Datasheet

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LT3473/LT3473A

3473f

■

OLED Bias

■

CCD Bias

Conversion Efficiency and Power Loss vs Output Current

Micropower 1A Boost

Converter with Schottky

and Output Disconnect

■

Tiny Solution Size

■

Low Quiescent Current:

150µA in Active Mode (V

= 3.6V, V

OUT

= 15V,

No Load)

1µA in Shutdown Mode

■

Internal 1A, 36V Switch

■

Integrated Schottky Diode

■

Integrated PNP Output Disconnect

■

Internal Reference Override Pin

■

PGOOD Pin

■

25V at 80mA from 3.6V Input

■

Auxiliary NPNs for Intermediate

Bias Voltages (LT3473A)

■

Automatic Burst Mode

Operation at Light Load

■

Constant Switching Frequency: 1.2MHz

■

Thermal Shutdown

■

Input Range: 2.2V to 16V

■

Low Profile (3mm × 3mm) DFN Package (LT3473)

■

Low Profile (4mm × 3mm) DFN Package (LT3473A)

FEATURES

DESCRIPTIO

APPLICATIO S

TYPICAL APPLICATIO

The LT

3473/LT3473A are micropower step-up DC/DC

converters with integrated Schottky diode and output

disconnect circuitry in low profile DFN packages. The

small package size, high level of integration and the use of

tiny SMT components yield a solution size of less than

50mm

. The internal 1A switch allows the device to deliver

25V at up to 80mA from a Li-Ion cell, while automatic Burst

Mode operation maintains efficiency at light load. An

auxiliary reference input (CTRL) allows the user to over-

ride the internal 1.25V feedback reference with any lower

value, allowing full control of the output voltage during

operation. A PGOOD pin sinks current when the output

voltage reaches 90% of final value.

The LT3473A includes two NPN transistors for generating

intermediate bias voltages from the output and is offered

in a 12-lead (4mm × 3mm) DFN package. The LT3473

does not include these NPNs and is offered in an 8-lead

(3mm × 3mm) package.

The rugged 36V switch and output disconnect circuitry

allow outputs up to 34V to be easily generated in a simple

boost topology.

2.2µF

OUT

25V

80mA

3473 TA01a

4.7µF

0.47µF

3V TO 4.2V

100k

LT3473

GND

6.8µH

PGOOD

CTRL

SHDN

OUT

CAP

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

Burst Mode is a registered trademark of Linear Technology Corporation.

All other trademarks are the property of their respective owners.

OUTPUT CURRENT (mA)

0.1

EFFICIENCY (%)

POWER LOSS (mW)

3473 TA01b

100

200

100

400

300

500

= 3.6V

OUT

= 15V

Summary of content (12 pages)

