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LTC3440

3440fb

■

Palmtop Computers

■

Handheld Instruments

■

MP3 Players

■

Digital Cameras

Micropower Synchronous

Buck-Boost DC/DC Converter

■

Single Inductor

■

Fixed Frequency Operation with Battery Voltages

Above, Below or Equal to the Output

■

Synchronous Rectification: Up to 96% Efficiency

■

25μA Quiescent Current in Burst Mode

Operation

■

Up to 600mA Continuous Output Current

■

No Schottky Diodes Required (V

OUT

< 4.3V)

■

OUT

Disconnected from V

During Shutdown

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2.5V to 5.5V Input and Output Range

■

Programmable Oscillator Frequency

from 300kHz to 2MHz

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Synchronizable Oscillator

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Burst Mode Enable Control

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<1μA Shutdown Current

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Small Thermally Enhanced 10-Pin MSOP and

(3mm

3mm) DFN Packages

The LTC

3440 is a high efficiency, fixed frequency, Buck-

Boost DC/DC converter that operates from input voltages

above, below or equal to the output voltage. The topology

incorporated in the IC provides a continuous transfer

function through all operating modes, making the product

ideal for single lithium-ion, multicell alkaline or NiMH

applications where the output voltage is within the battery

voltage range.

The device includes two 0.19Ω N-channel MOSFET

switches and two 0.22Ω P-channel switches. Switching

frequencies up to 2MHz are programmed with an external

resistor and the oscillator can be synchronized to an

external clock. Quiescent current is only 25μA in Burst

Mode operation, maximizing battery life in portable appli-

cations. Burst Mode operation is user controlled and can

be enabled by driving the MODE/SYNC pin high. If the

MODE/SYNC pin has either a clock or is driven low, then

fixed frequency switching is enabled.

Other features include a 1μA shutdown, soft-start con-

trol, thermal shutdown and current limit. The LTC3440 is

available in the 10-pin thermally enhanced MSOP and

(3mm × 3mm) DFN packages.

Burst Mode is a registered trademark of Linear Technology Corporation.

Protected by U.S. Patents including 6404251, 6166527.

Efficiency vs V

Li-Ion to 3.3V at 600mA Buck-Boost Converter

FEATURES

DESCRIPTIO

APPLICATIO S

TYPICAL APPLICATIO

SW1

SHDN/SS

MODE/SYNC

SW2

OUT

GND

LTC3440

10μH

340k

200k

15k

3440 TA01

60.4k

C1: TAIYO YUDEN JMK212BJ106MG

C2: TAIYO YUDEN JMK325BJ226MM

L1: SUMIDA CDRH6D38-100

*1 = Burst Mode OPERATION

0 = FIXED FREQUENCY

10μF

Li-Ion

2.7V TO 4.2V

C5 1.5nF

22μF

OUT

3.3V

600mA

(V)

2.5

EFFICIENCY (%)

3.0

3.5

4.0 4.5

3440 TA02

5.0

100

5.5

OUT

= 3.3V

OUT

= 100mA

OSC

= 1MHz

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

Summary of content (20 pages)

