Datasheet

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LTC34 06B-2

sn3406b2 3406b2fs

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High Efficiency: Up to 96%

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600mA Output Current at V

= 3V

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2.5V to 5.5V Input Voltage Range

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2.25MHz Constant Frequency Operation

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No Schottky Diode Required

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Low Dropout Operation: 100% Duty Cycle

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Low Quiescent Current: 350µA

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0.6V Reference Allows Low Output Voltages

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Shutdown Mode Draws <1µA Supply Current

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Current Mode Operation for Excellent Line and

Load Transient Response

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Overtemperature Protected

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Low Profile (1mm) SOT-23 Package

The LTC

3406B-2 is a high efficiency monolithic synchro-

nous buck regulator using a constant frequency, current

mode architecture. Supply current with no load is 350µA,

dropping to <1µA in shutdown. The 2.5V to 5.5V input

voltage range makes the LTC3406B-2 ideally suited for

single Li-Ion battery-powered applications. 100% duty

cycle capability provides low dropout operation, extend-

ing battery life in portable systems. PWM pulse skipping

mode operation provides very low output ripple voltage for

noise sensitive applications.

The switching frequency is internally set at 2.25MHz, allow-

ing the use of tiny surface mount inductors and capacitors.

The internal synchronous switch increases efficiency and

eliminates the need for an external Schottky diode. Low

output voltages are easily supported with the 0.6V feedback

reference voltage. The LTC3406B-2 is available in a low pro-

file (1mm) SOT-23 package. Refer to LTC3406 for appli-

cations that require Burst Mode

operation.

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Cellular Telephones

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Personal Information Appliances

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Wireless and DSL Modems

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Digital Still Cameras

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MP3 Players

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Portable Instruments

2.25MHz, 600mA

Synchronous Step-Down

Regulator in ThinSOT

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

Burst Mode is a registered trademark of Linear Technology Corporation.

ThinSOT is a trademark of Linear Technology Corporation.

Protected by U.S. Patents, including 6580258, 5481178.

FEATURES

APPLICATIO S

TYPICAL APPLICATIO

DESCRIPTIO

High Efficiency Step-Down Converter Efficiency vs Load Current

4.7µF

CER

2.7V

TO 5.5V

LTC3406B-2

RUN

2.2µH*

3406B TA01a

GND

10µF

CER

OUT

1.8V

600mA

22pF

499k

OUTPUT CURRENT (mA)

0.1

EFFICIENCY (%)

1000

100

3406B TA01b

1 100

= 2.7V

OUT

= 1.8V

= 25°C

= 3.6V

= 4.2V

Summary of content (16 pages)

