Datasheet

ManualsBrandsLINEAR TECHNOLOGY ManualsPMICsPMIC - DC/DC voltage regulator Holder TSOT 23 6

LTC3405

3405fa

■

High Efficiency: Up to 96%

■

Very Low Quiescent Current: Only 20

During Operation

■

300mA Output Current at V

= 3V

■

2.5V to 5.5V Input Voltage Range

■

1.5MHz Constant Frequency Operation

■

No Schottky Diode Required

■

Low Dropout Operation: 100% Duty Cycle

■

0.8V Reference Allows Low Output Voltages

■

Shutdown Mode Draws <1µA Supply Current

■

±2% Output Voltage Accuracy

■

Current Mode Operation for Excellent Line and

Load Transient Response

■

Overtemperature Protected

■

Low Profile (1mm) ThinSOT

Package

The LTC

3405 is a high efficiency monolithic synchro-

nous buck regulator using a constant frequency, current

mode architecture. Supply current during operation is

only 20µA and drops to <1µA in shutdown. The 2.5V to

5.5V input voltage range makes the LTC3405 ideally suited

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

cycle provides low dropout operation, extending battery

life in portable systems.

Switching frequency is internally set at 1.5MHz, allowing

the use of small 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 0.8V feed-

back reference voltage. The LTC3405 is available in a low

profile (1mm) ThinSOT package.

For new designs, refer to the LTC3405A data sheet. For

fixed 1.5V and 1.8V output versions, refer to the

LTC3405A-1.5/LTC3405A-1.8 data sheet.

■

Cellular Telephones

■

Personal Information Appliances

■

Wireless and DSL Modems

■

Digital Still Cameras

■

MP3 Players

■

Portable Instruments

Figure 1a. High Efficiency Step-Down Converter

1.5MHz, 300mA

Synchronous Step-Down

Regulator in ThinSOT

Figure 1b. Efficiency vs Load Current

†

2.2µF

CER

2.7V

TO 5.5V

†

††

LTC3405

RUN

MODE

4.7µH**

22pF

887k

280k

3405 F01a

OUT

CONNECTED TO V

FOR 2.7V < V

< 3.3V

MURATA LQH3C4R7M34

TAIYO YUDEN LMK212BJ225MG

AVX TPSB336K006R0600

GND

OUT

††

33µF

OUT

3.3V

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

ThinSOT is a trademark of Linear Technology Corporation.

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

OUTPUT CURRENT (mA)

0.1

EFFICIENCY (%)

1000

100

3405 F01b

1 100

= 3.6V

= 4.2V

= 5.5V

APPLICATIO S

FEATURES

TYPICAL APPLICATIO

DESCRIPTIO

Summary of content (16 pages)

