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LTC3409

3409fc

FEATURES DESCRIPTION

■

Cellular Phones

■

Digital Cameras

■

MP3 Players

High Efﬁ ciency Step-Down Converter

600mA Low V

Buck

Regulator in 3mm × 3mm DFN

■

1.6V to 5.5V Input Voltage Range

■

Internal Soft-Start

■

Selectable 1.7MHz or 2.6MHz Constant Frequency

Operation

■

Internal Oscillator can be Synchronizable to an

External Clock, 1MHz to 3MHz Range

■

High Efﬁ ciency: Up to 95%

■

Very Low Quiescent Current: Only 65μA During

Burst Mode

Operation

■

600mA Output Current (V

= 1.8V, V

OUT

= 1.2V)

■

750mA Peak Inductor Current

■

No Schottky Diode Required

■

Low Dropout Operation: 100% Duty Cycle

■

0.613V Reference Voltage

■

Stable with Ceramic Capacitors

■

Shutdown Mode Draws <1μA Supply Current

■

Current Mode Operation for Excellent Line and Load

Transient Response

■

Overtemperature Protection

■

Available in a Low Proﬁ le (0.75mm) 8-Lead

(3mm × 3mm) DFN Package

Burst Mode Efﬁ ciency, 1.8V

OUT

The LTC

3409 is a high efﬁ ciency, monolithic synchronous

buck regulator using a constant frequency, current mode

architecture. The output voltage is adjusted via an external

resistor divider.

Fixed switching frequencies of 1.7MHz and 2.6MHz are

supported. Alternatively, an internal PLL will synchronize

to an external clock in the frequency range of 1MHz to

3MHz. This range of switching frequencies allows the

use of small surface mount inductors and capacitors,

including ceramics.

Supply current during Burst Mode operation is only

65μA dropping to <1μA in shutdown. The 1.6V to 5.5V

input voltage range makes the LTC3409 ideally suited

for single cell Li-Ion, Li-Metal and 2-cell alkaline, NiCd

or NiMH battery-powered applications. 100% duty cycle

capability provides low dropout operation, extending bat-

tery life in portable systems. Burst Mode operation can be

user-enabled, increasing efﬁ ciency at light loads, further

extending battery life.

The internal synchronous switch increases efﬁ ciency and

eliminates the need for an external Schottky diode. Internal

soft-start offers controlled output voltage rise time at start-

up without the need for external components.

RUN

MODE

SYNC

GND

LTC3409

2.2μH*

OUT

1.8V

255k

4.7μF

CER

1.8V TO 5.5V

133k

*SUMIDA CDRH2D18/LD

3409 TA01

10pF

10μF

CER

, LT, LTC, LTM and Burst Mode are registered trademarks of Linear Technology

Corporation. All other trademarks are the property of their respective owners.

Protected by U.S. Patents, including 5481178, 6580258, 6304066, 6127815,

6498466, 6611131.

LOAD CURRENT (mA)

EFFICIENCY (%)

POWER LOSS (W)

100

0.1 10 100 1000

3409 TA01b

1.0

0.1

0.01

0.001

0.0001

2.5V

, BURST

4.2V

, BURST

3.6V

, BURST

POWER LOST

3.6V

, BURST

APPLICATIONS

TYPICAL APPLICATION

Summary of content (16 pages)