PAGE 1
LTC3406B-2 2.25MHz, 600mA Synchronous Step-Down Regulator in ThinSOTTM U FEATURES ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ DESCRIPTIO The LTC ®3406B-2 is a high efficiency monolithic synchronous buck regulator using a constant frequency, current mode architecture. Supply current with no load is 350µA, dropping to <1µA in shutdown. The 2.5V to 5.5V input voltage range makes the LTC3406B-2 ideally suited for single Li-Ion battery-powered applications.
PAGE 2
LTC3406B-2 W W W AXI U U ABSOLUTE RATI GS U U W PACKAGE/ORDER I FOR ATIO (Note 1) Input Supply Voltage .................................. – 0.3V to 6V RUN, VFB Voltages ..................................... – 0.3V to VIN SW Voltage (DC) ......................... – 0.3V to (VIN + 0.3V) P-Channel Switch Source Current (DC) ............. 800mA N-Channel Switch Sink Current (DC) ................. 800mA Peak SW Sink and Source Current ........................ 1.3A Operating Temperature Range (Note 2) ..
PAGE 3
LTC3406B-2 U W TYPICAL PERFOR A CE CHARACTERISTICS (From Figure 1a Except for the Resistive Divider Resistor Values) Efficiency vs Input Voltage TA = 25°C IOUT = 100mA IOUT = 600mA 80 IOUT = 10mA 75 70 65 3 2 VOUT = 1.5V 90 TA = 25°C 80 80 EFFICIENCY (%) EFFICIENCY (%) 85 100 VOUT = 1.2V TA = 25°C 90 95 90 5 4 INPUT VOLTAGE (V) 70 VIN = 3.6V 60 VIN = 2.7V 50 VIN = 4.2V 40 VIN = 4.2V 40 20 10 0.1 1000 3406B G03 Reference Voltage vs Temperature Oscillator Frequency vs Temperature 0.
PAGE 4
LTC3406B-2 U W TYPICAL PERFOR A CE CHARACTERISTICS (From Figure 1a Except for the Resistive Divider Resistor Values) Dynamic Supply Current vs Supply Voltage RDS(ON) vs Temperature 0.7 390 450 VIN = 4.2V VIN = 3.6V 0.5 0.4 0.3 0.2 0.1 50 25 75 0 TEMPERATURE (°C) 390 370 350 330 310 290 270 MAIN SWITCH SYNCHRONOUS SWITCH 0 –50 –25 VOUT = 1.8V 430 ILOAD = 0A TA = 25°C 410 DYNAMIC SUPPLY CURRENT (µA) 0.6 DYNAMIC SUPPLY CURRENT (µA) VIN = 2.
PAGE 5
LTC3406B-2 U W TYPICAL PERFOR A CE CHARACTERISTICS (From Figure 1a Except for the Resistive Divider Resistor Values) Load Step Load Step VOUT 100mV/DIV AC COUPLED VOUT 100mV/DIV AC COUPLED IL 500mA/DIV IL 500mA/DIV ILOAD 500mA/DIV ILOAD 500mA/DIV VIN = 3.6V 20µs/DIV VOUT = 1.8V ILOAD = 100mA TO 600mA 3406B G19 VIN = 3.6V 20µs/DIV VOUT = 1.8V ILOAD = 200mA TO 600mA 3406B G20 U U U PI FU CTIO S RUN (Pin 1): Run Control Input. Forcing this pin above 1.5V enables the part.
PAGE 6
LTC3406B-2 W FU CTIO AL DIAGRA U U SLOPE COMP OSC 4 VIN OSC FREQ SHIFT – – 5Ω + ICOMP + 0.6V VFB + – EA 5 Q R Q RS LATCH VIN – OVDET RUN 0.65V OV SWITCHING LOGIC AND BLANKING CIRCUIT ANTISHOOTTHRU 3 SW + 0.6V REF SHUTDOWN + 1 S IRCMP 2 GND – 3406B BD U OPERATIO (Refer to Functional Diagram) Main Control Loop The LTC3406B-2 uses a constant frequency, current mode step-down architecture.
PAGE 7
LTC3406B-2 U OPERATIO (Refer to Functional Diagram) frequency. This frequency foldback ensures that the inductor current has more time to decay, thereby preventing runaway. The oscillator’s frequency will progressively increase to 2.25MHz when VFB rises above 0V. Dropout Operation As the input supply voltage decreases to a value approaching the output voltage, the duty cycle increases toward the maximum on-time.
PAGE 8
LTC3406B-2 U W U U APPLICATIO S I FOR ATIO The basic LTC3406B-2 application circuit is shown in Figure 1. External component selection is driven by the load requirement and begins with the selection of L followed by CIN and COUT. Table 1. Representative Surface Mount Inductors Part Number Value (µH) DCR (ΩMAX) MAX DC Current (A) Size WxLxH (mm3) Sumida CDRH2D11 1.5 2.2 3.3 0.068 0.098 0.123 0.90 0.78 0.60 3.2 x 3.2 x 1.2 Sumida CDRH2D18/LD 2.2 3.3 4.7 0.041 0.054 0.078 0.85 0.75 0.63 3.