PAGE 1
LTC3405 1.5MHz, 300mA Synchronous Step-Down Regulator in ThinSOT U FEATURES DESCRIPTIO ■ The LTC ®3405 is a high efficiency monolithic synchronous buck regulator using a constant frequency, current mode architecture. Supply current during operation is only 20µA and drops to <1µA in shutdown. The 2.5V to 5.5V input voltage range makes the LTC3405 ideally suited for single Li-Ion battery-powered applications. 100% duty cycle provides low dropout operation, extending battery life in portable systems.
PAGE 2
LTC3405 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 MODE, RUN, VFB Voltages ......................... – 0.3V to VIN SW Voltage .................................. – 0.3V to (VIN + 0.3V) P-Channel Switch Source Current (DC) ............. 400mA N-Channel Switch Sink Current (DC) ................. 400mA Peak SW Sink and Source Current .................... 630mA Operating Temperature Range (Note 2) ..
PAGE 3
LTC3405 U W TYPICAL PERFOR A CE CHARACTERISTICS (From Figure1a Except for the Resistive Divider Resistor Values) Efficiency vs Input Voltage 100 100 IOUT = 100mA 80 IOUT = 10mA IOUT = 1mA IOUT = 250mA 80 75 70 65 VIN = 4.2V 60 VIN = 3.6V 50 VIN = 4.2V 40 50 2.5 10 3.5 4.0 4.5 INPUT VOLTAGE (V) 3.0 VIN = 4.2V 70 5.0 5.5 50 VOUT = 1.8V 0 0.1 3405 G02 3405 G04 Oscillator Frequency vs Temperature Reference Voltage vs Temperature 0.814 100 1.70 VIN = 3.6V VIN = 3.6V 60 VIN = 4.
PAGE 4
LTC3405 U W TYPICAL PERFOR A CE CHARACTERISTICS (From Figure 1a Except for the Resistive Divider Resistor Values) RDS(ON) vs Temperature 600 1600 1.0 V = 2.7V IN DYNAMIC SUPPLY CURRENT (µA) VIN = 4.2V VIN = 3.6V 0.8 0.6 0.4 0.2 1400 1200 1000 800 600 PULSE SKIPPING MODE 400 200 SYNCHRONOUS SWITCH MAIN SWITCH 0 –50 –25 50 25 75 0 TEMPERATURE (°C) 100 VOUT = 1.
PAGE 5
LTC3405 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 Load Step VOUT 100mV/DIV AC COUPLED VOUT 100mV/DIV AC COUPLED IL 200mA/DIV IL 200mA/DIV ILOAD 200mA/DIV ILOAD 200mA/DIV VIN = 3.6V 40µs/DIV VOUT = 1.8V ILOAD = 20mA TO 250mA PULSE SKIPPING MODE 3405 G20 IL 200mA/DIV ILOAD 200mA/DIV VIN = 3.6V 40µs/DIV VOUT = 1.8V ILOAD = 20mA TO 250mA Burst Mode OPERATION 3405 G21 VIN = 3.
PAGE 6
LTC3405 W FU CTIO AL DIAGRA U U MODE 6 SLOPE COMP 0.65V OSC OSC 4 VIN FREQ SHIFT – VFB + 5 – + 0.8V 0.4V – EA SLEEP – + S Q R Q RS LATCH RUN – OVDET 0.85V SWITCHING LOGIC AND BLANKING CIRCUIT ANTISHOOTTHRU 3 SW OV + SHUTDOWN + 0.8V REF 5Ω + ICOMP BURST VIN 1 EN IRCMP 2 GND – 3405 BD U OPERATIO (Refer to Functional Diagram) Main Control Loop The LTC3405 uses a constant frequency, current mode step-down architecture.
PAGE 7
LTC3405 U OPERATIO (Refer to Functional Diagram) Comparator OVDET guards against transient overshoots > 6.25% by turning the main switch off and keeping it off until the fault is removed. until it reaches 100% duty cycle. The output voltage will then be determined by the input voltage minus the voltage drop across the P-channel MOSFET and the inductor.
PAGE 8
LTC3405 U W U U APPLICATIO S I FOR ATIO The basic LTC3405 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 MANUFACTURER PART NUMBER MAX DC VALUE CURRENT DCR HEIGHT Taiyo Yuden LB2016T3R3M 3.3µH 280mA 0.2Ω 1.6mm Panasonic ELT5KT4R7M 4.7µH 950mA 0.2Ω 1.2mm Inductor Selection Murata LQH3C4R7M34 4.7µH 450mA 0.
PAGE 9
LTC3405 U W U U APPLICATIO S I FOR ATIO where f = operating frequency, COUT = output capacitance and ∆IL = ripple current in the inductor. For a fixed output voltage, the output ripple is highest at maximum input voltage since ∆IL increases with input voltage. Aluminum electrolytic and dry tantalum capacitors are both available in surface mount configurations. In the case of tantalum, it is critical that the capacitors are surge tested for use in switching power supplies.
