AMS1072 DESCRIPTION FEATURES The AMS1072 is a step-up converter designed for driving up to 39 white LEDs (13 strings of 3 LEDs each) from a 5V system rail. The AMS1072 uses a current mode, fixed frequency architecture to regulate the LED current, which is measured through an external current sense resistor. Its low 104mV feedback voltage reduces power loss and improves efficiency. The OV pin monitors the output voltage and turns off the converter if an over-voltage condition is present due to an open circuit condition. • • • • • • • • • • • The AMS1072 includes under-voltage lockout, current limiting and thermal overload protection preventing damage in the event of an output overload. 2.5V to 8V Input Voltage Range On Board Power MOSFET Drives up to 39 White LEDs at 5V Input Up to 92% Efficiency 1.3MHz Fixed Switching Frequency Open Load Shutdown Low 104mV Feedback Voltage Soft-Start/PWM Dimming UVLO, Thermal Shutdown Internal 1.3A Current Limit Available in SOT23-6 Packages APPLICATIONS • • • • The AMS1072 is available in small 6-pin SOT23-6 packages. Cell Phones Handheld Computers and PDAs Digital Still Cameras Small LCD Displays TYPICAL APPLICATION VIN 4V - 6V 13 Strings IN EN EN SW AMS1072 GND OV FB 1 Advanced Monolithic Systems http://www.ams-semitech.com AMS1072 PACKAGE REFERENCE TOP VIEW SW 1 6 IN GND 2 5 OV FB 3 4 EN Part Number Package Temperature AMS1072 SOT23-6 –40°C to +85°C ABSOLUTE MAXIMUM RATINGS SW Pin......................................–0.5V to +28.5V All Other Pins ..............................–0.3V to +8V Storage Temperature.............. –65°C to +150°C Recommended Operating Conditions IN Supply Voltage ..............................2.5V to 8V Output Voltage ....................................VIN to 25V Operating Temperature............. –40°C to +85°C ELECTRICAL CHARACTERISTICS VIN = VEN = 5V, TA = +25°C, unless otherwise noted. Parameters Symbol Condition Operating Input Voltage Supply Current (Shutdown) Supply Current (Quiescent) Switching Frequency Maximum Duty Cycle Under Voltage Lockout IN Under Voltage Lockout Under Voltage Lockout Hysteresis Open Lamp Shutdown Threshold Min VIN 2.5 VEN = 0V VFB = 0.15V VOV Max Units 8 1 750 1.5 V µA µA MHz % VFB = 0V 1.0 85 0.1 690 1.3 92 VIN Rising 2.25 2.45 V 92 mV 28 V fSW UVLO Typ V OV Rising 2 Advanced Monolithic Systems http://www.ams-semitech.com ELECTRICAL CHARACTERISTICS (continued) AMS1072 VIN = VEN = 5V, TA = +25°C, unless otherwise noted. Parameters Symbol Condition Enable EN Threshold EN Threshold EN Hysteresis EN Input Bias Current Feedback FB Voltage FB Input Bias Current Output Switch SW On-Resistance SW Current Limit VEN Rising, VIN = 5V VEN Rising, VIN = 2.5V Min Typ Max Units 1.1 0.8 1.35 1.6 V V mV µA 114 mV nA 90 1 VEN = 0V, 5V 94 –600 VFB = 0.1V R ON Duty Cycle = 60% Thermal Shutdown 104 –300 0.5 1.33 Ω A 160 °C PIN FUNCTIONS SOT23-6 Pin # Name Description 1 SW 2 GND 3 FB 4 EN 5 OV 6 IN Power Switch Output. SW is the drain of the internal MOSFET switch. Connect the power inductor and output rectifier to SW. Ground. Feedback Input. The AMS1072 regulates the voltage across the current sense resistor between FB and GND. Connect a current sense resistor from the bottom of the LED string to GND. Connect the bottom of the LED string to FB. The regulation voltage is 104mV. Regulator On/Off Control Input. A high input at EN turns on the converter, and a low input turns it off. When not used, connect EN to the input source for automatic startup. The EN pin cannot be left floating. Over Voltage Input. OV measures the output voltage for open circuit protection. Connect OV to the output at the top of the LED string. Input Supply Pin. Must be locally bypassed. 3 Advanced Monolithic Systems http://www.ams-semitech.com AMS1072 Functional Block Diagram FB + - CONTROL LOGIC + AMPLIFIER M1 SW PWM COMPARATOR 104mV + + CURRENT SENSE AMPLIFIER 1.3MHz OSC APPLICATION INFORMATION VIN 4V to 6V MBR0520 IN EN 9 Strings Total SW AMS1072 GND OV FB ILED = 104mV × R1 + R2 R1 × R2 4 Advanced Monolithic Systems http://www.ams-semitech.com GND AMS1072 Dimming Control VDC LED1 LED2 LED3 AMS1072 FB Dimming Control Using a DC Voltage LED1 LED1 AMS1072 LED2 PWM EN FB LED3 LED3 AMS1072 LED2 PWM FB 1KHz or below PWM signal is above 1KHz Dimming Control Using a Logic Signal Dimming Control Using a Filtered PWM Signal 5 Advanced Monolithic Systems http://www.ams-semitech.com AMS1072 PACKAGE INFORMATION SOT23-6 0.95 BSC 0.60 TYP 2.80 3.00 6 4 1.20 TYP 1.50 1.70 1 2.60 TYP 2.60 3.00 3 TOP VIEW RECOMMENDED LAND PATTERN 0.84 0.90 1.00 MAX 0.09 0.20 SEATING PLANE 0.30 0.50 0.95 BSC 0.00 0.10 SEE DETAIL "A" FRONT VIEW SIDE VIEW GAUGE PLANE 0.25 BSC 0o-8o NOTE: 0.30 0.50 ALL DIMENSIONS ARE IN MILLIMETERS. 6 Advanced Monolithic Systems http://www.ams-semitech.com