PAGE 1
LT3473/LT3473A Micropower 1A Boost Converter with Schottky and Output Disconnect U FEATURES DESCRIPTIO ■ The LT®3473/LT3473A are micropower step-up DC/DC converters with integrated Schottky diode and output disconnect circuitry in low profile DFN packages. The small package size, high level of integration and the use of tiny SMT components yield a solution size of less than 50mm2.
PAGE 2
LT3473/LT3473A W W W AXI U U ABSOLUTE RATI GS (Note 1) VIN Voltage ............................................................. 16V SHDN Voltage .......................................................... 16V SW Voltage ............................................................. 36V PGOOD Voltage ...................................................... 36V CAP Voltage ............................................................ 36V OUT Voltage .........................................................
PAGE 3
LT3473/LT3473A ELECTRICAL CHARACTERISTICS The ● denotes specifications which apply over the full operating temperature range, otherwise specifications are TA = 25°C. VIN = 3V, SHDN = 3V, CTRL = 2V, unless otherwise specified. PARAMETER CONDITIONS Switching Frequency MIN TYP MAX UNITS 0.9 1.2 1.4 MHz 92 Maximum Duty Cycle ● 88 Switch Current Limit ● 1.2 % A Switch VCESAT ISW = 100mA 45 Switch Leakage Current VSW = 5V 0.1 Schottky Forward Drop ID = 100mA 0.
PAGE 4
LT3473/LT3473A U W TYPICAL PERFOR A CE CHARACTERISTICS TA = 25°C unless otherwise noted. Sleep Mode Quiescent Current (Not Switching) Sleep Mode Quiescent Current 100 95 2.5 SHDN = 3V VIN = 3V 100 SHDN = 3V 98 96 94 92 SHDN = 1.5V 0 50 TEMPERATURE (°C) 4 6 8 10 12 INPUT VOLTAGE, VIN (V) 2 0 100 350 300 250 200 150 100 50 400 600 800 1000 SWITCH CURRENT (mA) Schottky I-V Characteristic ISW = 100mA 48 47 46 45 44 43 0 50 900 800 700 600 500 400 300 200 100 0 100 0 TEMPERATURE (°C) 1.
PAGE 5
LT3473/LT3473A U W TYPICAL PERFOR A CE CHARACTERISTICS TA = 25°C unless otherwise noted. SHDN Voltage to Turn-On Disconnect PNP Auxiliary NPN VBE 0.9 1.2 1.0 0.8 0.6 0.4 1.00 0.8 0.95 0.7 0.90 0.6 0.85 NPN VBE (V) 1.4 SHDN VOLTAGE (V) DISCONNECT PNP QUIESCENT CURRENT (µA) Disconnect PNP Quiescent Current 0.80 0.5 0.75 0.4 0.70 0.3 0.65 0.2 0.2 0.60 0.1 0 5 10 15 20 25 30 35 40 CAP VOLTAGE (V) IE = 100µA 0.
PAGE 6
LT3473/LT3473A W BLOCK DIAGRA 4 3 – + + FB CTRL ERROR AMPLIFIER 7 6 VIN SHDN VC gm VREF 1.25V CAP + 1 Q2 ENABLE OUT PNP DRIVER – 2 POWER SECTION + + – – A4 5 SW A1 BTH 100mV 8 – PGOOD + R A2 S Q Q1 DRIVER Q5 – GND Σ A3 RAMP GENERATOR + 9 COMPARATOR 1.2MHz OSCILLATOR 3437 F01 Figure 1. LT3473 Block Diagram 7 8 – + + FB CTRL ERROR AMPLIFIER 11 10 VIN SHDN VC gm + VREF 1.
PAGE 7
LT3473/LT3473A U W U U APPLICATIO S I FOR ATIO Operation The LT3473 combines a current mode, fixed frequency PWM architecture with Burst Mode micropower operation to maintain high efficiency at light loads. Operation can best be understood by referring to the Block Diagram. The reference of the part is determined by the lower of the internal 1.25V bandgap reference and the voltage at the CTRL pin. The error amplifier compares voltage at the FB pin with the reference and generates an error signal VC.
PAGE 8
LT3473/LT3473A U W U U APPLICATIO S I FOR ATIO The LT3473 includes an internal power Schottky diode and a PNP transistor, Q2, for output disconnect. Q2 disconnects the load from the input during shutdown. The part also has a power good indication pin, PGOOD. When the FB voltage reaches within 100mV of the reference voltage, the comparator A4 turns on Q5, sinking current from PGOOD pin. The LT3473 has thermal shutdown feature with threshold at about 145°C. Inductor Selection A 6.
PAGE 9
LT3473/LT3473A U W U U APPLICATIO S I FOR ATIO Inrush Current Setting the Output Voltages The LT3473 has an integrated Schottky power diode. When supply voltage is abruptly applied to the VIN pin while the output capacitor is discharged, the voltage difference between VIN and CAP generates inrush current flowing from the input through the inductor and the internal Schottky diode to charge the output capacitor at the CAP pin. The maximum current the LT3473’s Schottky can sustain is 2A.
PAGE 10
LT3473/LT3473A U W U U APPLICATIO S I FOR ATIO between the OUT pin and ground. A ceramic capacitor with a value of 1µF is a good choice. The voltage drop (PNP VCESAT) can be accounted for by setting the output voltage according to the following formula: ⎛ R2 ⎞ VOUT = VINT – VCESAT = VREF • ⎜ 1 + ⎟ – VCESAT ⎝ R1⎠ connected to the two bases as shown in Figure 5 to generate buffered voltage at the emitters.
PAGE 11
LT3473/LT3473A U PACKAGE DESCRIPTIO DD Package 8-Lead Plastic DFN (3mm × 3mm) (Reference LTC DWG # 05-08-1698) R = 0.115 TYP 5 0.38 ± 0.10 8 0.675 ±0.05 3.5 ±0.05 1.65 ±0.05 2.15 ±0.05 (2 SIDES) 1.65 ± 0.10 (2 SIDES) 3.00 ±0.10 (4 SIDES) PACKAGE OUTLINE PIN 1 TOP MARK (NOTE 6) (DD8) DFN 1203 4 0.25 ± 0.05 0.75 ±0.05 0.200 REF 0.25 ± 0.05 0.50 BSC 2.38 ±0.05 (2 SIDES) 1 0.50 BSC 2.38 ±0.10 (2 SIDES) 0.00 – 0.05 BOTTOM VIEW—EXPOSED PAD RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS NOTE: 1.
PAGE 12
LT3473/LT3473A U TYPICAL APPLICATIO Efficiency OLED Bias 100k PGOOD OUT COUT 2.2µF CTRL L1 6.8µH SW CAP VIN 2M 20k 100nF CINT 0.47µF FB SHDN CIN 4.7µF VIN = 3.6V 75 100k GND 3473 TA02a VOUT = 15V VOUT = 25V LT3473 EFFICIENCY (%) VIN 3V TO 4.