LT1309 500kHz Micropower DC/DC Converter for Flash Memory U DESCRIPTIO FEATURES ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ The LT ® 1309 is a 500kHz micropower DC/DC converter for Flash Memory. The regulator features Burst ModeTM operation with a 0.5A, 300mV switch, enabling 85% efficiency at the fixed 12V output. High frequency operation permits the use of small value, and therefore small size, surface mount inductors and capacitors. The LT1309 comes in an 8-lead SO package allowing extremely compact PC board layouts. These features make the device attractive for PCMCIA cards, cellular phones and other applications where PC board space is limited. Quiescent current is 650µA decreasing to 9µA when the part shuts down. The device includes a soft start feature which limits supply current transients during turn-on. The LT1309 contains a VPP VALID comparator with a logic output that goes low when the output voltage is ready to program 12V Flash Memory. This comparator simplifies the interface to external control logic. 60mA Output Current at 12V from 3V or 5V Supply Shutdown to 9µA VPP VALID Comparator Up to 85% Efficiency Switching Frequency: 500kHz (Typical) Quiescent Current: 650µA Low VCESAT Switch: 300mV at 0.5A (Typical) Soft Start Reduces Supply Current Transients Uses Low Value, Small Size, Surface Mount Inductors Available in 8-Lead SO Package UO APPLICATI ■ ■ ■ ■ ■ ■ S Flash Memory VPP Generators Type II and III PCMCIA Card DC/DC Converters 3V to 12V, 5V to 12V Converters Portable Computers and Instruments Cellular Telephones DC/DC Converter Module Replacements , LTC and LT are registered trademarks of Linear Technology Corporation. Burst Mode is a trademark of Linear Technology Corporation. UO TYPICAL APPLICATI 12V, 60mA Flash Memory Programming Supply L1* 10µH VIN 3.3V TO 5V D1† 12V Output Efficiency 86 VPP 12V, 60mA VIN = 5V 84 VPP VALID ON/OFF + C1 4.7µF VPP VALID SENSE LT1309 SOFT ON/OFF START PGND GND * MURATA ERIE LQH3C100K0YM00 ** CERAMIC † MOTOROLA MBR0530 82 VSW R1 1M C2 1µF** C3 0.1µF EFFICIENCY (%) VIN 80 VIN = 3.3V 78 76 74 72 LT1309 • TA01 70 1 10 LOAD CURRENT (mA) 100 LT1309 • TA02 1 LT1309 U U RATI GS W W W W AXI U U ABSOLUTE PACKAGE/ORDER I FOR ATIO VCC Voltage ............................................................... 7V VSW Voltage ............................................................ 20V VSENSE Voltage ....................................................... 20V VON/OFF Voltage......................................................... 7V VSEL Voltage ............................................................. 7V ILIM Voltage .............................................................. 7V Maximum Power Dissipation ............................ 500mW Operating Temperature Range ..................... 0°C to 70°C Storage Temperature Range ................. – 65°C to 150°C Lead Temperature (Soldering, 10 sec).................. 300°C ORDER PART NUMBER TOP VIEW SOFT START 1 8 ON/OFF VCC 2 7 SENSE PGND 3 6 VPP VALID VSW 4 5 GND LT1309CS8 S8 PART MARKING S8 PACKAGE 8-LEAD PLASTIC SO 1309 TJMAX = 150°C, θJA = 150°C/W Consult factory for Industrial and Military grade parts. ELECTRICAL CHARACTERISTICS TA = 25°C, VCC = 5V, VON/OFF = 3V, unless otherwise noted. SYMBOL PARAMETER CONDITIONS IQ Quiescent Current VSENSE = 12V Quiescent Current, Shutdown VON/OFF = 0.2V MIN Input Voltage Range ● DC Maximum Duty Cycle tON Switch ON Time VCESAT UNITS 650 900 µA 9 15 µA 6 V 12.6 V 11.5 12 400 500 700 kHz 80 85 92 % Output Referred Comparator Hysteresis Oscillator Frequency MAX 2 Output Sense Voltage fOSC TYP 35 Current Limit Not Asserted ● µs 1.7 Reference Line Regulation 2V < VIN < 6V 0.06 0.15 %/V Switch Saturation Voltage ISW = 0.5A 230 350 mV Switch Leakage Current VSW = 12V, Switch Off Switch Current Limit VIN = 5V, Soft Start Floating VIN = 3V, Soft Start Floating Soft Start Current Soft Start Grounded 400 450 0.1 10 µA 600 650 900 950 mA mA 80 120 µA 0.8 V ON/OFF Input Voltage Low ON/OFF Input Voltage High ON/OFF Bias Current 1.6 VPP VALID Threshold V VON/OFF = 5V VON/OFF = 3V VON/OFF = 0V 16.0 8.0 0.1 24.0 14.0 1.0 µA µA µA VON/OFF = 0.2V 50.0 0.1 90 1 µA µA 0.3 V Sense Pin Input Current VSENSE Rising (High to Low Transition) VPP VALID Output Voltage Low ISINK = 100µA VPP VALID Output Voltage High ISOURCE = 2.5µA The ● denotes specifications which apply over the full operating temperature range. 