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LT1302/LT1302-5

Micropower

High Output Current

Step-Up Adjustable and

Fixed 5V DC/DC Converters

Figure 1. 2-Cell to 5V/600mA DC/DC Converter

ESCRIPTIO

■

5V at 600mA or 12V at 120mA from 2-Cell Supply

■

200µA Quiescent Current

■

Logic Controlled Shutdown to 15µA

■

Low V

CESAT

Switch: 310mV at 2A Typical

■

Burst Mode

Operation at Light Load

■

Current Mode Operation for Excellent

Line and Load Transient Response

■

Available in 8-Lead SO or PDIP

■

Operates with Supply Voltage as Low as 2V

The LT

1302/LT1302-5 are micropower step-up DC/DC

converters that maintain high efficiency over a wide

range of output current. They operate from a supply

voltage as low as 2V and feature automatic shifting

between Burst Mode operation at light load, and current

mode operation at heavy load.

The internal low loss NPN power switch can handle

current in excess of 2A and switch at frequencies up to

400kHz. Quiescent current is just 200µA and can be

further reduced to 15µA in shutdown.

Available in 8-pin PDIP or 8-pin SO packaging, the LT1302/

LT1302-5 have the highest switch current rating of any

similarly packaged switching regulators presently on the

market.

, LTC and LT are registered trademarks of Linear Technology Corporation.

Burst Mode is a trademark of Linear Technology Corporation.

■

Notebook and Palmtop Computers

■

Portable Instruments

■

Personal Digital Assistants

■

Cellular Telephones

■

Flash Memory

ITY

C3

0.1µF

SHUTDOWN

PGND

SHDN

SENSE

GND



20k



0.01µF

C1

100µF

C2

100µF

L1

10µH

2 CELLS

LT1302 • F01

C1 = C2 = SANYO OS-CON

L1 = COILTRONICS CTX10-3

COILCRAFT DO3316-103



OUTPUT

5V

600mA



D1 = MOTOROLA MBRS130LT3

LT1302-5

LOAD CURRENT (mA)

EFFICIENCY (%)

10 100 1000

LT1302 • TA02

= 3V

= 2.5V

= 2V

2-Cell to 5V Converter Efficiency

Summary of content (16 pages)

