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LT1309 500kHz Micropower DC/DC Converter for Flash Memory
FEATURES
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DESCRIPTIO
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60mA Output Current at 12V from 3V or 5V Supply Shutdown to 9A VPP VALID Comparator Up to 85% Efficiency Switching Frequency: 500kHz (Typical) Quiescent Current: 650A 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
APPLICATI
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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
The LT (R) 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 650A decreasing to 9A 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.
, LTC and LT are registered trademarks of Linear Technology Corporation. Burst Mode is a trademark of Linear Technology Corporation.
TYPICAL APPLICATI
VIN 3.3V TO 5V VIN VPP VALID ON/OFF
12V, 60mA Flash Memory Programming Supply
L1* 10H D1
86
VPP 12V, 60mA
84 82
EFFICIENCY (%)
VSW
+
C1 4.7F
VPP VALID SENSE LT1309 SOFT ON/OFF START PGND GND
80 78 76 74 72 VIN = 3.3V
R1 1M
C2 1F** C3 0.1F
* MURATA ERIE LQH3C100K0YM00 ** CERAMIC MOTOROLA MBR0530
LT1309 * TA01
70 1 10 LOAD CURRENT (mA) 100
LT1309 * TA02
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12V Output Efficiency
VIN = 5V
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UO
1
LT1309 ABSOLUTE AXI U RATI GS
PACKAGE/ORDER I FOR ATIO
TOP VIEW SOFT START 1 VCC 2 PGND 3 VSW 4 8 7 6 5 ON/OFF SENSE VPP VALID GND
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 ..................... 0C to 70C Storage Temperature Range ................. - 65C to 150C Lead Temperature (Soldering, 10 sec).................. 300C
ORDER PART NUMBER LT1309CS8 S8 PART MARKING 1309
S8 PACKAGE 8-LEAD PLASTIC SO
TJMAX = 150C, JA = 150C/W
Consult factory for Industrial and Military grade parts.
ELECTRICAL CHARACTERISTICS
SYMBOL IQ PARAMETER Quiescent Current Quiescent Current, Shutdown Input Voltage Range Output Sense Voltage Output Referred Comparator Hysteresis fOSC DC tON VCESAT Oscillator Frequency Maximum Duty Cycle Switch ON Time Reference Line Regulation Switch Saturation Voltage Switch Leakage Current Switch Current Limit Soft Start Current ON/OFF Input Voltage Low ON/OFF Input Voltage High ON/OFF Bias Current
TA = 25C, VCC = 5V, VON/OFF = 3V, unless otherwise noted.
MIN TYP 650 9 2
q
CONDITIONS VSENSE = 12V VON/OFF = 0.2V
MAX 900 15 6 12.6 700 92 0.15 350 10 900 950 120 0.8
UNITS A A V V mV kHz % s %/V mV A mA mA A V V A A A A A V V
11.5 400
12 35 500 85 1.7 0.06 230 0.1
Current Limit Not Asserted
q
80
2V < VIN < 6V ISW = 0.5A VSW = 12V, Switch Off VIN = 5V, Soft Start Floating VIN = 3V, Soft Start Floating Soft Start Grounded 1.6 VON/OFF = 5V VON/OFF = 3V VON/OFF = 0V VON/OFF = 0.2V 400 450
600 650 80
16.0 8.0 0.1 50.0 0.1 VSENSE - 200mV 0.13 4 4.5
24.0 14.0 1.0 90 1 0.3
Sense Pin Input Current VPP VALID Threshold VPP VALID Output Voltage Low VPP VALID Output Voltage High VSENSE Rising (High to Low Transition) ISINK = 100A ISOURCE = 2.5A
The q denotes specifications which apply over the full operating temperature range.
