Datasheet

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LTC3411A

3411afc

For more information www.linear.com/LTC3411A

Typical applicaTion

FeaTures

applicaTions

DescripTion

1.25A, 4MHz, Synchronous

Step-Down DC/DC Converter

The LT C

3411A is a constant frequency, synchronous

step-down DC/DC converter. Intended for medium power

applications, it operates from a 2.5V to 5.5V input voltage

range and has a user configurable operating frequency up

to 4MHz, allowing the use of tiny, low cost capacitors and

inductors 1mm or less in height. The output voltage is

adjustable from 0.8V to 5.5V. Internal synchronous power

switches provide high efficiency. The LTC3411A’s current

mode architecture and external compensation allow the

transient response to be optimized over a wide range of

loads and output capacitors.

The LTC3411A can be configured for automatic power

saving Burst Mode operation (I

= 40µA) to reduce gate

charge losses when the load current drops below the level

required for continuous operation. For reduced noise and

RF interference, the SYNC/MODE pin can be configured to

skip pulses or provide forced continuous operation.

To further maximize battery life, the P-channel MOSFET

is turned on continuously in dropout (100% duty cycle).

In shutdown, the device draws <1µA.

Step-Down 2.5V/1.25A Regulator

Uses Tiny Capacitors and Inductor

High Frequency Operation: Up to 4MHz

Low R

DS(ON)

Internal Switches: 0.15Ω

High Efficiency: Up to 96%

Selectable Low Ripple (25mV

P-P

) Burst Mode

Operation: I

= 40µA

Stable with Ceramic Capacitors

Current Mode Operation for Excellent Line

and Load Transient Response

Short-Circuit Protected

Low Dropout Operation: 100% Duty Cycle

Low Shutdown Current: I

≤ 1µA

Output Voltages from 0.8V to 5V

Synchronizable to External Clock

Supports Pre-Biased Outputs

Small 10-Lead 3mm × 3mm DFN or MSOP Package

Notebook Computers

Digital Cameras

Cellular Phones

Handheld Instruments

Board Mounted Power Supplies

SYNC/MODESYNC

LTC3411A

PGOOD

SHDN/R

PGNDSGND

2.2µH

OUT

2.5V

1.25A

2.5V TO 5.5V

887k

22pF

412k

680pF

3411a TA01a

22µF

12.1k

10µF

549k

Efficiency and Power Loss vs Output Current

OUTPUT CURRENT (mA)

0.1 1 10

EFFICIENCY (%)

POWER LOSS (W)

100 1

0.1

0.01

0.001

0.0001

1000100 10000

3411A TA01b

= 2.7V

= 3.6V

= 4.2V

= 1MHz

Burst Mode OPERATION

L, LT, LTC, LTM, Linear Technology, the Linear logo, Burst Mode and OPTI-LOOP are

registered trademarks and Hot Swap and ThinSOT are trademarks of Linear Technology

Corporation. All other trademarks are the property of their respective owners. Protected by U.S.

Patents including 5481178, 6580258, 6498466, 6611131.

Summary of content (22 pages)