PAGE 1
LTC3409 600mA Low VIN Buck Regulator in 3mm × 3mm DFN FEATURES ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ DESCRIPTION The LTC®3409 is a high efﬁciency, monolithic synchronous buck regulator using a constant frequency, current mode architecture. The output voltage is adjusted via an external resistor divider. 1.6V to 5.5V Input Voltage Range Internal Soft-Start Selectable 1.7MHz or 2.
PAGE 2
LTC3409 ABSOLUTE MAXIMUM RATINGS PIN CONFIGURATION (Note 1) TOP VIEW Input Supply Voltage ................................... – 0.3V to 6V RUN, VFB, MODE, SYNC Voltages . – 0.3V to (VIN + 0.3V) SW Voltage ................................... – 0.3V to (VIN + 0.3V) Operating Temperature Range (Note 2) .. –40°C to 85°C Junction Temperature (Note 3) ........................... 125°C Storage Temperature Range..................
PAGE 3
LTC3409 ELECTRICAL CHARACTERISTICS The ● denotes speciﬁcations which apply over the full operating temperature range, otherwise speciﬁcations are TA = 25°C. VIN = 2.2V unless otherwise speciﬁed. SYMBOL PARAMETER CONDITIONS IS Input DC Bias Current Active Mode Sleep Mode Shutdown (Note 5) VOUT = 90%, ILOAD = 0A VOUT = 103%, ILOAD = 0A VRUN = 0V, VIN = 5.
PAGE 4
LTC3409 TYPICAL PERFORMANCE CHARACTERISTICS (From Typical Application on the front page except for the resistive divider resistor values) Efﬁciency/Power Lost vs Load Current, VOUT = 1.8V Efﬁciency vs Input Voltage VOUT = 1.2V, Burst Mode Operation 100 100 90 1 90 90 80 2 80 80 70 3 70 70 1.0 60 8 0.01 10 40 7 12 30 50 40 30 0.001 11 20 60 20 9 10 1 10 100 LOAD CURRENT (mA) 1: 2.5VIN, BURST 2: 3.6VIN, BURST 3: 4.2VIN, BURST 4: 2.5VIN, PULSE SKIP 5: 3.6VIN, PULSE SKIP 6: 4.
PAGE 5
LTC3409 TYPICAL PERFORMANCE CHARACTERISTICS (From Typical Application on the front page except for the resistive divider resistor values) Oscillator Frequency vs Temperature Output Voltage vs Load Current VIN = 1.6V 6 OSCILLATOR FREQUENCY SHIFT (%) VIN = 2.7V VIN = 1.6V VIN = 4.2V OSC 1.7MHz VIN = 4.2V VIN = 1.6V –25 OSC 2.6MHz VIN = 2.7V 50 25 75 0 TEMPERATURE (°C) 100 1.22 4 fLOW 1.7MHz 2 0 fHIGH 2.6MHz –2 –4 –6 2.5 3.5 DYNAMIC SUPPLY CURRENT, PULSE SKIP (μA) 0.50 MAIN SWITCH 1.
PAGE 6
LTC3409 TYPICAL PERFORMANCE CHARACTERISTICS (From Typical Application on the front page except for the resistive divider resistor values) Load Step 0mA to 600mA Pulse Skip Start-Up from Shutdown RUN 2V/DIV VOUT 100mV/DIV VOUT 1V/DIV ILOAD 500mA/DIV INDUCTOR CURRENT 500mA/DIV INDUCTOR CURRENT 500mA/DIV 200μs/DIV 3409 G16 20μs/DIV 3409 G17 Burst Mode Operation ILOAD = 35mA Load Step 50mA to 600mA Pulse Skip VOUT 20mV/DIV VOUT 100mV/DIV VSWITCH 2V/DIV ILOAD 500mA/DIV INDUCTOR CURRENT 200mA/DIV I
PAGE 7
LTC3409 PIN FUNCTIONS VFB (Pin 1): Feedback Pin. Receives the feedback voltage from an external resistive divider across the output. GND (Pin 2): Ground Pin. VIN (Pins 3, 4): Main Supply Pins. Must be closely decoupled to GND, Pin 2 and Pin 9, with a 4.7μF or greater ceramic capacitor. SYNC (Pin 8): External CLK Input/Fixed Switching Frequency Selection. Forcing this pin above 1.1V for greater than 30μs selects 2.6MHz switching frequency. Forcing this pin below 0.3V for greater than 30μs selects 1.
PAGE 8
LTC3409 FUNCTIONAL DIAGRAM MODE 5 SLOPE COMP SYNC 8 0.65V PLL OSC VIN – VFB 1 0.613V + – 3, 4 + – 0.4V EA EN SLEEP – + BURST SOFTSTART S Q R Q RS LATCH VIN 7 + REFERENCE OVDET 0.675 SWITCHING LOGIC AND BLANKING CIRCUIT ANTISHOOTTHRU 6 SW OV – + RUN 5Ω + ICOMP SHUTDOWN IRCMP 2 GND – 3409 FD OPERATION Main Control Loop The LTC3409 uses a constant frequency, current mode stepdown architecture.