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LT1309 TYPICAL PERFORMANCE CHARACTERISTICS
Oscillator Frequency
800 1000 900
SWITCH SATURATION VOLTAGE (mV)
OSCILLATOR FREQUENCY (kHz)
SWITCH CURRENT (mA)
700
600
500
400
300 -50
-25
0 25 50 TEMPERATURE (C)
Sense Voltage
12.20 12.15
SUPPLY CURRENT (A)
SENSE VOLTAGE (V)
12.10 12.05 12.00 11.95 11.90 11.85 11.80 -50 -25 50 25 TEMPERATURE (C) 0 75 100
1309 G04
Supply Current in Shutdown
14 12 10 8 6 4 2 0 -50 VCC = 3V VCC = 5V
MAXIMUM DUTY CYCLE (%)
SUPPLY CURRENT (A)
-25
50 25 0 TEMPERATURE (C)
UW
75
1309 G01
Switch Current Limit
250
Switch Saturation Voltage
ISW = 500mA 225 200 175 150 125 100 -50
800 VCC = 3V 700 VCC = 5V 600 500 400 -50
100
-25
0 25 50 TEMPERATURE (C)
75
100
1309 G02
-25
0 25 50 TEMPERATURE (C)
75
100
1309 G03
Supply Current
800
700
VCC = 5V VCC = 3V
600
500
400
300 -50
-25
0 25 50 TEMPERATURE (C)
75
100
1309 G05
Maximum Duty Cycle
95
90
85
80
75
75
100
1309 G06
70 -50
-25
0 25 50 TEMPERATURE (C)
75
100
1309 G07
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LT1309 TYPICAL PERFORMANCE CHARACTERISTICS
Start-Up Waveforms, ILOAD = 1mA
12V VOUT 2V/DIV IL 500mA/DIV VON/OFF 10V/DIV 50s/DIV
1309 G08
VPP VALID 10V/DIV VON/OFF 10V/DIV
PI FU CTIO S
SOFT START (Pin 1): A 0.1F/1M parallel RC from this pin to GND provides a Soft Start function upon device turn-on. Initially about 80A 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 1F 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. 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 < 1A. ON/OFF (Pin 8): Shutdown Control. When pulled below 1.5V, this pin disables the LT1309 and reduces supply current to 9A. All circuitry is disabled in shutdown. The part is enabled when ON/OFF is greater than 1.5V.
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UW
Start-Up Waveforms, ILOAD = 10mA
VOUT 5V/DIV
50s/DIV
1309 G09
Load Transient Response, COUT = 1F
12V OUTPUT 1V/DIV AC COUPLED 60mA 10mA
ILOAD
50s/DIV
1309 G10
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LT1309
BLOCK DIAGRA
SENSE 7
864k
4k OFF C1 500kHz OSCILLATOR
VREF 1.24V
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
+
100k
-
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ON/OFF 8 POWER ON VCC C3 36mV VCC 2
+ +-
200k
- +
-
VPP VALID Q3 1
R2 700
R1 3
C2
6
BIAS SW 4 Q2 x1 Q1 x 50
SOFT START
5 GND
3 PGND
1309 BD
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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 1F/0.1F parallel RC to the Soft Start pin limits inrush current during start-up.
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LT1309
APPLICATIONS INFORMATION
Inductor Selection The low inductance value required with the LT1309 (10H) 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. Capacitor Selection The LT1309 needs very little input and output capacitance to function. Output capacitance should be 1F or 2F 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 0.1F ceramic units. Lower ripple can be obtained by increasing the capacitance to the 5F to 10F level. 2F to 5F 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. 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. 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.
VIN L1
D1
VOUT GND
1309 F01
Figure 1. LT1309 Recommended Layout
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W
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R1 C3
1
8
ON/OFF
C1
2
7
3
6
VPP VALID
4
5
C2
LT1309
PACKAGE DESCRIPTION
0.010 - 0.020 x 45 (0.254 - 0.508) 0.008 - 0.010 (0.203 - 0.254) 0- 8 TYP
0.016 - 0.050 0.406 - 1.270 *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.
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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
0.228 - 0.244 (5.791 - 6.197)
0.150 - 0.157** (3.810 - 3.988)
1
2
3
4
0.053 - 0.069 (1.346 - 1.752)
0.004 - 0.010 (0.101 - 0.254)
0.014 - 0.019 (0.355 - 0.483)
0.050 (1.270) BSC
SO8 0695
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LT1309 RELATED PARTS
PART NUMBER
LT1106 LT1109-12 LT1109A-12 LTC (R)1262 LT1303
DESCRIPTION
Micropower Step-Up DC/DC Converter, 12V at 60mA Micropower Step-Up DC/DC Converter, 12V at 60mA Micropower Step-Up DC/DC Converter, 12V at 120mA Inductorless Flash Memory Programming Supply, 12V at 30mA Micropower High Efficiency DC/DC Converter with Low-Battery Detector
COMMENTS
Thin TSSOP Package for Type I PCMCIA Card Flash Memory VPP Generator, Adjustable Also VPP Generator, Adjustable Also Switched Capacitor Converter, No Inductor Adjustable and Fixed 5V, IOUT up to 200mA
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Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900 q FAX: (408) 434-0507 q TELEX: 499-3977
LT/GP 0896 7K * PRINTED IN THE USA
(c) LINEAR TECHNOLOGY CORPORATION 1995

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