Datasheet

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LTC3406A

3406afa

TYPICAL APPLICATION

FEATURES

APPLICATIONS

DESCRIPTION

1.5MHz, 600mA

Synchronous Step-Down

Regulator in ThinSOT

The LTC

3406A is a high efﬁ ciency monolithic synchro-

nous buck regulator using a constant frequency, current

mode architecture. Supply current during operation is only

20μA, dropping to ≤1μA in shutdown. The 2.5V to 5.5V

input voltage range makes the LTC3406A ideally suited

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

cycle provides low dropout operation, extending battery

runtime portable systems. Automatic Burst Mode opera-

tion increases efﬁ ciency at light loads, further extending

battery runtime.

Switching frequency is internally set at 1.5MHz, allowing

the use of small surface mount inductors and capacitors.

The internal synchronous switch increases efﬁ ciency

and eliminates the need for an external Schottky diode.

Low output voltages are easily supported with the 0.6V

feedback reference voltage. The LTC3406A is available in

a low proﬁ le (1mm) ThinSOT package.

Efﬁ ciency vs Load Current

■

High Efﬁ ciency: Up to 96%

■

Very Low Quiescent Current: Only 20µA

■

Low Output Ripple Voltage During Burst Mode

Operation

■

600mA Output Current

■

2.5V to 5.5V Input Voltage Range

■

1.5MHz Constant Frequency Operation

■

No Schottky Diode Required

■

Low Dropout Operation: 100% Duty Cycle

■

±2%

0.6V Reference

■

Shutdown Mode Draw ≤1µA Supply Current

■

Internal Soft-Start Limits Inrush Current

■

Current Mode Operation for Excellent Line and

Load Transient Response

■

Overtemperature Protected

■

Low Proﬁ le (1mm) ThinSOT

Package

■

Cellular Telephones

■

Wireless and DSL Modems

■

Digital Still Cameras

■

Media Players

■

Portable Instruments

■

Point of Load Regulation

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

ThinSOT is a registered trademark of Linear Technology Corporation.

All other trademarks are the property of their respective owners.

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

4.7μF

CER

LTC3406A

RUN

2.2μH

22pF

619k

309k

3406A TA01

GND

10μF

CER

OUT

1.8V

600mA

OUTPUT CURRENT (mA)

EFFICIENCY (%)

100

0.1 10 100 1000

3406A TA01b

= 2.7V

= 3.6V

= 4.2V

OUT

= 1.8V

Summary of content (16 pages)