2 mV VSENSE – 200mV 0.13 4 4.5 V LT1309 U W TYPICAL PERFORMANCE CHARACTERISTICS Oscillator Frequency Switch Current Limit SWITCH SATURATION VOLTAGE (mV) SWITCH CURRENT (mA) 600 500 400 800 VCC = 3V 700 VCC = 5V 600 500 –25 75 0 25 50 TEMPERATURE (°C) 400 –50 100 –25 0 25 50 TEMPERATURE (°C) 75 ISW = 500mA 225 200 175 150 125 100 –50 100 –25 0 25 50 TEMPERATURE (°C) 1309 G02 1309 G01 Sense Voltage 75 100 1309 G03 Supply Current 800 12.20 700 12.10 SUPPLY CURRENT (µA) SENSE VOLTAGE (V) 12.15 12.05 12.00 11.95 11.90 VCC = 5V VCC = 3V 600 500 400 11.85 11.80 –50 –25 0 50 25 TEMPERATURE (°C) 75 300 –50 100 –25 0 25 50 TEMPERATURE (°C) 75 1309 G04 100 1309 G05 Supply Current in Shutdown Maximum Duty Cycle 95 14 MAXIMUM DUTY CYCLE (%) 12 SUPPLY CURRENT (µA) OSCILLATOR FREQUENCY (kHz) 250 900 700 300 –50 Switch Saturation Voltage 1000 800 VCC = 5V 10 8 6 VCC = 3V 4 90 85 80 75 2 0 –50 –25 50 25 0 TEMPERATURE (°C) 75 100 1309 G06 70 –50 –25 0 25 50 TEMPERATURE (°C) 75 100 1309 G07 3 LT1309 U W TYPICAL PERFORMANCE CHARACTERISTICS Start-Up Waveforms, ILOAD = 1mA Start-Up Waveforms, ILOAD = 10mA 12V VOUT 5V/DIV VOUT 2V/DIV IL 500mA/DIV VPP VALID 10V/DIV VON/OFF 10V/DIV VON/OFF 10V/DIV 50µs/DIV 50µs/DIV 1309 G08 1309 G09 Load Transient Response, COUT = 1µF 12V OUTPUT 1V/DIV AC COUPLED ILOAD 60mA 10mA 50µs/DIV 1309 G10 U U U PI FU CTIO S SOFT START (Pin 1): A 0.1µF/1MΩ parallel RC from this pin to GND provides a Soft Start function upon device turn-on. Initially about 80µA will flow from the pin into the capacitor. When the voltage at the pin reaches approximately 0.4V, current ceases flowing out of the pin. VCC (Pin 2): Input Supply. At least 1µF input bypass capacitance is required. More capacitance reduces ringing on the supply line. PGND (Pin 3): Power Ground. Connect to ground plane. VSW (Pin 4): Collector of Power Switch. High dV/dt present on this pin. To minimize radiated noise keep layout short and direct. 4 GND (Pin 5): Signal Ground. Connect to ground plane. VPP VALID (Pin 6): This pin provides a logic signal indicating that output voltage has reached 12V. Active low with internal 200k pull-up resistor. SENSE (Pin 7): Output Sense Pin. This pin connects to a resistive divider that sets the output voltage. In shutdown, the resistor string is disconnected and current into this pin reduces to < 1µA. ON/OFF (Pin 8): Shutdown Control. When pulled below 1.5V, this pin disables the LT1309 and reduces supply current to 9µA. All circuitry is disabled in shutdown. The part is enabled when ON/OFF is greater than 1.5V. LT1309 W BLOCK DIAGRA SENSE ON/OFF 7 8 VCC + + – VCC 864k – R2 700Ω C3 – 200k C2 2 36mV POWER ON 6 VPP VALID Q3 R1 3Ω BIAS + 4k – 100k + 1 SW SOFT START 4 OFF C1 VREF 1.24V Q2 ×1 500kHz OSCILLATOR Q1 × 50 5 3 GND PGND 1309 BD U OPERATIO The LT1309 is a current limited, Burst Mode (gated oscillator) type switching regulator that produces a 12V output from a 3.3V or 5V input. Operation can best be understood by referring to the Block Diagram. When the voltage at the Sense pin (Pin 7) is less than 12V, comparator C1 enables the oscillator, turning switches Q1 and Q2 on. The switch turns off when current limit is reached or when the oscillator maximum on-time is reached. When Q2 turns off, current built up in the inductor flows into the output capacitor and load. This action occurs until the output voltage reaches 12V. During start-up, the Sense pin voltage is either 3.3V or 5V, depending on the input. The VPP VALID signal remains high until the output voltage reaches 12V, signaling correct voltage level to program flash memory. Connecting a 1µF/0.1µF parallel RC to the Soft Start pin limits inrush current during start-up. 5 LT1309 U U W U APPLICATIONS INFORMATION Inductor Selection obtained by increasing the capacitance to the 5µF to 10µF level. 