where V CESAT(MAX) is the maximum saturation voltage of the external BJT. V C1 PWM MG C2 RT R2 R1 Figure 3. LED Current Thermal Foldback Operation with an NTC Thermistor V C1 Q1 PWM MG C2 R SSE Figure 4. Increased Output Current (Amper Range) with a Single BJT 8

9 ANALOG OR PWM CONTROL SIGNAL V N.C. 16 Typical Operating Circuit C R SSE 4 N.C N.C N.C C2 Pin Configuration PROCESS: BiCMOS Chip Information TOP VIEW N.C N.C N.C. 9 N.C TH QFN 9

10 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 1

11 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. Maxim Integrated Products, 12 San Gabriel Drive, Sunnyvale, CA Maxim Integrated Products is a registered trademark of Maxim Integrated Products, Inc. Heaney