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LTC3565

3565fc

For more information www.linear.com/LTC3565

FEATURES

APPLICATIONS

DESCRIPTION

1.25A, 4MHz, Synchronous

Step-Down DC/DC Converter

The LTC

3565 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 0.6V to 5.5V. Internal synchronous power

switches provide high efﬁciency. The LTC3565’s current

mode architecture and external compensation allow the

transient response to be optimized over a wide range of

loads and output capacitors.

The LTC3565 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.

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

trademarks of Linear Technology Corporation. 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.

Step-Down 2.5V/1.25A Regulator

High Efﬁciency: Up to 95%

Range: 2.5V to 5.5V

High Frequency Operation: Up to 4MHz

Selectable Low Ripple (Typical 25mV

p-p

)

Burst Mode

Operation: I

= 40µA

Stable with Ceramic Capacitors

Uses Tiny Capacitors and Inductor

Low R

DS(ON)

Internal Switches: 0.15Ω

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 0.6V 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/MODE

LTC3565

RUN

PGOOD

ITH

GND

2.2µH

OUT

2.5V

1.25A

2.5V TO 5.5V

22pF

931k

294k

680pF

3565 TA01a

22µF

12.1k

22µF

191k

OUTPUT CURRENT (mA)

0.1 1 10

EFFICIENCY (%)

POWER LOSS (W)

100 1

0.1

0.01

0.001

0.0001

1000100 10000

3565 TA01b

= 2.7V

= 3.6V

= 4.2V

Efﬁciency and Power Loss vs Output Current

TYPICAL APPLICATION

Summary of content (22 pages)

