Datasheet

ManualsBrandsLINEAR TECHNOLOGY ManualsPMICsPMIC - DC/DC voltage regulator Converter, Converter/amplifier DFN 10

LTC3411

3411fb

TYPICAL APPLICATION

FEATURES

APPLICATIONS

DESCRIPTION

1.25A, 4MHz, Synchronous

Step-Down DC/DC Converter

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

Burst Mode is a registered trademark of Linear Technology Corporation.

Figure 1. Step-Down 2.5V/1.25A Regulator

Efﬁ ciency vs Load Current

Small 10-Lead MSOP or DFN Package

Uses Tiny Capacitors and Inductor

High Frequency Operation: Up to 4MHz

High Switch Current: 1.6A

Low R

DS(ON)

Internal Switches: 0.110Ω

High Efﬁ ciency: Up to 95%

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

Low Quiescent Current: 60μA

Output Voltages from 0.8V to 5V

Selectable Burst Mode

Operation

Synchronizable to External Clock

Notebook Computers

Digital Cameras

Cellular Phones

Handheld Instruments

Board Mounted Power Supplies

The LTC

3411 is a constant frequency, synchronous,

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

applications, it operates from a 2.63V to 5.5V input voltage

range and has a user conﬁ gurable operating frequency

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

and inductors 2mm or less in height. The output voltage

is adjustable from 0.8V to 5V. Internal sychronous 0.11Ω

power switches with 1.6A peak current ratings provide

high efﬁ ciency. The LTC3411’s current mode architecture

and external compensation allow the transient response

to be optimized over a wide range of loads and output

capacitors.

The LTC3411 can be conﬁ gured for automatic power sav-

ing Burst Mode operation to reduce gate charge losses

when the load current drops below the level required for

continuous operation. For reduced noise and RF interfer-

ence, the SYNC/MODE pin can be conﬁ gured 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)

with a low quiescent current of 60μA. In shutdown, the

device draws <1μA.

SYNC/MODEV

LTC3411

PGOOD

SHDN/R

PGNDSGND

2.2μH

OUT

2.5V/1.25A

2.63V TO 5.5V

887k

412k

1000pF

3411 F01

22μF

13k

22μF

324k

NOTE: IN DROPOUT, THE OUTPUT TRACKS

THE INPUT VOLTAGE

C1, C2: TAIYO YUDEN JMK325BJ226MM

L1: TOKO A914BYW-2R2M (D52LC SERIES)

LOAD CURRENT (mA)

EFFICIENCY (%)

100

1 100 1000

3411 TA01

= 3.3V

OUT

= 2.5V

= 1MHz

Burst Mode OPERATION

Summary of content (24 pages)