PAGE 10
LTC3405 U W U U APPLICATIO S I FOR ATIO In pulse skipping mode, the LTC3405 is stable with a 4.7µF ceramic output capacitor with VIN ≤ 4.2V. For single Li-Ion applications operating in pulse skipping mode, the circuit shown in Figure 6 can be used When choosing the input and output ceramic capacitors, choose the X5R or X7R dielectric formulations. These dielectrics have the best temperature and voltage characteristics of all the ceramics for a given value and size. 4 CIN 2.
PAGE 11
LTC3405 U W U U APPLICATIO S I FOR ATIO top and bottom MOSFET RDS(ON) and the duty cycle (DC) as follows: RSW = (RDS(ON)TOP)(DC) + (RDS(ON)BOT)(1 – DC) The RDS(ON) for both the top and bottom MOSFETs can be obtained from the Typical Performance Charateristics curves. Thus, to obtain I2R losses, simply add RSW to RL and multiply the result by the square of the average output current. ambient temperature of 70°C.
PAGE 12
LTC3405 U W U U APPLICATIO S I FOR ATIO PC Board Layout Checklist 4. Keep the switching node, SW, away from the sensitive VFB node. When laying out the printed circuit board, the following checklist should be used to ensure proper operation of the LTC3405. These items are also illustrated graphically in Figures 9 and 10. Check the following in your layout: Design Example As a design example, assume the LTC3405 is used in a single lithium-ion battery-powered cellular phone application.
PAGE 13
LTC3405 U W U U APPLICATIO S I FOR ATIO Substituting VOUT = 2.5V, VIN = 4.2V, ∆IL = 100mA and f = 1.5MHz in equation (3) gives: L= For the feedback resistors, choose R1 = 412k. R2 can then be calculated from equation (2) to be: ⎛V ⎞ R2 = ⎜ OUT − 1⎟ R1 = 875.5k; use 887k ⎝ 0.8 ⎠ 2.5V ⎛ 2.5V ⎞ ⎜1 − ⎟ ≅ 6.8µH 1.5MHz(100mA) ⎝ 4.2V ⎠ Figure 11 shows the complete circuit along with its efficiency curve. For best efficiency choose a 300mA or greater inductor with less than 0.3Ω series resistance.
PAGE 14
LTC3405 U TYPICAL APPLICATIO S Single Li-Ion to 1.8V/300mA Regulator Using Ceramic and Tantalum Output Capacitors VIN 2.7V TO 4.2V 4 CIN** 2.2µF CER VIN SW 4.7µH* 3 22pF LTC3405 1 RUN 6 MODE VFB 5 COUT1*** + 1µF CER VOUT 1.8V COUT2† 22µF TANT 887k *MURATA LQH3C4R7M34 **TAIYO YUDEN CERAMIC LMK212BJ225MG ***TAIYO YUDEN CERAMIC JMK107BJ105MA † AVX TAJA226M006R 3405 TA02a GND 698k 2 100 VIN = 2.7V VOUT 100mV/DIV AC COUPLED 90 VIN = 4.2V EFFICIENCY (%) 80 VIN = 3.
PAGE 15
LTC3405 U TYPICAL APPLICATIO S Single Li-Ion to 1.8V/300mA Regulator Using All Ceramic Capacitors Optimized for Lowest Profile, ≤ 1.2mm High VIN 2.7V TO 4.2V 4 CIN** 1µF CER VIN SW LTC3405 1 6 4.7µH* 3 22pF 1M COUT** 1µF CER RUN VFB MODE 5 GND 200k 2 VOUT 1.8V COUT** 1µF CER 332k *PANASONIC ELT5KT4R7M **TAIYO YUDEN CERAMIC JMK107BJ105MA 3405 TA04a 100 VIN = 2.7V 90 VOUT 100mV/DIV AC COUPLED EFFICIENCY (%) 80 VIN = 3.6V 70 IL 200mA/DIV VIN = 4.2V 60 50 ILOAD 200mA/DIV 40 30 0.
PAGE 16
LTC3405 U TYPICAL APPLICATIO S Single Li-Ion to 1.8V/300mA Regulator All Ceramic Capacitors with Lowest Parts Count VIN 2.7V TO 4.2V 4 CIN** 2.2µF CER VIN SW LTC3405 1 6 4.7µH* 3 887k 22pF RUN VFB MODE 5 GND 2 698k 3405 TA05a VOUT 1.8V COUT† 4.7µF CER *MURATA LQH3C4R7M34 **TAIYO YUDEN CERAMIC LMK212BJ225MG † TAIYO YUDEN CERAMIC JMK212BJ475MG 100 VIN = 2.7V VOUT 100mV/DIV AC COUPLED 90 VIN = 4.2V EFFICIENCY (%) 80 70 VIN = 3.6V IL 200mA/DIV 60 50 ILOAD 200mA/DIV 40 30 0.