PAGE 1
LTC3411A 1.25A, 4MHz, Synchronous Step-Down DC/DC Converter Description Features n n n n n n n n n n n n n n Uses Tiny Capacitors and Inductor High Frequency Operation: Up to 4MHz Low RDS(ON) Internal Switches: 0.
PAGE 2
LTC3411A Absolute Maximum Ratings (Note 1) PVIN, SVIN Voltages ..................................... –0.3V to 6V VFB, ITH, SHDN/RT Voltages .......... –0.3V to (VIN + 0.3V) SYNC/MODE Voltage .................... –0.3V to (VIN + 0.3V) SW Voltage .................................. –0.3V to (VIN + 0.3V) PGOOD Voltage ............................................ –0.3V to 6V Operating Junction Temperature Range (Notes 2, 5, 8)......................................... –40°C to 125°C Storage Temperature Range..
PAGE 3
LTC3411A Electrical Characteristics The l denotes the specifications which apply over the full operating junction temperature range, otherwise specifications are at TA = 25°C, VIN = 3.6V, RT = 125k unless otherwise specified. (Note 2) SYMBOL PARAMETER IS fOSC Input DC Supply Current (Note 4) Active Mode Sleep Mode Shutdown Shutdown Threshold High Active Oscillator Resistor Oscillator Frequency MIN TYP MAX 2.25 Synchronization Frequency RT = 125k (Note 7) (Note 7) 330 40 0.1 VIN – 0.6 125k 2.
PAGE 4
LTC3411A Typical Performance Characteristics TA = 25°C, VIN = 3.6V, fO = 1MHz, unless otherwise noted. Efficiency vs Input Voltage IOUT = 100mA IOUT = 10mA EFFICIENCY (%) 80 IOUT = 1.25A 70 EFFICIENCY (%) 90 IOUT = 1mA 60 50 IOUT = 0.1mA 100 100 90 90 80 80 70 70 60 50 40 30 VIN = 2.7V VIN = 3.6V VIN = 4.2V 20 40 30 2.5 10 VOUT = 1.8V 4.5 4.0 3.5 INPUT VOLTAGE(V) 3.0 VOUT = 1.8V 0 0.1 5.5 5.0 1 10 100 1000 OUTPUT CURRENT (mA) Efficiency vs Output Current 30 20 VOUT = 1.
PAGE 5
LTC3411A Typical Performance Characteristics otherwise noted. Frequency Variation vs VIN RDS(ON) vs Input Voltage 6 RDS(ON) vs Temperature 0.25 0.30 0.20 0.25 0 –2 RDS(ON) (Ω) 2 RDS(ON) (Ω) FREQUENCY VARIATION (%) 4 0.15 0.10 0.20 0.15 0.10 –4 0.05 0.05 MAIN SWITCH SYNCHRONOUS SWITCH –6 –8 2.5 3.0 3.5 4.0 VIN (V) 4.5 5.0 0.0 2.5 5.5 3.0 4.5 4.0 3.5 INPUT VOLTAGE (V) 5.0 Dynamic Supply Current vs Input Voltage 0.0 –50 5.5 PULSE SKIP Burst Mode OPERATION 0.1 0.01 0.001 2.
PAGE 6
LTC3411A Typical Performance Characteristics otherwise noted. Forced Continuous Mode Start-Up from Shutdown SW 2V/DIV VOUT 50mV/DIV AC COUPLED IL 200mA/DIV 2µs/DIV TA = 25°C, VIN = 3.6V fO = 1MHz, unless Start-Up from Shutdown SHDN/RT 2V/DIV SHDN/RT 2V/DIV VOUT 1V/DIV VOUT 1V/DIV IL 1A/DIV IL 1A/DIV 200µs/DIV 3411A G19 VIN = 3.6V VOUT = 1.
PAGE 7
LTC3411A Pin Functions SHDN/RT (Pin 1): Combination Shutdown and Timing Resistor Pin. The oscillator frequency is programmed by connecting a resistor from this pin to ground. Forcing this pin to SVIN causes the device to be shut down. In shutdown all functions are disabled. PGND (Pin 5): Main Power Ground Pin. Connect to the (–) terminal of COUT, and (–) terminal of CIN. PVIN (Pin 6): Main Supply Pin. Must be closely decoupled to PGND. SVIN (Pin 7): The Signal Power Pin.
PAGE 8
LTC3411A Block Diagram SVIN 7 0.8V SGND 3 ITH 10 PVIN VOLTAGE REFERENCE PMOS CURRENT COMPARATOR ITH LIMIT + BCLAMP + 9 – VFB – 0.74V + – ERROR AMPLIFIER VB 6 – + BURST COMPARATOR SLOPE COMPENSATION OSCILLATOR SW 4 + 0.86V LOGIC – + PGOOD 8 NMOS COMPARATOR – – SHDN/RT 1 SYNC/MODE 2 REVERSE COMPARATOR + PGND 5 3411A BD 3411afc 8 For more information www.linear.
PAGE 9
LTC3411A Operation The LTC3411A uses a constant frequency, current mode architecture. The operating frequency is determined by the value of the RT resistor or can be synchronized to an external oscillator. To suit a variety of applications, the selectable MODE pin allows the user to trade-off noise for efficiency. The output voltage is set by an external divider returned to the VFB pin. An error amplifier compares the divided output voltage with the reference voltage of 0.
PAGE 10
LTC3411A Applications Information A general LTC3411A application circuit is shown in Figure 4. External component selection is driven by the load requirement, and begins with the selection of the inductor L1. Once L1 is chosen, CIN and COUT can be selected. Operating Frequency Selection of the operating frequency is a trade-off between efficiency and component size. High frequency operation allows the use of smaller inductor and capacitor values.
PAGE 11
LTC3411A Applications Information shows some typical surface mount inductors that work well in LTC3411A applications. Table 1. Representative Surface Mount Inductors MANUFACTURER PART NUMBER MAX DC VALUE CURRENT Toko A914BYW-1R2M=P3: D52LC 1.2µH A960AW-1R2M=P3: D518LC 1.2µH Coilcraft Sumida DCR HEIGHT 2.15A 44mΩ 2mm 1.8A 46mΩ 1.8mm DB3015C-1068AS-1R0N 1.0µH 2.1A 43mΩ 1.5mm DB3018C-1069AS-1R0N 1.0µH 2.1A 45mΩ 1.8mm DB3020C-1070AS-1R0N 1.0µH 2.1A 47mΩ 2mm A914BYW-2R2M-D52LC 2.2µH 2.