PAGE 9
LTC3409 OPERATION to audio circuitry. When the converter is in Burst Mode operation, the minimum peak current of the inductor is set to approximately 200mA regardless of the output load. Each burst event can last from a few cycles at light loads to almost continuously cycling with short sleep intervals at moderate loads. In between these burst events, the power MOSFETs and any unneeded circuitry are turned off, reducing the quiescent current to 65μA.
PAGE 10
LTC3409 APPLICATIONS INFORMATION The basic LTC3409 application circuit is shown on the ﬁrst page of this data sheet. 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 VALUE (μH) DCR (Ω MAX) MAX DC CURRENT (A) SIZE W × L × H (mm3) Sumida CDRH2D18/LD 2.2 3.3 0.041 0.054 0.85 0.75 3.2 × 3.2 × 2.0 Inductor Selection Sumida CDRH2D11 1.5 2.2 0.068 0.170 0.90 0.78 3.2 × 3.2 × 1.
PAGE 11
LTC3409 APPLICATIONS INFORMATION where f = operating frequency, COUT = output capacitance and ΔIL = ripple current in the inductor. For a ﬁxed output voltage, the output ripple is highest at maximum input voltage since ΔIL 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 12
LTC3409 APPLICATIONS INFORMATION 1 Other losses including CIN and COUT ESR dissipative losses and inductor core losses generally account for less than 2% total additional loss. BURST PULSE SKIP POWER LOSS (W) 0.1 0.01 0.001 Thermal Considerations 2.5VIN 3.6VIN 4.2VIN 4.2VIN 3.6VIN 0.0001 0.1 2.5VIN 1 10 100 LOAD CURRENT (mA) 1000 3409 F02 Figure 2 1.
PAGE 13
LTC3409 APPLICATIONS INFORMATION Note that at higher supply voltages, the junction temperature is lower due to reduced switch resistance (RDS(ON)). 2. Are the COUT and L1 closely connected? The (–) plate of COUT returns current to GND and the (–) plate of CIN. Checking Transient Response 3. The resistor divider, R1 and R2, must be connected between the (+) plate of COUT and a ground sense line terminated near GND (Exposed Pad).
PAGE 14
LTC3409 APPLICATIONS INFORMATION Design Example As a design example, assume the LTC3409 is used in a 2-alkaline cell battery-powered application. The VIN will be operating from a maximum of 3.2V down to about 1.8V. The load current requirement is a maximum of 600mA but most of the time it will be in standby mode, requiring only 2mA. Efﬁciency at both low and high load currents is important. Output voltage is 1.5V.
PAGE 15
LTC3409 PACKAGE DESCRIPTION DD Package 8-Lead Plastic DFN (3mm × 3mm) (Reference LTC DWG # 05-08-1698) 0.675 ±0.05 3.5 ±0.05 1.65 ±0.05 2.15 ±0.05 (2 SIDES) PACKAGE OUTLINE 0.25 ± 0.05 0.50 BSC 2.38 ±0.05 (2 SIDES) RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS 3.00 ±0.10 (4 SIDES) R = 0.115 TYP 5 0.38 ± 0.10 8 1.65 ± 0.10 (2 SIDES) PIN 1 TOP MARK (NOTE 6) (DD8) DFN 1203 0.200 REF 0.75 ±0.05 0.00 – 0.05 4 0.25 ± 0.05 1 0.50 BSC 2.38 ±0.10 (2 SIDES) BOTTOM VIEW—EXPOSED PAD NOTE: 1.
PAGE 16
LTC3409 TYPICAL APPLICATION 2-Cell to 1.2V/600mA Regulator for High Efﬁciency and Low Proﬁle 3, 4 VIN 1.8V TO 3V CIN 4.7μF CER 7 5 8 LTC3409 6 SW VIN 2.2μH* 22pF RUN MODE VFB 1 301k SYNC GND 9 287k SGND 2 3409 TA02a CIN: TDK C1608X5R0J475M COUT: TDK C1608X5R0G106M *SUMIDA CDRH2D09NP-2R2NC Efﬁciency Load Step 95 VIN = 1.8V 90 VOUT = 1.2V EFFICIENCY (%) 85 VOUT COUT 1.2V 10μF CER VOUT 100mV/DIV AC-COUPLED f = 1.7MHz IL 500mA/DIV f = 2.6MHz 80 ILOAD 500mA/DIV 75 70 20μs/DIV VIN = 1.