MP24892DJ-LF-P

MP24892 Step Down White LED Driver with Wide 6V–45V Input Voltage The Future of Analog IC Technology DESCRIPTION FEATURES The MP24892 is a high-efficiency step-down converter that functions in continuous current mode to drive high-brightness LED. It can take a wide input voltage range of 6V–45V.           The MP24892 employs a hysteretic control architecture to regulate a high-accuracy LED current, which is measured through an external high-side current-sensing resistor. Moreover, this control scheme provides optimal circuit stabilization and a very quick response time without loop compensation. Its low 202mV average feedback voltage reduces power loss and improves the converter efficiency. Wide 6V-to-45V Input Range 1A Output Current High Efficiency (>95%) Hysteresis Control PWM & Analog Dimming 1000:1 PWM Dimming Resolution Thermal Shutdown Inherent Open LED Protection Short LED Protection Available in a TSOT23-5 Package APPLICATIONS      The MP24892 implements PWM and analog dimming together through the DIM pin. The MP24892 includes thermal overload protection that prevents damage in the event of an output overload. Low-Voltage Halogen Replacement Low-Voltage General Illumination Automotive/Decorative LED Lighting Signs/Emergency Lighting LED Backlighting All MPS parts are lead-free and adhere to the RoHS directive. For MPS green status, please visit MPS website under the Products, Quality Assurance page. The MP24892 is available in a small TSOT23-5 package. “MPS” and “The Future of Analog IC Technology” are Registered Trademarks of Monolithic Power Systems, Inc. TYPICAL APPLICATION D1 VIN 45 RSENSE CIN IN RS L1 MP24892 EN/DIM GND MP24892 Rev. 1.0 11/3/2011 SW www.MonolithicPower.com MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2011 MPS. All Rights Reserved. 1 MP24892 – STEP DOWN WLED DRIVER WITH WIDE 6V–45V INPUT VOLTAGE ORDERING INFORMATION Part Number Package TSOT23-5 MP24892DJ* Top Marking ABHY * For Tape & Reel, add suffix –Z (e.g. MP24892DJ–Z); PACKAGE REFERENCE TSOT23-5 (4) ABSOLUTE MAXIMUM RATINGS (1) Thermal Resistance VIN, VSW .........................................-0.3V to +50V VRS .................................................. VIN-5V to VIN All Other Pins ...............................-0.3V to +6.3V Continuous Power Dissipation (TA = +25°C) (2) TSOT23-5 ................................................ 1.25W Junction Temperature ...............................150C Lead Temperature ....................................260C Storage Temperature ............... -65C to +150C TSOT23-5 ............................. 100 ..... 55 ... C/W Recommended Operating Conditions (3) Supply Voltage VIN .............................. 6V to 45V Maximum Junction Temp. (TJ) -40°C to +125°C MP24892 Rev. 1.0 11/3/2011 θJA θJC Notes: 1) Exceeding these ratings may damage the device. 2) The maximum allowable power dissipation is a function of the maximum junction temperature TJ(MAX), the junction-toambient thermal resistance θJA, and the ambient temperature TA. The maximum allowable continuous power dissipation at any ambient temperature is calculated by PD(MAX)=(TJ(MAX)TA)/ θJA. Exceeding the maximum allowable power dissipation will cause excessive die temperature, and the regulator will go into thermal shutdown. Internal thermal shutdown circuitry protects the device from permanent damage. 3) The device is not guaranteed to function outside of its operation conditions. 4) Measured on JESD51-7, 4-layer PCB. www.MonolithicPower.com MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2011 MPS. All Rights Reserved. 