PAGE 1
LTC3565 1.25A, 4MHz, Synchronous Step-Down DC/DC Converter FEATURES n n n n n n n n n n n n n n n DESCRIPTION High Efficiency: Up to 95% VIN Range: 2.5V to 5.5V High Frequency Operation: Up to 4MHz Selectable Low Ripple (Typical 25mVp-p) Burst Mode® Operation: IQ = 40µA Stable with Ceramic Capacitors Uses Tiny Capacitors and Inductor Low RDS(ON) Internal Switches: 0.
PAGE 2
LTC3565 ABSOLUTE MAXIMUM RATINGS (Note 1) PVIN, SVIN Voltages ..................................... –0.3V to 6V VFB, ITH Voltages .......................... –0.3V to (VIN + 0.3V) SYNC/MODE, PGOOD Voltage ...... –0.3V to (VIN + 0.3V) SW Voltage (DC) ........................... –0.3V to (VIN + 0.3V) RUN Voltage ................................................ –0.3V to 6V Operating Junction Temperature Range (Notes 2, 5, 8)......................................... –40°C to 125°C Storage Temperature Range...
PAGE 3
LTC3565 ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the full operating junction temperature range, otherwise specifications are at TJ = 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 Oscillator Frequency fSYNC CONDITIONS MIN TYP MAX UNITS 1.3 330 40 0.1 1.5 450 60 1 1.7 4 4 µA µA µA MHz MHz MHz 2.1 2.5 A 0.15 0.15 0.13 0.13 0.01 0.2 0.
PAGE 4
LTC3565 TYPICAL PERFORMANCE CHARACTERISTICS TJ = 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 0 0.1 5.5 5.0 VOUT = 1.
PAGE 5
LTC3565 TYPICAL PERFORMANCE CHARACTERISTICS TJ = 25°C, VIN = 3.6V, fO = 1MHz, unless otherwise noted. Frequency Variation vs Input Voltage RDS(ON) vs Input Voltage 6 0.30 0.20 0.25 0 –2 RDS(ON) (Ω) 2 RDS(ON) (Ω) FREQUENCY VARIATION (%) 4 RDS(ON) vs Temperature 0.25 0.15 0.10 0.15 0.10 –4 0.05 0.05 MAIN SWITCH SYNCHRONOUS SWITCH –6 –8 2.5 3.0 4.5 4.0 3.5 INPUT VOLTAGE (V) 5.0 0.0 2.5 5.5 3.0 4.5 4.0 3.5 INPUT VOLTAGE (V) 5.0 0.0 –50 5.5 PULSE SKIP Burst Mode OPERATION 0.1 0.
PAGE 6
LTC3565 TYPICAL PERFORMANCE CHARACTERISTICS otherwise noted. Forced Continuous Mode TJ = 25°C, VIN = 3.6V, fO = 1MHz, unless Start-Up from Shutdown Start-Up from Shutdown SW 2V/DIV RUN 2V/DIV RUN 2V/DIV VOUT 50mV/DIV AC COUPLED VOUT 1V/DIV VOUT 1V/DIV IL 500mA/DIV IL 1A/DIV IL 200mA/DIV 2µs/DIV 400µs/DIV VIN = 3.6V VOUT = 1.8V ILOAD = 0A Burst Mode OPERATION 3565 G19 VIN = 3.6V VOUT = 1.
PAGE 7
LTC3565 PIN FUNCTIONS RT (Pin 1): Timing Resistor Pin. The oscillator frequency is programmed by connecting a resistor from this pin to ground. GND (Pin 5, Exposed Pad Pin 11): Main Power Ground Pin. Connect to the (–) terminal of COUT, and (–) terminal of CIN. The exposed pad must be soldered to electrical ground on the PCB. RUN (Pin 2): Converter Enable Pin. Forcing this pin above 1.5V enables this part, while forcing it below 0.3V causes the device to shut down.
PAGE 8
LTC3565 BLOCK DIAGRAM SVIN GND ITH PVIN 7 5 10 6 0.6V VOLTAGE REFERENCE PMOS CURRENT COMPARATOR ITH LIMIT + BCLAMP + – – VFB 9 0.642V + – ERROR AMPLIFIER VB – + BURST COMPARATOR SLOPE COMPENSATION OSCILLATOR 4 SW + 0.558V LOGIC – + PGOOD 8 NMOS COMPARATOR – – 2 1 3 RUN RT SYNC/MODE REVERSE COMPARATOR + 5 GND 3565 BD 3565fc 8 For more information www.linear.
PAGE 9
LTC3565 OPERATION The LTC3565 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
LTC3565 APPLICATIONS INFORMATION A general LTC3565 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
LTC3565 APPLICATIONS INFORMATION shows some typical surface mount inductors that work well in LTC3565 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 Coilcraft Sumida DCR HEIGHT 2.15A 44mΩ 2mm 1.2µH 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
LTC3565 APPLICATIONS INFORMATION is adequate for filtering. The output ripple (ΔVOUT) is determined by:  1   ΔVOUT ≈ ΔIL ESR +  C 8f O OUT   In most cases, 0.1µF to 1µF of ceramic capacitors should also be placed close to the LTC3565 in parallel with the main capacitors for high frequency decoupling. where f = 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.
PAGE 13
LTC3565 APPLICATIONS INFORMATION drop of the first cycle. Thus, a good place to start is with the output capacitor value of approximately: COUT ≈ 2.5 ΔIOUT fO • VDROOP More capacitance may be required depending on the duty cycle and load step requirements. 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.
PAGE 14
LTC3565 APPLICATIONS INFORMATION Checking Transient Response The OPTI-LOOP® compensation allows the transient response to be optimized for a wide range of loads and output capacitors. The availability of the ITH pin not only allows optimization of the control loop behavior but also provides a DC coupled and AC filtered closed loop response test point. The DC step, rise time and settling time at this test point truly reflects the closed loop response.
PAGE 15
LTC3565 APPLICATIONS INFORMATION Although a buck regulator is capable of providing the full output current in dropout, it should be noted that as the input voltage VIN drops toward VOUT, the load step capability does decrease due to the decreasing voltage across the inductor. Applications that require large load step capability near dropout should use a different topology such as SEPIC, Zeta or single inductor, positive buck/boost.
PAGE 16
LTC3565 APPLICATIONS INFORMATION losses including diode conduction losses during dead-time and inductor core losses, which generally account for less than 2% total additional loss. Thermal Considerations In a majority of applications, the LTC3565 does not dissipate much heat due to its high efficiency.
PAGE 17
LTC3565 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 0.6V feedback voltage makes R1~300k. A close standard 1% resistor value is 294k then R2 is 931k. The compensation should be optimized for these components by examining the load step response but a good place to start for the LTC3565 is with a 12.1kΩ and 680pF filter.
PAGE 18
LTC3565 TYPICAL APPLICATION General Purpose Buck Regulator Using Ceramic Capacitors VIN 2.5V TO 5.5V C1 22µF PVIN SVIN RS1 1M BM FC PGOOD LTC3565 SYNC/MODE PS RS2 1M ITH R5 100k PGOOD L1 2.2µH SW R2 294k VFB VOUT 1.8V/1.5V/1.2V AT 1.25A SHDN/RT 1.8V GND R3 12.1k R4 191k C3 680pF R1A 147k 1.5V 1.
PAGE 19
LTC3565 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
LTC3565 PACKAGE DESCRIPTION Please refer to http://www.linear.com/designtools/packaging/ for the most recent package drawings. MSE Package 10-Lead Plastic MSOP, Exposed Die Pad (Reference LTC DWG # 05-08-1664 Rev I) BOTTOM VIEW OF EXPOSED PAD OPTION 1.88 ±0.102 (.074 ±.004) 5.10 (.201) MIN 1.68 ±0.102 (.066 ±.004) 0.05 REF 10 0.305 ± 0.038 (.0120 ±.0015) TYP RECOMMENDED SOLDER PAD LAYOUT 3.00 ±0.102 (.118 ±.004) (NOTE 3) DETAIL “B” CORNER TAIL IS PART OF DETAIL “B” THE LEADFRAME FEATURE.
PAGE 21
LTC3565 REVISION HISTORY REV DATE DESCRIPTION PAGE NUMBER A 2/10 Changes to Electrical Characteristics Change TA = 25°C to TJ = 25°C B C 03/12 10/13 2, 3 2, 3, 4, 5, 6 Changes to Pin Functions (GND Pin 5) 8 Changes to Block Diagram 9 Updated Related Parts Table 20 Changed Top Marking for DFN Package 2 Clarified Temperature Grade Test Conditions 3 Added note for website referral for most recent package drawings 20 Changed parameters and limits on VSYNC-MODE test 3 3565fc Informatio
PAGE 22
LTC3565 TYPICAL APPLICATION 1mm Height, 2MHz, Li-Ion to 1.8V Converter Efficiency vs Output Current 100 C1 10µF PVIN PGOOD SVIN SW LTC3565 RUN SYNC/MODE ITH R5 100k GND PGOOD L1 0.9µH VFB R3 13.3k C3 470pF 90 RT R4 80.6k C4, 22pF 80 VOUT 1.8V AT 1.25A EFFICIENCY (%) VIN 2.5V TO 4.2V C2 10µF ×2 R2 R1 464k 232k 70 60 50 40 30 20 10 C1, C2: TAIYO YUDEN JMK107BJ106MA L1: FDK MIPW3226DORGM 0 0.1 3565 TA04a VIN = 2.7V VIN = 3.6V VIN = 4.2V VOUT = 1.