PAGE 9
LTC3406B-2 U W U U APPLICATIO S I FOR ATIO Using Ceramic Input and Output Capacitors Higher values, lower cost ceramic capacitors are now becoming available in smaller case sizes. Their high ripple current, high voltage rating and low ESR make them ideal for switching regulator applications. Because the LTC3406B-2’s control loop does not depend on the output capacitor’s ESR for stable operation, ceramic capacitors can be used freely to achieve very low output ripple and small circuit size.
PAGE 10
LTC3406B-2 U W U U APPLICATIO S I FOR ATIO 1. The VIN quiescent current is due to two components: the DC bias current as given in the electrical characteristics and the internal main switch and synchronous switch gate charge currents. The gate charge current results from switching the gate capacitance of the internal power MOSFET switches. Each time the gate is switched from high to low to high again, a packet of charge, dQ, moves from VIN to ground.
PAGE 11
LTC3406B-2 U W U U APPLICATIO S I FOR ATIO A second, more severe transient is caused by switching in loads with large (>1µF) supply bypass capacitors. The discharged bypass capacitors are effectively put in parallel with COUT, causing a rapid drop in VOUT. No regulator can deliver enough current to prevent this problem if the load switch resistance is low and it is driven quickly.
PAGE 12
LTC3406B-2 U W U U APPLICATIO S I FOR ATIO Design Example A 2.2µH inductor works well for this application. For best efficiency choose a 720mA or greater inductor with less than 0.2Ω series resistance. CIN will require an RMS current rating of at least 0.3A ≅ ILOAD(MAX)/2 at temperature and COUT will require an ESR of less than 0.25Ω. In most cases, a ceramic capacitor will satisfy this requirement.
PAGE 13
LTC3406B-2 U TYPICAL APPLICATIO S Single Li-Ion 1.2V/600mA Regulator for High Efficiency and Small Footprint VIN 2.7V TO 4.2V 4 CIN† 4.7µF CER VIN SW 3 2.2µH* 22pF VFB RUN GND 2 VOUT 1.2V COUT** 10µF CER LTC3406B-2 1 Load Step 5 301k VOUT 100mV/DIV AC COUPLED IL 500mA/DIV 301k 3406B TA09 *MURATA LQH32CN2R2M33 ** TAIYO YUDEN JHK316BJ106ML † TAIYO YUDEN JMK212BJ475MG ILOAD 500mA/DIV VIN = 3.6V 20µs/DIV VOUT = 1.2V ILOAD = 0mA TO 600mA Efficiency vs Output Current 100 90 Load Step VOUT = 1.
PAGE 14
LTC3406B-2 U TYPICAL APPLICATIO S 5V Input to 3.3V/0.6A Regulator 4 VIN 5V † CIN 4.7µF CER VIN SW 3 2.2µH* VOUT 3.3V 22pF COUT** 10µF CER LTC3406B-2 1 RUN VFB GND 2 Load Step 5 VOUT 100mV/DIV AC COUPLED IL 500mA/DIV 1M 221k ILOAD 500mA/DIV 3406B TA13 *MURATA LQH32CN2R2M33 ** TAIYO YUDEN JHK316BJ106ML † TAIYO YUDEN JMK212BJ475MG VIN = 3.6V 20µs/DIV VOUT = 3.3V ILOAD = 0mA TO 600mA Efficiency vs Output Current 100 90 Load Step VOUT = 3.
PAGE 15
LTC3406B-2 U PACKAGE DESCRIPTIO S5 Package 5-Lead Plastic TSOT-23 (Reference LTC DWG # 05-08-1635) 0.62 MAX 0.95 REF 2.90 BSC (NOTE 4) 1.22 REF 1.4 MIN 3.85 MAX 2.62 REF 2.80 BSC 1.50 – 1.75 (NOTE 4) PIN ONE RECOMMENDED SOLDER PAD LAYOUT PER IPC CALCULATOR 0.30 – 0.45 TYP 5 PLCS (NOTE 3) 0.95 BSC 0.80 – 0.90 0.20 BSC 0.01 – 0.10 1.00 MAX DATUM ‘A’ 0.30 – 0.50 REF 0.09 – 0.20 (NOTE 3) NOTE: 1. DIMENSIONS ARE IN MILLIMETERS 2. DRAWING NOT TO SCALE 3. DIMENSIONS ARE INCLUSIVE OF PLATING 4.
PAGE 16
LTC3406B-2 RELATED PARTS PART NUMBER DESCRIPTION COMMENTS LT1616 500mA (IOUT), 1.4MHz, High Efficiency Step-Down DC/DC Converter 90% Efficiency, VIN: 3.6V to 25V, VOUT(MIN) = 1.25V, IQ = 1.9mA, ISD < 1µA, ThinSOT Package LT1676 450mA (IOUT), 100kHz, High Efficiency Step-Down DC/DC Converter 90% Efficiency, VIN: 7.4V to 60V, VOUT(MIN) = 1.24V, IQ = 3.2mA, ISD = 2.5µA, S8 Package LTC1877 600mA (IOUT), 550kHz, Synchronous Step-Down DC/DC Converter 95% Efficiency, VIN: 2.7V to 10V, VOUT(MIN) = 0.