2 MP24892 – STEP DOWN WLED DRIVER WITH WIDE 6V–45V INPUT VOLTAGE ELECTRICAL CHARACTERISTICS VIN = 24V, TA = +25C, unless otherwise noted. Parameter Input Voltage Shutdown Supply Current Quiescent Supply Current Internal Reference Voltage Symbol Condition VIN ISD IQ No Switching IREF Min 6 Feedback Reference Voltage (with respect to VIN) VIN-VRS 192 Feedback Reference Voltage Hysterisis EN/DIM Max. Dimming Voltage EN/DIM Mim. Dimming Voltage EN/DIM Enable High Voltage EN/DIM Enable Hysteresis EN/DIM Pull-Up Resistor Recommended PWM Dimming Frequency Switch On Resistance Minimum On Time Minimum Off Time Recommended Maximum Operating Frequency Recommended Duty Cycle Range at fMAX Start-Up Time MP24892 Rev. 1.0 11/3/2011 VEN/DIM = 1.28V Typ Units V µA mA V 212 mV 1.275 VFB_HYS 202 ±30 VDIM MAX VDIM MIN VEN HIGH VEN Rising VEN HYS REN mV 2.56 0.3 20 0.25 50 45 0.1 fPWM RDS ON tON MIN tOFF MIN 0.3 80 2 0.5 100 100 fMAX D tSS Max 45 108 1 30 External capacitor on dim pin is 4.7nF 0.3 www.MonolithicPower.com MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2011 MPS. All Rights Reserved. V V V mV kΩ kHz Ω ns ns 600 kHz 70 % ms 3 MP24892 – STEP DOWN WLED DRIVER WITH WIDE 6V–45V INPUT VOLTAGE PIN FUNCTIONS TSOT23-5 Pin# 1 2 3 Name Description Internal MOSFET Drain. Connecting the common terminal of inductor and anode of Schottky to this pin. GND Ground. Enable/Dimming. Apply a square wave signal for PWM dimming (refer to application information). Apply a 0.3V–2.5V DC voltage for analog dimming. The DC voltage linearly EN/DIM controls the LED current range from 25% to 200%. Turn off the output current when pulling this pin below 0.2V. Connect a 1nF–10nF capacitor for normal operation (VEN/DIM=1.28V). SW 4 RS LED Current Sense Input. Connect the current sense resistor to this pin. 5 IN Input Supply. Connect an appropriate decoupling capacitor from IN pin to GND. MP24892 Rev. 1.0 11/3/2011 www.MonolithicPower.com MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2011 MPS. All Rights Reserved. 4 MP24892 – STEP DOWN WLED DRIVER WITH WIDE 6V–45V INPUT VOLTAGE TYPICAL PERFORMANCE CHARACTERISTICS VIN=30V, 3 LEDS in series, IOUT=550mA, unless otherwise noted. Analog Dimming Curve 1.2 1.2 OUTPUT CURRENT (A) 95 EFFICIENCY (%) ILED vs. Rset 90 85 80 75 70 10 15 20 25 30 35 40 45 1 1 0.8 0.8 ILED(A) 100 Efficiency vs. Input Voltage 0.6 0.4 0.4 0.2 0.2 0 0 0.5 1 1.5 2 2.5 Steady State 0 0.1 Vin Startup 0.3 0.5 0.7 0.9 Ven Startup VEN 1V/div. VIN 20V/div. EN Signal 2V/div. ILED 500mA/div. ILED 500mA/div. PWM Dimming Open LED Protection Short LED Protection fPWM = 200Hz, DPWM= 50% Open LEDs at working Short LEDs at working VSW 20V/div. VSW 20V/div. PWM Signal 2V/div. VLED+ 10V/div. ILED 500mA/div. 1.1 VSW 20V/div. Vsw 20V/div. ILED 200mA/div. 3 ANALOG DIM (V) INPUT VOLTAGE (V) VSW 10V/div. 0.6 ILED 200mA/div. VSW 20V/div. VLED10V/div. ILED 200mA/div. FUNCTION DIAGRAM MP24892 Rev. 1.0 11/3/2011 www.MonolithicPower.com MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2011 MPS. All Rights Reserved. 5 MP24892 – STEP DOWN WLED DRIVER WITH WIDE 6V–45V INPUT VOLTAGE Figure 1: MP24892 Functional Block Diagram MP24892 Rev. 1.0 11/3/2011 www.MonolithicPower.com MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2011 MPS. All Rights Reserved. 