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LT3494/LT3494A

3494fb

TYPICAL APPLICATION

FEATURES

APPLICATIONS

DESCRIPTION

Micropower Low Noise

Boost Converters with

Output Disconnect

The LT

3494/LT3494A are low noise boost converters

with integrated power switch, Schottky diode and output

disconnect circuitry. The parts use a novel* control tech-

nique resulting in low output voltage ripple as well as high

efﬁ ciency over a wide load current range. This technique

guarantees that the switching frequency stays above the

audio band for the entire load range. The parts feature a high

performance NPN power switch with a 350mA and 180mA

current limit for the LT3494A and LT3494 respectively. The

quiescent current is a low 65μA, which is further reduced

to less than 1μA in shutdown. The internal disconnect

circuitry allows the output voltage to be isolated from the

input during shutdown. An auxiliary reference input (CTRL

pin) overrides the internal 1.225V feedback reference with

any lower value allowing full control of the output voltage

during operation. The LT3494/LT3494A are available in a

tiny 8-lead 3mm × 2mm DFN package.

OLED Power Supply from One Li-Ion Cell

■

Low Quiescent Current

65μA in Active Mode

1μA in Shutdown Mode

■

Switching Frequency is Non-Audible Over Entire

Load Range

■

Integrated Power NPN:

350mA Current Limit (LT3494A)

180mA Current Limit (LT3494)

■

Integrated Schottky Diode

■

Integrated Output Disconnect

■

Integrated Output Dimming

■

Wide Input Range: 2.3V to 16V

■

Wide Output Range: Up to 40V

■

Tiny 8-Lead 3mm × 2mm DFN Package

■

OLED Power

■

Low Noise Power

■

MP3 Players

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

All other trademarks are the property of their respective owners.

*Patent pending.

SW CAP

SHDN

CTRL

OUT

GND

2.21M

3494 TA01a

LT3494

4.7μF

2.2μF

15μH

0.22μF

TO 4.2V

OUT

16V

16mA

LOAD CURRENT (mA)

0.1

OUT

PEAK-TO-PEAK RIPPLE (mV)

1 10 100

3494 TA01b

LT3494

FIGURE 5 CIRCUIT

100MHz MEASUREMENT BW

LOAD CURRENT (mA)

0.1

EFFICIENCY (%)

POWER LOSS (mW)

1 10 100

3494 TA01c

160

200

240

280

120

= 3.6V

LOAD FROM

CAPACITOR

LOAD FROM

OUT

Output Voltage Ripple

vs Load Current

Efﬁ ciency and Power Loss

vs Load Current

Summary of content (12 pages)