PAGE 1
LT1302/LT1302-5 Micropower High Output Current Step-Up Adjustable and Fixed 5V DC/DC Converters U DESCRIPTIO FEATURES ■ ■ ■ ■ ■ ■ ■ ■ 5V at 600mA or 12V at 120mA from 2-Cell Supply 200µA Quiescent Current Logic Controlled Shutdown to 15µA Low VCESAT Switch: 310mV at 2A Typical Burst ModeTM Operation at Light Load Current Mode Operation for Excellent Line and Load Transient Response Available in 8-Lead SO or PDIP Operates with Supply Voltage as Low as 2V UO APPLICATI ■ ■ ■ ■ The internal low loss NPN
PAGE 2
LT1302/LT1302-5 U U RATI GS W W W W AXI U U ABSOLUTE PACKAGE/ORDER I FOR ATIO VIN Voltage ............................................................. 10V SW Voltage ............................................................. 25V FB Voltage .............................................................. 10V SHDN Voltage ......................................................... 10V VC Voltage ................................................................ 4V IT Voltage ..........................
PAGE 3
LT1302/LT1302-5 U W TYPICAL PERFORMANCE CHARACTERISTICS No-Load Quiescent Current Circuit of Figure 1 Switch Saturation Voltage 400 TA = 25°C TA = 25°C 450 ISW = 2A 400 350 SATURATION VOLTAGE (mV) 500 400 VCESAT (V) QUIESCENT CURRENT (µA) Switch Saturation Voltage 600 500 300 250 200 300 200 150 100 100 350 300 250 200 150 50 0 2.0 0 2.5 3.0 3.5 4.0 SUPPLY VOLTAGE (V) 4.5 5.
PAGE 4
LT1302/LT1302-5 U W TYPICAL PERFORMANCE CHARACTERISTICS Shutdown Pin Bias Current Oscillator Frequency Maximum Duty Cycle 100 300 20 TA = 25°C 18 FREQUENCY (kHz) DUTY CYCLE (%) 90 80 70 60 SHUTDOWN CURRENT (µA) 275 250 225 200 175 16 14 12 10 8 6 4 2 50 –50 –25 0 25 50 TEMPERATURE (°C) 75 100 150 –50 –25 75 0 25 50 TEMPERATURE (°C) 1302 G10 0 100 0 1 6 4 2 3 5 SHUTDOWN VOLTAGE (V) 1302 G11 LT1302-5 Output Voltage vs Load Current 7 8 1302 G12 Maximum Output Power* Boost Mo
PAGE 5
LT1302/LT1302-5 U U U PI FU CTIO S SW (Pin 7): Switch Pin. Connect inductor and diode here. Keep layout short and direct. and 8 are thermally connected to the die. One square inch of PCB copper provides an adequate heat sink for the device. PGND (Pin 8): Power Ground. Pins 8 and 1 should be connected under the package. In the SO package, pins 1 W BLOCK DIAGRA SM D1 L1 VIN C1 + 6 C3 7 VIN 36mV R5 730Ω A2 – 1.
PAGE 6
LT1302/LT1302-5 W BLOCK DIAGRA SM SENSE VIN SW 4 6 7 36mV R4 1.75Ω + R5 730Ω A2 R1 315k – 1.24V REFERENCE CMP1 + OFF ENABLE – 3 Q5 – SHUTDOWN Q3 Q4 160X DRIVER VIN VIN Q1 A1 SHDN A3 HYSTERETIC COMPARATOR 2µA VOS 15mV R2 105k 220kHz OSCILLATOR Q2 BIAS + ERROR AMPLIFIER 300Ω 3.6k 1 2 5 8 GND VC IT PGND 1302 F03 Figure 3. LT1302-5 Block Diagram OPERATIO U The LT1302’s operation can best be understood by examining the block diagram in Figure 2.
PAGE 7
LT1302/LT1302-5 OPERATIO U CMP1 stays on and the peak switch current is regulated by the voltage on the VC pin (A1’s output). VC drives the base of Q1. As the VC voltage rises, Q2 conducts less current, resulting in less drop across R5. Q4’s peak current must then increase in order for A2 to trip. This current mode control results in good stability and immunity to input voltage variations. Because this is a linear, closed-loop system, frequency compensation is required.
PAGE 8
LT1302/LT1302-5 U W U U APPLICATIONS INFORMATION and there is no low frequency component. The total ESR is under 0.03Ω. If a single 100µF aluminum electrolytic capacitor is used instead, the converter mode-hops between current mode and Burst Mode due to high ESR, causing the voltage comparator to trip as shown in Figure 5. The ripple voltage is now over 500mVP-P and contains a low frequency component.
PAGE 9