PAGE 1
LTC3440 Micropower Synchronous Buck-Boost DC/DC Converter U FEATURES DESCRIPTIO ■ The LTC®3440 is a high efficiency, fixed frequency, BuckBoost DC/DC converter that operates from input voltages above, below or equal to the output voltage. The topology incorporated in the IC provides a continuous transfer function through all operating modes, making the product ideal for single lithium-ion, multicell alkaline or NiMH applications where the output voltage is within the battery voltage range.
PAGE 2
LTC3440 W W W AXI U U ABSOLUTE RATI GS (Note 1) VIN, VOUT Voltage........................................ – 0.3V to 6V SW1, SW2 Voltage ..................................... – 0.3V to 6V VC, RT, FB, SHDN/SS, MODE/SYNC Voltage .................................. – 0.3V to 6V Operating Temperature Range (Note 2) .. – 40°C to 85°C Storage Temperature Range ................. – 65°C to 125°C Lead Temperature (Soldering, 10 sec)..................
PAGE 3
LTC3440 ELECTRICAL CHARACTERISTICS The ● denotes specifications that apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VIN = VOUT = 3.6V, RT = 60k, unless otherwise noted. PARAMETER CONDITIONS MIN TYP Error Amp AVOL MAX UNITS 90 dB Error Amp Source Current 15 μA Error Amp Sink Current 380 μA SHDN/SS Threshold When IC is Enabled When EA is at Maximum Boost Duty Cycle SHDN/SS Input Current VSHDN = 5.
PAGE 4
LTC3440 U W TYPICAL PERFOR A CE CHARACTERISTICS Switch Pins in Buck Mode SW1 2V/DIV Buck VIN = 5V SW1 2V/DIV VOUT 10mV/DIV AC Coupled SW2 2V/DIV Boost VIN = 2.5V 250ns/DIV 3440 G07 VIN = 2.5V VOUT = 3.3V IOUT = 250mA Active Quiescent Current 5 35 65 TEMPERATURE (°C) 95 VIN = VOUT = 3.6V 30 20 10 –55 125 –25 5 35 65 TEMPERATURE (°C) 95 3440 G10 125 3440 G13 5 35 65 TEMPERATURE (°C) 95 VIN = VOUT = 3.6V SWITCHES B AND C 0.20 0.
PAGE 5
LTC3440 U W TYPICAL PERFOR A CE CHARACTERISTICS Feedback Voltage Line Regulation Error Amp Sink Current 430 E/A SINK CURRENT (μA) LINE REGULATION (dB) VIN = VOUT = 2.5V TO 5.5V 80 70 60 –55 –25 5 35 65 TEMPERATURE (°C) 95 0.30 VIN = VOUT = 3.6V 410 390 370 –25 5 35 65 TEMPERATURE (°C) 95 Minimum Start Voltage 80 75 5 35 65 TEMPERATURE (°C) 95 125 3440 G19 5 35 65 TEMPERATURE (°C) 95 125 Current Limit 3000 VIN = VOUT = 3.
PAGE 6
LTC3440 U U U PI FU CTIO S RT (Pin 1): Timing Resistor to Program the Oscillator Frequency. The programming frequency range is 300kHz to 2MHz. fOSC = 6 • 1010 Hz RT MODE/SYNC (Pin 2): MODE/SYNC = External CLK : Synchronization of the internal oscillator. A clock frequency of twice the desired switching frequency and with a pulse width between 100ns and 2μs is applied. The oscillator free running frequency is set slower than the desired synchronized switching frequency to guarantee sync.
PAGE 7
LTC3440 W BLOCK DIAGRA SW1 3 4 SW2 SW A SW D 7 6 SW B GATE DRIVERS AND ANTICROSS CONDUCTION –0.4A SW C – + VOUT 2.5V TO 5.5V VOUT + VIN 2.5V TO 5.5V ISENSE AMP REVERSE CURRENT LIMIT SUPPLY CURRENT LIMIT – + UVLO + RT RT + 1.22V R1 – PWM COMPARATORS 9 CLAMP – 10 1 FB + 2.4V PWM LOGIC AND OUTPUT PHASING – – + 2.
PAGE 8
LTC3440 U OPERATIO The LTC3440 provides high efficiency, low noise power for applications such as portable instrumentation. The LTC proprietary topology allows input voltages above, below or equal to the output voltage by properly phasing the output switches. The error amp output voltage on the VC pin determines the output duty cycle of the switches. Since the VC pin is a filtered signal, it provides rejection of frequencies from well below the switching frequency.
PAGE 9