PAGE 1
LTC3406A 1.5MHz, 600mA Synchronous Step-Down Regulator in ThinSOT DESCRIPTION FEATURES ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ High Efficiency: Up to 96% Very Low Quiescent Current: Only 20µA Low Output Ripple Voltage During Burst Mode® Operation 600mA Output Current 2.5V to 5.5V Input Voltage Range 1.5MHz Constant Frequency Operation No Schottky Diode Required Low Dropout Operation: 100% Duty Cycle ±2% 0.
PAGE 2
LTC3406A ABSOLUTE MAXIMUM RATINGS PIN CONFIGURATION (Note 1) TOP VIEW 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) (Note 7)................................................................800mA N-Channel Switch Sink Current (DC) (Note 7) .....800mA Peak SW Sink and Source Current (Note 7) .............1.
PAGE 3
LTC3406A ELECTRICAL CHARACTERISTICS The ● denotes the speciﬁcations which apply over the full operating temperature range, otherwise speciﬁcations are at TA = 25°C. VIN = 3.6V unless otherwise speciﬁed. SYMBOL PARAMETER CONDITIONS TYP MAX UNITS RNFET RDS(ON) of N-Channel FET ISW = –100mA 0.21 0.35 Ω ILSW SW Leakage VRUN = 0V, VSW = 0V or 5V, VIN = 5V ±0.01 ±1 μA tSOFT-START Soft-Start Time VFB from 10% to 90% Full-Scale 0.6 0.9 1.2 ms VRUN RUN Threshold ● 0.3 1 1.
PAGE 4
LTC3406A TYPICAL PERFORMANCE CHARACTERISTICS (From Front Page Figure Except for the Resistive Divider Resistor Values) VOUT = 1.8V 1.812 0.615 0.610 80 EFFICIENCY (%) 1.808 1.804 1.800 1.796 70 60 50 40 1.792 30 1.788 20 1.784 10 1.780 2 600 400 200 OUTPUT CURRENT (mA) IL = 10mA IL = 100mA IL = 600mA VOUT = 2.5V 0 0 3 4 5 INPUT VOLTAGE (V) Oscillator Frequency vs Temperature 0.595 0.590 0.585 –50 –25 6 1.55 1.50 1.45 1.40 1.35 125 Burst Mode 1.55 SW 2V/DIV 1.50 1.
PAGE 5
LTC3406A TYPICAL PERFORMANCE CHARACTERISTICS (From Front Page Figure Except for the Resistive Divider Resistor Values) Dynamic Supply Current vs Temperature Switch Leakage vs Temperature VIN = 3.6V VOUT = 1.
PAGE 6
LTC3406A PIN FUNCTIONS RUN (Pin 1): Run Control Input. Forcing this pin above 1.5V enables the part. Forcing this pin below 0.3V shuts down the device. In shutdown, all functions are disabled drawing <1μA supply current. Do not leave RUN ﬂoating. VIN (Pin 4): Main Supply Pin. Must be closely decoupled to GND, Pin 2, with a 2.2μF or greater ceramic capacitor. VFB (Pin 5): Feedback Pin. Receives the feedback voltage from an external resistive divider across the output. GND (Pin 2): Ground Pin.
PAGE 7
LTC3406A OPERATION (Refer to Functional Diagram) Main Control Loop The LTC3406A uses a constant frequency, current mode step-down architecture. Both the main (P-channel MOSFET) and synchronous (N-channel MOSFET) switches are internal. During normal operation, the internal top power MOSFET is turned on each cycle when the oscillator sets the RS latch, and turned off when the current comparator, ICOMP, resets the RS latch.
PAGE 8
LTC3406A APPLICATIONS INFORMATION The basic LTC3406A application circuit is shown on the front page. 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 (Ω MAX) MAX DC CURRENT (A) SIZE W × L × H (mm3) Sumida CDRH3D16 1.5 2.2 3.3 4.7 0.043 0.075 0.110 0.162 1.55 1.20 1.10 0.90 3.8 × 3.8 × 1.8 Sumida CMD4D06 2.2 3.3 4.7 0.116 0.174 0.216 0.950 0.
PAGE 9
LTC3406A APPLICATIONS INFORMATION The selection of COUT is driven by the required effective series resistance (ESR). Typically, once the ESR requirement for COUT has been met, the RMS current rating generally far exceeds the IRIPPLE(P-P) requirement. The output ripple ∆VOUT is determined by: 1 VOUT IL ESR + 8fCOUT where f = operating frequency, COUT = output capacitance and ∆IL = ripple current in the inductor.
PAGE 10
LTC3406A APPLICATIONS INFORMATION Although all dissipative elements in the circuit produce losses, two main sources usually account for most of the losses in LTC3406A circuits: VIN quiescent current and I2R losses. The VIN quiescent current loss dominates the efﬁciency loss at very low load currents whereas the I2R loss dominates the efﬁciency loss at medium to high load currents.
PAGE 11
LTC3406A APPLICATIONS INFORMATION The junction temperature, TJ, is given by: TJ = TA + TR where TA is the ambient temperature. As an example, consider the LTC3406A in dropout at an input voltage of 2.7V, a load current of 600mA and an ambient temperature of 70°C. From the typical performance graph of switch resistance, the RDS(ON) of the P-channel switch at 70°C is approximately 0.27Ω. Therefore, power dissipated by the part is: PD = ILOAD2 • RDS(ON) = 97.2mW For the SOT-23 package, the θJA is 250°C/ W.
PAGE 12
LTC3406A APPLICATIONS INFORMATION 1 RUN VFB 5 LTC3406A 2 R2 – COUT VOUT 3 + R1 GND SW L1 VIN CFWD 4 CIN VIN BOLD LINES INDICATE HIGH CURRENT PATHS 3406A F03 Figure 3. LTC3406A Layout Diagram VIA TO VIN CFWD LTC3406A L1 VIA TO VOUT R2 PIN 1 VOUT VIN R1 SW COUT CIN GND 3406A F04 Figure 4. LTC3406A Suggested Layout Design Example As a design example, assume the LTC3406A is used in a single lithium-ion battery-powered cellular phone application.
PAGE 13
LTC3406A APPLICATIONS INFORMATION Figure 5 shows the complete circuit along with its efﬁciency curve. For the feedback resistors, choose R1 = 316k. R2 can then be calculated from Equation (2) to be: V R2 = OUT 1 R1= 1000k 0.6 (4) 4 VIN 2.7V TO 4.2V † CIN 4.7μF CER VIN SW 3 2.2μH* VOUT 2.
PAGE 14
LTC3406A TYPICAL APPLICATIONS Single Li-Ion 1.2V/600mA Regulator for High Efﬁciency and Small Footprint 4 VIN † CIN 4.7μF CER VIN SW 3 2.2μH* 22pF LTC3406A 1 VFB RUN GND 2 5 VOUT 1.2V 600mA COUT** 10μF CER 301k * MURATA LQH32CN2R2M33 ** TAIYO YUDEN JMK316BJ106ML † TAIYO YUDEN JMK212BJ475MG 3406A TA02 301k Efﬁciency vs Load Current Load Step 100 90 VOUT 100mV/DIV EFFICIENCY (%) 80 70 60 IL 500mA/DIV 50 ILOAD 500mA/DIV 40 30 20 10 VOUT = 1.2V 0 0.1 VIN = 2.7V VIN = 3.6V VIN = 4.
PAGE 15
LTC3406A PACKAGE DESCRIPTION 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
LTC3406A RELATED PARTS PART NUMBER DESCRIPTION COMMENTS LTC3406/LTC3406B 600mA (IOUT), 1.5MHz, Synchronous Step-Down DC/DC Converters 96% Efﬁciency, VIN: 2.5V to 5.5V, VOUT(MIN) = 0.6V, IQ = 20μA, ISD <1μA, ThinSOT Package LTC3407/LTC3407-2 Dual 600mA/800mA (IOUT), 1.5MHz/2.25MHz, Synchronous Step-Down DC/DC Converters 95% Efﬁciency, VIN: 2.5V to 5.5V, VOUT(MIN) = 0.6V, IQ = 40μA, ISD <1μA, MS10E, DFN Packages LTC3410/LTC3410B 300mA (IOUT), 2.