PAGE 1
LTC3411 1.25A, 4MHz, Synchronous Step-Down DC/DC Converter FEATURES DESCRIPTION n The LTC®3411 is a constant frequency, synchronous, step- down DC/DC converter. Intended for medium power applications, it operates from a 2.63V 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 2mm or less in height. The output voltage is adjustable from 0.8V to 5V. Internal sychronous 0.11Ω power switches with 1.
PAGE 2
LTC3411 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 Temperature Range (Note 2) LTC3411E............................................. –40°C to 85°C LTC3411I............................
PAGE 3
LTC3411 ELECTRICAL CHARACTERISTICS The l denotes the speciﬁcations which apply over the full operating temperature range, otherwise speciﬁcations are at TA = 25°C. VIN = 3.3V, RT = 324k unless otherwise speciﬁed. (Note 2) SYMBOL PARAMETER VIN Operating Voltage Range CONDITIONS MIN TYP 2.625 IFB Feedback Pin Input Current VFB Feedback Voltage (Note 3) ΔVLINEREG Reference Voltage Line Regulation VIN = 2.7V to 5V l 0.784 l l MAX UNITS 5.5 V ±0.1 μA 0.8 0.816 V 0.04 0.2 %/V 0.
PAGE 4
LTC3411 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. SYNC/MODE (Pin 2): Combination Mode Selection and Oscillator Synchronization Pin. This pin controls the operation of the device. When tied to SVIN or SGND, Burst Mode operation or pulse skipping mode is selected, respectively.
PAGE 5
LTC3411 PIN FUNCTIONS NOMINAL (V) PIN NAME 1 SHDN/RT 2 SYNC/MODE 3 SGND ABSOLUTE MAX (V) DESCRIPTION MIN TYP MAX MIN MAX Shutdown/Timing Resistor –0.3 0.8 SVIN –0.3 SVIN + 0.3 SVIN –0.3 SVIN + 0.3 PVIN –0.3 PVIN + 0.3 Mode Select/Sychronization Pin 0 Signal Ground 0 4 SW 5 PGND Switch Node Main Power Ground 0 0 6 PVIN Main Power Supply –0.3 5.5 –0.3 SVIN + 0.3 7 SVIN Signal Power Supply 2.5 5.5 –0.3 6 8 PGOOD Power Good Pin 0 SVIN –0.
PAGE 6
LTC3411 TYPICAL PERFORMANCE CHARACTERISTICS Load Regulation 0.3 Burst Mode OPERATION VIN = 3.3V VOUT = 2.5V 0 FORCED CONTINUOUS –0.1 VOUT = 1.8V TA = 25°C –0.2 0.35 0.30 0.25 0.20 IOUT = 1.25A 0.15 –0.3 0.10 –0.4 0.05 IOUT = 400mA 1 10 100 1000 LOAD CURRENT (mA) 10000 4 2 0 –2 –4 –6 –10 2 3 4 VIN (V) 5 3411 G07 2 6 100 6 –4 6 RDS(ON) vs VIN TA = 25°C 115 95 RDS(ON) (mΩ) EFFICIENCY (%) 4 0 5 120 VIN = 3.3V VOUT = 2.
PAGE 7
LTC3411 BLOCK DIAGRAM SVIN SGND ITH PVIN 7 3 10 6 0.8V PMOS CURRENT COMPARATOR ITH LIMIT VOLTAGE REFERENCE + BCLAMP + – – VFB 9 ERROR AMPLIFIER VB 0.74V + – B – + BURST COMPARATOR HYSTERESIS = 80mV SLOPE COMPENSATION OSCILLATOR 4 SW + 0.
PAGE 8
LTC3411 OPERATION The LTC3411 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 amplﬁer compares the divided output voltage with a reference voltage of 0.
PAGE 9
LTC3411 APPLICATIONS INFORMATION A general LTC3411 application circuit is shown in Figure 5. 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 tradeoff between efﬁciency and component size. High frequency operation allows the use of smaller inductor and capacitor values.
PAGE 10
LTC3411 APPLICATIONS INFORMATION higher ripple current which causes this to occur at lower load currents. This causes a dip in efﬁciency in the upper range of low current operation. In Burst Mode operation, lower inductance values will cause the burst frequency to increase. Inductor Core Selection Different core materials and shapes will change the size/current and price/current relationship of an inductor.
PAGE 11
LTC3411 APPLICATIONS INFORMATION where the maximum average output current IMAX equals the peak current minus half the peak-to-peak ripple current, IMAX = ILIM – ΔIL/2. Once the ESR requirements for COUT have been met, the RMS current rating generally far exceeds the IRIPPLE(P-P) requirement, except for an all ceramic solution. This formula has a maximum at VIN = 2VOUT, where IRMS = IOUT/2. This simple worst case is commonly used to design because even signiﬁcant deviations do not offer much relief.
PAGE 12
LTC3411 APPLICATIONS INFORMATION Ceramic Input and Output Capacitors Higher value, lower cost ceramic capacitors are now becoming available in smaller case sizes. These are tempting for switching regulator use because of their very low ESR. Unfortunately, the ESR is so low that it can cause loop stability problems. Solid tantalum capacitor ESR generates a loop “zero” at 5kHz to 50kHz that is instrumental in giving acceptable loop phase margin.
PAGE 13
LTC3411 APPLICATIONS INFORMATION Shutdown and Soft-Start The SHDN/RT pin is a dual purpose pin that sets the oscillator frequency and provides a means to shut down the LTC3411. This pin can be interfaced with control logic in several ways, as shown in Figure 3(a) and Figure 3(b). The ITH pin is primarily for loop compensation, but it can also be used to increase the soft-start time. Soft start reduces surge currents from VIN by gradually increasing the peak inductor current.