PAGE 12
LTC3411A Applications Information is adequate for filtering. The output ripple (ΔVOUT) is determined by: ⎛ 1 ⎞ ΔVOUT ≈ ΔIL ⎜ESR + ⎟ 8fO COUT ⎠ ⎝ where fO = operating frequency, COUT = output capacitance and ΔIL = ripple current in the inductor. The output ripple is highest at maximum input voltage since ΔIL increases with input voltage. With ΔIL = 0.
PAGE 13
LTC3411A Applications Information In most applications, the input capacitor is merely required to supply high frequency bypassing, since the impedance to the supply is very low. A 10µF ceramic capacitor is usually enough for these conditions. Setting the Output Voltage The LTC3411A develops a 0.8V reference voltage between the feedback pin, VFB, and the signal ground as shown in Figure 4. The output voltage is set by a resistive divider according to the following formula: ⎛ R2⎞ VOUT ≈ 0.
PAGE 14
LTC3411A Applications Information pin. This prevents the output from discharging to below the regulation point when soft-starting. Mode Selection and Frequency Synchronization The SYNC/MODE pin is a multipurpose pin which provides mode selection and frequency synchronization. Connecting this pin to VIN enables Burst Mode operation, which provides the best low current efficiency at the cost of a higher output voltage ripple.
PAGE 15
LTC3411A Applications Information steady-state value. During this recovery time, VOUT can be monitored for overshoot or ringing that would indicate a stability problem. The initial output voltage step may not be within the bandwidth of the feedback loop, so the standard second order overshoot/DC ratio cannot be used to determine phase margin. The gain of the loop increases with R and the bandwidth of the loop increases with decreasing C.
PAGE 16
LTC3411A Applications Information 3) I2R Losses are calculated from the DC resistances of the internal switches, RSW, and external inductor, RL. In continuous mode, the average output current flowing through inductor L is “chopped” between the internal top and bottom switches.
PAGE 17
LTC3411A Applications Information the LTC3411A. These items are also illustrated graphically in the layout diagram of Figure 7. Check the following in your layout: For cost reasons, a ceramic capacitor will be used. COUT selection is then based on load step droop instead of ESR requirements. For a 5% output droop: COUT ≈ 2.5 1.
PAGE 18
LTC3411A Typical Applications General Purpose Buck Regulator Using Ceramic Capacitors VIN 2.5V TO 5.5V C1 10µF PGND PVIN SVIN RS1 1M BM FC PGOOD LTC3411A SYNC/MODE PS RS2 1M ITH R5 100k PGOOD SW 1.8V PGND R3 12.1k R4 549k C3 680pF VOUT 1.2V/1.5V/1.8V AT 1.25A R2 442k VFB SHDN/RT SGND L1 2.2µH 1.5V R1A 357k 1.
PAGE 19
LTC3411A Package Description Please refer to http://www.linear.com/designtools/packaging/ for the most recent package drawings. DD Package 10-Lead Plastic DFN (3mm × 3mm) (Reference LTC DWG # 05-08-1699 Rev C) 0.70 ±0.05 3.55 ±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 = 0.125 TYP 6 0.40 ±0.10 10 1.65 ±0.10 (2 SIDES) PIN 1 NOTCH R = 0.20 OR 0.
PAGE 20
LTC3411A Package Description Please refer to http://www.linear.com/designtools/packaging/ for the most recent package drawings. MS Package 10-Lead Plastic MSOP (Reference LTC DWG # 05-08-1661 Rev F) 0.889 ±0.127 (.035 ±.005) 5.10 (.201) MIN 3.20 – 3.45 (.126 – .136) 3.00 ±0.102 (.118 ±.004) (NOTE 3) 0.50 0.305 ±0.038 (.0197) (.0120 ±.0015) BSC TYP RECOMMENDED SOLDER PAD LAYOUT 0.254 (.010) 10 9 8 7 6 3.00 ±0.102 (.118 ±.004) (NOTE 4) 4.90 ±0.152 (.193 ±.006) DETAIL “A” 0.497 ±0.076 (.0196 ±.
PAGE 21
LTC3411A Revision History (Revision history begins at Rev B) REV DATE DESCRIPTION B 4/10 Remove θJC from Pin Configuration Section 2 Update Minimum for VSYNC/MODE in Electrical Characteristics 3 Update Note 2 3 Update Pin 11 Description in Pin Functions 7 Changed parameters and limits on VSYNC-MODE test 3 C 10/13 PAGE NUMBER 3411afc Information furnished by Linear Technology Corporation is believed to be accurate and reliable. However, no responsibility is assumed for its use.
PAGE 22
LTC3411A Typical Application 1mm Height, 2MHz, Li-Ion to 1.8V Converter VIN 2.5V TO 4.2V C1 10µF PVIN PGOOD SVIN SW LTC3411A SYNC/MODE ITH R3 13.3k SGND PGND C3 470pF R5 100k L1 0.9µH VFB SHDN/RT R4 178k PGOOD C4 22pF C2 10µF ×2 VOUT 1.8V AT 1.25A R2 887k R1 698k C1, C2: TAIYO YUDEN JMK107BJ106MA L1: FDK MIPW3226DORGM 3411A TA04a Efficiency vs Output Current 100 90 EFFICIENCY (%) 80 70 60 50 40 30 20 10 VOUT = 1.8V fO = 2MHz 0 0.1 1 VIN = 2.7V VIN = 3.6V VIN = 4.