6 MP24892 – STEP DOWN WLED DRIVER WITH WIDE 6V–45V INPUT VOLTAGE OPERATION Steady State The MP24892 is a hysteretic-controlled stepdown LED driver that is easily configured for various applications with an input range of 6V– 45V. The converter employs a high-side current sensing resistor to detect and regulate the LED current. The voltage across the current sensing resistor is kept measured and regulated in 202mV±30mV range. The internal 1.275V reference voltage provides a 0.2V reference to enable the part and a 1.275V pull-up voltage as the current reference. When VEN>0.2V, the output of the comparator goes high and the other blocks are enabled. Output current is sensed through a high-side resistor, RSENSE. When the switch turns on, the internal resistor R2 shorts out and R1 determines the output current upper-threshold. When the switch is off, R1 and R2 determine the output current lower-threshold. The ratio of R1 and R2 determines the current hysteresis. Enable Control Once the input voltage is applied, a 2µA current is sourced out from EN/DIM pin. If EN/DIM is left open, the IC will automatically start up to the maximum brightness. Applying a capacitor on this pin programs a soft start time. MP24892 Rev. 1.0 11/3/2011 Applying an external voltage in the range of 0.2V to 1.25V to this pin linearly controls the current sensing voltage reference from 0mV to 202mV for analog dimming. Applying an external PWM signal with an amplitude of approximately 1.25V to this pin enables PWM dimming. For more on the flexible external PWM dimming method, please refer to the selecting dimming control mode section. System Soft-Start The voltage on the EN/DIM pin functions as the inductor current reference. An external capacitor from the EN/DIM pin to ground provides a softstart delay. When VIN starts, the internal voltage source charges the capacitor from 0V to 1.25V. Dimming Control MP24892 provides two dimming methods: PWM dimming and DC analog dimming. To use PWM dimming, apply a square wave to the EN/DIM pin. To use analog dimming, apply a 0.3V–2.5V DC voltage to this pin. www.MonolithicPower.com MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2011 MPS. All Rights Reserved. 7 MP24892 – STEP DOWN WLED DRIVER WITH WIDE 6V–45V INPUT VOLTAGE APPLICATION INFORMATION Setting the LED Current The LED current is set by the current sense resistor between the IN pin and RS pin. RSENSE=202mV/ILED For RSET=0.36Ω, the LED current is set to 550mA Selecting the Inductor A lower inductance value results in a higher switching frequency, which causes greater switching losses. Select a switching frequency between 200kHz to 600kHz for most application. Estimate the inductor value using the equation below, where fSW is the switching frequency: V (1- OUT )  VOUT VIN L 0.3  ILED  fSW For higher efficiency, select an inductor with the lowest DC resistance possible. Selecting the Diode The output diode supplies current to the inductor when the internal MOSFET is off. To reduce losses due to diode forward voltage and recovery time, use a Schottky diode rated for a reverse voltage greater than the input voltage. The average current rating must exceed the maximum expected load current, and the peak current rating must exceed the peak inductor current. Selecting the Input Capacitor The input capacitor reduces the surge current drawn from the input supply and the switching noise from the device. Use a 10µF–22µF capacitor with a voltage rating that exceeds the input voltage for most applications. Select a capacitor with low ESR. Selecting the Output Capacitor An output capacitor is not necessary for most applications, but if the peak-to-peak ripple LED current must be less than 30% of the average current, add a capacitor across the LEDs. The ripple current is inversely proportional to the capacitor value. Use a 2.2µF capacitor for most applications. Selecting Soft-Start Capacitor The delay time can be estimated as 0.2ms/nF with the soft-start capacitor. In PWM dimming, MP24892 Rev. 1.0 11/3/2011 use a capacitor CIN