PAGE 14
LTC3411 APPLICATIONS INFORMATION overshoot seen at this pin. The bandwidth can also be estimated by examining the rise time at the pin. The ITH external components shown in the Figure 1 circuit will provide an adequate starting point for most applications. The series R-C ﬁlter sets the dominant pole-zero loop compensation. The values can be modiﬁed slightly (from 0.
PAGE 15
LTC3411 APPLICATIONS INFORMATION In some applications, a more severe transient can be caused by switching in loads with large (>1uF) input capacitors. The discharged input 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 switch connecting the load has low resistance and is driven quickly. The solution is to limit the turn-on speed of the load switch driver.
PAGE 16
LTC3411 APPLICATIONS INFORMATION To avoid the LTC3411 from exceeding the maximum junction temperature, the user will need to do some thermal analysis. The goal of the thermal analysis is to determine whether the power dissipated exceeds the maximum junction temperature of the part. The temperature rise is given by: TRISE = PD • θJA where PD is the power dissipated by the regulator and θJA is the thermal resistance from the junction of the die to the ambient temperature.
PAGE 17
LTC3411 APPLICATIONS INFORMATION The output voltage can now be programmed by choosing the values of R1 and R2. To maintain high efﬁciency, the current in these resistors should be kept small. Choosing 2μA with the 0.8V feedback voltage makes R1~400k. A close standard 1% resistor is 412k and R2 is then 887k. The compensation should be optimized for these components by examining the load step response but a good place to start for the LTC3411 is with a 13kΩ and 1000pF ﬁlter.
PAGE 18
LTC3411 TYPICAL APPLICATIONS VIN 2.63V TO 5.5V C1 22μF PGND PVIN SVIN RS1 1M BM PGOOD ITH VOUT 1.8V/2.5V/3.3V AT 1.25A R2 887K SYNC/MODE PS RS2 1M L1 2.2μH SW LTC3411 FC R5 100k PGOOD VFB SHDN/RT 3.3V SGND 2.5V 1.8V PGND C2 22μF C4 22pF R3 13k R4 324k C3 1000pF R1A 280k R1B 412k R1C 698k 3411 F07a SGND SGND GND SGND PGND NOTE: IN DROPOUT, THE OUTPUT TRACKS THE INPUT VOLTAGE C1, C2: TAIYO YUDEN JMK325BJ226MM L1: TOKO A914BYW-2R2M (D52LC SERIES) Figure 7.
PAGE 19
LTC3411 TYPICAL APPLICATIONS Single Inductor, Positive, Buck-Boost Converter C1 22μF VIN 2.63V TO 5V 100k C7 10pF SVIN SW L1 3.3μH D1 SGND VFB SYNC/MODE ITH SHDN/RT R3 13k C2 22μF s2 M1 VIN PGOOD + C4 47μF VOUT 3.
PAGE 20
LTC3411 TYPICAL APPLICATIONS All Ceramic 2-Cell to 3.3V and 1.8V Converters VIN = 2V TO 3V L1 4.7μH D1 VOUT 3.3V 120mA/1A C5 22μF LTC3402 VIN +2 CELLS SHDN 1M VOUT SYNC/MODE PGOOD 604k VC C2 44mF (2 s 22mF) 1000pF RT 49.9k 0 = FIXED FREQ 1 = Burst Mode OPERATION GND PVIN SVIN MODE/SYNC FB PGOOD C1 10μF SW 10pF 1000pF C1: TAIYO YUDEN JMK212BJ106MG C2: TAIYO YUDEN JMK325BJ226MM C5, C6: TAIYO YUDEN JMK325BJ226MM 887k SHDN/RT SGND VOUT 1.8V/1.2A SW ITH 13k 47k LTC3411 L2 2.
PAGE 21
LTC3411 TYPICAL APPLICATION 2mm Height, 2MHz, Li-Ion to 1.8V Converter C6 1μF + R5 100k C1 33μF PVIN PGOOD SVIN SW LTC3411 PGOOD L1 1μH C4 22pF SYNC/MODE ITH C7 47pF R3 15k C3 470pF + C2 33μF C5 1μF VOUT 1.8V AT 1.25A VFB SGND PGND SHDN/RT R4 154k R1 698k R2 887k 3411 TA04 C1, C2: AVX TPSB336K006R0600 C4, C5: TAIYO YUDEN LMK212BJ105MG L1: COILCRAFT DO1606T-102 Efﬁciency vs Load Current 100 95 2.5V 90 EFFICIENCY (%) VIN 2.63V TO 4.2V 85 3.6V 80 75 70 4.2V 65 60 VOUT = 1.
PAGE 22
LTC3411 PACKAGE DESCRIPTION DD Package 10-Lead Plastic DFN (3mm × 3mm) (Reference LTC DWG # 05-08-1699) R = 0.115 TYP 6 0.38 p 0.10 10 0.675 p 0.05 3.50 p 0.05 1.65 p 0.05 2.15 p 0.05 (2 SIDES) 3.00 p 0.10 (4 SIDES) PACKAGE OUTLINE 1.65 p 0.10 (2 SIDES) PIN 1 TOP MARK (SEE NOTE 6) (DD) DFN 1103 5 0.200 REF 0.25 p 0.05 0.50 BSC 2.38 p 0.05 (2 SIDES) 1 0.25 p 0.05 0.50 BSC 0.75 p 0.05 0.00 – 0.05 2.38 p 0.10 (2 SIDES) BOTTOM VIEW—EXPOSED PAD RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS NOTE: 1.
PAGE 23
LTC3411 PACKAGE DESCRIPTION MS Package 10-Lead Plastic MSOP (Reference LTC DWG # 05-08-1661) 0.889 p 0.127 (.035 p .005) 5.23 (.206) MIN 3.20 – 3.45 (.126 – .136) 3.00 p 0.102 (.118 p .004) (NOTE 3) 0.50 0.305 p 0.038 (.0197) (.0120 p .0015) BSC TYP RECOMMENDED SOLDER PAD LAYOUT 0.254 (.010) 10 9 8 7 6 3.00 p 0.102 (.118 p .004) (NOTE 4) 4.90 p 0.152 (.193 p .006) DETAIL “A” 0.497 p 0.076 (.0196 p .003) REF 0° – 6° TYP GAUGE PLANE 1 2 3 4 5 0.53 p 0.152 (.021 p .006) DETAIL “A” 1.10 (.
PAGE 24
LTC3411 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 LT1776 500mA (IOUT) 200kHz High Efﬁciency Step-Down DC/DC Converter 90% Efﬁciency, VIN: 7.4V to 40V, VOUT(MIN): 1.24V, IQ: 3.2mA, ISD: 30μA, N8, S8 LTC1879 1.2A (IOUT) 550kHz Synchronous Step-Down DC/DC Converter 95% Efﬁciency, VIN: 2.7V to 10V, VOUT(MIN): 0.