2µF to 5µF of tantalum (low-Q) capacitance is recommended on the input side to reduce resonance effects which can otherwise cause hundreds of millivolts of ripple voltage at the input. The low inductance value required with the LT1309 (10µH) allows the use of very small units such as the Murata-Erie LQH3C100. Requirements for the inductor include low DCR, ability to perform efficiently at 500kHz and a saturation current rating of 700mA to 900mA. Often inductor manufacturers rate maximum current for a small inductor based on self-heating considerations. For use in switching regulators where the inductor current is not constant the maximum specified DC current can be safely exceeded. Diode Selection The LT1309’s high switching speed demands a high speed rectifier. Schottky diodes are preferred for their low forward drop and fast recovery. A suitable choice is the Motorola MBR0520. This is a 0.5A, 20V Schottky in a very small package that is 1.35mm high. Capacitor Selection The LT1309 needs very little input and output capacitance to function. Output capacitance should be 1µF or 2µF for acceptable output ripple voltage. Flash memory tolerates higher ripple voltage than might be suitable for a low noise system. The capacitor can be either a single high capacitance ceramic unit such as Tokin 1E105ZY5U-203 or Murata-Erie GRM230Y5V105Z016, or can be distributed as 10 to 20 0.1µF ceramic units. Lower ripple can be PC Board Layout The component placement shown in Figure 1 is recommended for PC board layouts. The high speed current paths are kept to a minimum distance and the switch node copper is minimized to keep radiated noise low. Notice the placement of the input decoupling capacitor next to the IC. This is necessary for best performance. R1 C3 C1 VIN L1 D1 1 8 2 7 3 6 4 5 ON/OFF VPP VALID C2 VOUT GND 1309 F01 Figure 1. LT1309 Recommended Layout 6 LT1309 U PACKAGE DESCRIPTION Dimensions in inches (millimeters) unless otherwise noted. S8 Package 8-Lead Plastic Small Outline (Narrow 0.150) (LTC DWG # 05-08-1610) 0.189 – 0.197* (4.801 – 5.004) 8 7 6 5 0.150 – 0.157** (3.810 – 3.988) 0.228 – 0.244 (5.791 – 6.197) 1 0.010 – 0.020 × 45° (0.254 – 0.508) 0.008 – 0.010 (0.203 – 0.254) 2 3 4 0.053 – 0.069 (1.346 – 1.752) 0°– 8° TYP 0.016 – 0.050 0.406 – 1.270 0.014 – 0.019 (0.355 – 0.483) *DIMENSION DOES NOT INCLUDE MOLD FLASH. MOLD FLASH SHALL NOT EXCEED 0.006" (0.152mm) PER SIDE **DIMENSION DOES NOT INCLUDE INTERLEAD FLASH. INTERLEAD FLASH SHALL NOT EXCEED 0.010" (0.254mm) PER SIDE Information furnished by Linear Technology Corporation is believed to be accurate and reliable. However, no responsibility is assumed for its use. Linear Technology Corporation makes no representation that the interconnection of its circuits as described herein will not infringe on existing patent rights. 0.004 – 0.010 (0.101 – 0.254) 0.050 (1.270) BSC SO8 0695 7 LT1309 RELATED PARTS PART NUMBER DESCRIPTION COMMENTS LT1106 Micropower Step-Up DC/DC Converter, 12V at 60mA Thin TSSOP Package for Type I PCMCIA Card LT1109-12 Micropower Step-Up DC/DC Converter, 12V at 60mA Flash Memory VPP Generator, Adjustable Also LT1109A-12 Micropower Step-Up DC/DC Converter, 12V at 120mA VPP Generator, Adjustable Also LTC ®1262 Inductorless Flash Memory Programming Supply, 12V at 30mA Switched Capacitor Converter, No Inductor LT1303 Micropower High Efficiency DC/DC Converter with Low-Battery Detector Adjustable and Fixed 5V, IOUT up to 200mA 8 Linear Technology Corporation LT/GP 0896 7K • PRINTED IN THE USA 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 ● FAX: (408) 434-0507 ● TELEX: 499-3977 LINEAR TECHNOLOGY CORPORATION 1995