PAGE 1
LT3494/LT3494A Micropower Low Noise Boost Converters with Output Disconnect FEATURES DESCRIPTION ■ The LT®3494/LT3494A are low noise boost converters with integrated power switch, Schottky diode and output disconnect circuitry. The parts use a novel* control technique resulting in low output voltage ripple as well as high efﬁciency over a wide load current range. This technique guarantees that the switching frequency stays above the audio band for the entire load range.
PAGE 2
LT3494/LT3494A ABSOLUTE MAXIMUM RATINGS PACKAGE/ORDER INFORMATION (Note 1) VCC Voltage ...............................................................16V SW Voltage ...............................................................40V CAP Voltage ..............................................................40V VOUT Voltage .............................................................40V SHDN Voltage ...........................................................16V CTRL Voltage ................................
PAGE 3
LT3494/LT3494A ELECTRICAL CHARACTERISTICS The ● denotes the speciﬁcations which apply over the full operating temperature range, otherwise speciﬁcations are at TA = 25°C. VCC = 3V, VSHDN = VCC, unless otherwise noted. (Note 2) PARAMETER CONDITIONS CTRL Pin Bias Current VCTRL = 0.5V, Current Flows Out of Pin MIN CTRL to FB Offset VCTRL = 0.5V Maximum Shunt Current VFB = 1.3V, VCAP = 5V Note 1: Stresses beyond those listed under Absolute Maximum Ratings may cause permanent damage to the device.
PAGE 4
LT3494/LT3494A TYPICAL PERFORMANCE CHARACTERISTICS Output Voltage vs Temperature 100 51.0 LT3494 1.5 FIGURE 5 CIRCUIT VCC = 3.6V NO LOAD 50.5 1.0 0.5 0 –0.5 –1.0 –1.5 95 90 50.0 85 49.5 IVCC (μA) SWITCHING FREQUENCY (kHz) OUTPUT VOLTAGE CHANGE (%) Quiescent Current–Not Switching Minimum Switching Frequency 2.0 49.0 48.
PAGE 5
LT3494/LT3494A TYPICAL PERFORMANCE CHARACTERISTICS LT3494A Switching Waveforms at No Load LT3494A Switching Waveforms at 5mA Load FIGURE 6 CIRCUIT FIGURE 6 CIRCUIT VOUT 10mV/DIV AC COUPLED VOUT 10mV/DIV AC COUPLED SW VOLTAGE 10V/DIV SW VOLTAGE 10V/DIV INDUCTOR CURRENT 50mA/DIV INDUCTOR CURRENT 100mA/DIV VCC = 3.6V VOUT = 16V 5ms/DIV TA = 25°C unless otherwise noted. 3494 G13 VOUT VOLTAGE 50mV/DIV AC COUPLED 2ms/DIV 3494 G14 VCC = 3.6V VOUT = 16V 200μs/DIV 3494 G16 VCC = 3.
PAGE 6
LT3494/LT3494A PIN FUNCTIONS SW (Pin 1): Switch Pin. This is the collector of the internal NPN power switch. Minimize the metal trace area connected to this pin to minimize EMI. GND (Pin 2): Ground. Tie directly to local ground plane. FB (Pin 6): Feedback Pin. Reference voltage is 1.225V. There is an internal 182k resistor from the FB pin to GND. To achieve the desired output voltage, choose R1 according to the following formula: ⎛ VOUT(MAX ) ⎞ R1 = 182 • ⎜ – 1⎟ kΩ ⎝ 1.
PAGE 7
LT3494/LT3494A OPERATION The LT3494/LT3494A use a novel control scheme to provide high efﬁciency over a wide range of output current. In addition, this technique keeps the switching frequency above the audio band over all load conditions. The operation of the part can be better understood by refering to the Block Diagram. The part senses the output voltage by monitoring the voltage on the FB pin. The user sets the desired output voltage by choosing the value of the external top feedback resistor.
PAGE 8
LT3494/LT3494A APPLICATIONS INFORMATION 1.500 The small size and low ESR of ceramic capacitors makes them suitable for most LT3494/LT3494A applications. X5R and X7R types are recommended because they retain their capacitance over wider voltage and temperature ranges than other types such as Y5V or Z5U. A 4.7μF input capacitor and a 2.2μF to 10μF output capacitor are sufﬁcient for most LT3494/LT3494A applications. Always use a capacitor with a sufﬁcient voltage rating. Many capacitors rated at 2.
PAGE 9
LT3494/LT3494A APPLICATIONS INFORMATION Connecting the Load to the CAP Node The efﬁciency of the converter can be improved by connecting the load to the CAP pin instead of the VOUT pin. The power loss in the PMOS disconnect circuit is then made negligible. By connecting the feedback resistor to the VOUT pin, no quiescent current will be consumed in the feedback resistor string during shutdown since the PMOS transistor will be open (see Figure 3).
PAGE 10
LT3494/LT3494A APPLICATIONS INFORMATION the CAP pin will improve efﬁciency and lower the stress placed on the internal Schottky diode. GND Board Layout Considerations SW As with all switching regulators, careful attention must be paid to the PCB board layout and component placement. To maximize efﬁciency, switch rise and fall times are made as short as possible. To prevent electromagnetic interference (EMI) problems, proper layout of the high frequency switching path is essential.
PAGE 11
LT3494/LT3494A PACKAGE DESCRIPTION DDB Package 8-Lead Plastic DFN (3mm × 2mm) (Reference LTC DWG # 05-08-1702 Rev B) 0.61 ±0.05 (2 SIDES) 0.70 ±0.05 2.55 ±0.05 1.15 ±0.05 PACKAGE OUTLINE 0.25 ± 0.05 0.50 BSC 2.20 ±0.05 (2 SIDES) RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS 3.00 ±0.10 (2 SIDES) R = 0.115 TYP 5 R = 0.05 TYP 0.40 ± 0.10 8 2.00 ±0.10 (2 SIDES) PIN 1 BAR TOP MARK (SEE NOTE 6) 0.56 ± 0.05 (2 SIDES) 0.200 REF 0.75 ±0.05 0 – 0.05 4 0.25 ± 0.05 1 PIN 1 R = 0.20 OR 0.
PAGE 12
LT3494/LT3494A TYPICAL APPLICATION L1 10μH VIN 3V TO 4.2V Efficiency and Power Loss vs Load Current D1 80 3 8 SW CAP VCC VOUT 7 LT3494A 5 4 SHDN FB CTRL GND 6 75 70 VOUT R1 300 LOAD FROM CAPACITOR C1 0.47μF C3 10μF 2 3494 F06 C1, C2: X5R OR X7R WITH SUFFICIENT VOLTAGE RATING C3: TAIYO YUDEN TMK316BJ106ML D1: CENTRAL SEMICONDUCTOR CMDSH-3 L1: MURATA LQH32CN100K53 200 65 150 60 55 100 50 50 45 40 0.1 Figure 6. One Li-Ion Cell Input Boost Converter with the LT3494A VIN = 3.