LT1302/LT1302-5 U U W U APPLICATIONS INFORMATION Frequency Compensation Obtaining proper RC values for the frequency compensation network is largely an empirical procedure, since variations in input and output voltage, topology, capacitor ESR and inductance make a simple formula elusive. As an example, consider the case of a 2.5V to 5V boost converter supplying 500mA. To determine optimum compensation, the circuit is built and a transient load is applied to the circuit. Figure 7 shows the setup.
PAGE 10
LT1302/LT1302-5 U U W U APPLICATIONS INFORMATION IT Pin VOUT 100mV/DIV AC COUPLED ILOAD The IT pin is used to disable Burst Mode, forcing the LT1302 to operate in current mode even at light load. To disable Burst Mode, 3.3k resistor R1 is connected from IT to gound. More conservative frequency compensation must be used when in this mode. A 0.1µF capacitor and 4.7k resistor from VC to ground has been found to be adequate.
PAGE 11
LT1302/LT1302-5 U U W U APPLICATIONS INFORMATION ally reaches audio frequencies, but at a much lighter load than without the IT feature. At some input voltage/load current combinations, some residual bursting may occur at frequencies out of the audio band. Figure 8c details efficiency with and without the addition of R1. Burst Mode operation keeps efficiency high at light load with IT floating. Efficiency falls off at light load with R1 added because the LT1302 cannot transition into Burst Mode.
PAGE 12
LT1302/LT1302-5 U W U U APPLICATIONS INFORMATION separate ground trace up under the package as shown. The battery and load return should go to the power side of the ground copper. Thermal Considerations The LT1302 contains a thermal shutdown feature which protects against excessive internal (junction) temperature. If the junction temperature of the device exceeds the protection threshold, the device will begin cycling between normal operation and an off state. The cycling is not harmful to the part.
PAGE 13
LT1302/LT1302-5 U W U U APPLICATIONS INFORMATION As an example, consider a boost converter with the following specifications: VIN = 3V VOUT = 6V IOUT = 700mA Total power loss in the LT1302, assuming R = 0.15Ω and VD = 0.45V, is: ( PD = 700mA 2           0.7 6 + 0.45 − 3  6 + 0.45 6 + 0.45 0.15Ω   − + × × . . . . 0 7 6 0 15 0 7 6 0 15 27 × ×       3 −  3−       3 3   )( 2 ) ( )( ) = 223mW + 89mW = 312mW Using the CS8 package with 100 sq.
PAGE 14
LT1302/LT1302-5 U TYPICAL APPLICATIONS Single Cell to 5V/150mA Converter 5V/150mA OUTPUT L1 3.3µH D1 220Ω 10Ω R1 301k 1% 2N3906 (169k FOR 3.3V) 100k 1.5V CELL 100k IL SET 100k VIN SW VIN SW1 LT1073 FB GND SHDN FB LT1302 AO IT PGND SW2 56.2k 1% VC GND 100pF 4.99k 1% 20k + C1 47µF L1 = COILCRAFT DO3316-332 D1 = MOTOROLA MBRS130LT3 C2 220µF + 0.1µF 0.01µF C1 = AVX TPSD476M016R0150 C2 = AVX TPSE227M010R0100 COILCRAFT (708) 639-2361 36.
PAGE 15
LT1302/LT1302-5 U TYPICAL APPLICATIONS 3 Cell to 3.3V Buck-Boost Converter with Auxiliary 12V Regulated Output VIN 2.5V-8V 10Ω SHUTDOWN SHDN FB 169k 1% 200pF VC GND 6 T1D T1E 4 5 + C3 47µF 16V VIN SW D2 LT1302 100k 1% 7 13V 0.1µF IT PGND 2 + C1 100µF 16V D1 24k 4700pF IN 1 T1C T1A 12V 120mA OUT + 22µF 9 25V 330k 1% LT1121 SHDN 3 8 T1B + ADJ GND + C2 330µF 6.3V 3.3µF 150k 1% 10 1302 TA05 3.
PAGE 16
LT1302/LT1302-5 U PACKAGE DESCRIPTION Dimensions in inches (millimeters) unless otherwise noted. N8 Package 8-Lead Plastic DIP 0.400* (10.160) MAX 8 7 6 5 1 2 3 4 0.255 ± 0.015* (6.477 ± 0.381) 0.300 – 0.325 (7.620 – 8.255) 0.065 (1.651) TYP 0.009 – 0.015 (0.229 – 0.381) ( +0.025 0.325 –0.015 8.255 +0.635 –0.381 0.130 ± 0.005 (3.302 ± 0.127) 0.045 – 0.065 (1.143 – 1.651) 0.125 (3.175) MIN 0.045 ± 0.015 (1.143 ± 0.381) ) 0.018 ± 0.003 (0.457 ± 0.076) 0.100 ± 0.010 (2.540 ± 0.254) 0.