LTC3440 U OPERATIO 75% DMAX BOOST V4 (≈2.05V) A ON, B OFF BOOST REGION PWM CD SWITCHES DMIN BOOST DMAX BUCK V3 (≈1.65V) FOUR SWITCH PWM BUCK/BOOST REGION The input voltage, VIN, where the four switch region begins is given by: VIN = VOUT V 1 – (150ns • f) V2 (≈1.55V) The point at which the four switch region ends is given by: D ON, C OFF PWM AB SWITCHES BUCK REGION V1 (≈0.9V) 0% DUTY CYCLE 3440 F02 INTERNAL CONTROL VOLTAGE, VCI Figure 2.
PAGE 10
LTC3440 U OPERATIO voltage from the error amp to determine the control mode, therefore full-time 4-switch mode is required to maintain the Buck/Boost function. The efficiency below 1mA becomes dominated primarily by the quiescent current and not the peak efficiency.
PAGE 11
LTC3440 U OPERATIO SOFT-START The soft-start function is combined with shutdown. When the SHDN/SS pin is brought above typically 1V, the IC is enabled but the EA duty cycle is clamped from the VC pin. A detailed diagram of this function is shown in Figure 5. The components RSS and CSS provide a slow ramping voltage on the SHDN/SS pin to provide a soft-start function. ERROR AMP VIN 15μA + VOUT 1.
PAGE 12
LTC3440 U W U U APPLICATIO S I FOR ATIO Ripple = allowable inductor current ripple (e.g., 0.2 = 20%) VIN(MIN) = minimum input voltage, V VIN(MAX) = maximum input voltage, V VOUT = output voltage, V IOUT(MAX) = maximum output load current The output capacitance is usually many times larger in order to handle the transient response of the converter.
PAGE 13
LTC3440 U W U U APPLICATIO S I FOR ATIO Output Voltage > 4.3V Closing the Feedback Loop A Schottky diode from SW to VOUT is required for output voltages over 4.3V. The diode must be located as close to the pins as possible in order to reduce the peak voltage on SW2 due to the parasitic lead and trace inductance. The LTC3440 incorporates voltage mode PWM control. The control to output gain varies with operation region (Buck, Boost, Buck-Boost), but is usually no greater than 15.
PAGE 14
LTC3440 U W U U APPLICATIO S I FOR ATIO 1 Hz 2 • π • 32 e3 • R1 • CP1 Which is extremely close to DC 1 fZERO1 = Hz 2 • π • RZ • CP1 1 fZERO2 = Hz 2 • π •R1 • CZ 1 fPOLE1 ≈ 1 Hz 2 • π • RZ • CP 2 fPOLE2 = VOUT + 1.22V ERROR AMP R1 FB – 9 CP1 VC 10 R2 3440 F07 Figure 7. Error Amplifier with Type I Compensation Restart Circuit VOUT + ERROR AMP – 1.22V R1 CZ1 FB 9 VC CP1 RZ traces and external components. Following the recommendations for output voltage >4.3V and input voltage >4.
PAGE 15
LTC3440 U W U U APPLICATIO S I FOR ATIO Simple Average Input Current Control INPUT_VOLTAGE A simple average current limit circuit is shown in Figure 10. Once the input current of the IC is above approximately 1A, Q1 will start sourcing current into the FB pin and lower the output voltage to maintain the average input current. Since the voltage loop is utilized to perform average current limit, the voltage control loop is maintained and the VC voltage does not slam.
PAGE 16
LTC3440 U TYPICAL APPLICATIO S 3-Cell to 5V Boost Converter with Output Disconnect L1 10μH 3-Cell to 5V Boost Efficiency D1** VOUT 5V 300mA 4 SW1 SW2 LTC3440 6 7 VIN VOUT 3 R4 1M 8 + 3 CELLS 2 C1 10μF SD C3 * 0.1μF 1 SHDN/SS FB MODE/SYNC VC RT GND 90 80 R1 619k 9 C2** 22μF 15k 10 5 C4 1.5nF R2 200k RT = 1MHz f 60.4k OSC VIN = 4.5V Burst Mode OPERATION 70 EFFICIENCY (%) VIN = 2.7V TO 4.5V 100 VIN = 3.6V VIN = 2.
PAGE 17
LTC3440 U TYPICAL APPLICATIO S Efficiency of the WCDMA Power Amp Power Supply WCDMA Power Amp Power Supply with Dynamic Voltage Control VOUT = 3.3V – 1.7V • (VDAC – 1.22V) Li-Ion + C1 * 10μF 2 1 FB MODE/SYNC RT VC GND R1 340k 10 R3 15k C4 150pF IOUT = 100mA 94 92 IOUT = 250mA 90 88 IOUT = 600mA 86 84 5 C2** 10μF R2 200k C5 10pF RT 30.1k fOSC = 2MHz *1 = Burst Mode OPERATION 0 = FIXED FREQUENCY ** LOCATE COMPONENTS AS CLOSE TO IC AS POSSIBLE R5 10k R6 200k 9 VOUT = 3.
PAGE 18
LTC3440 U PACKAGE DESCRIPTIO DD Package 10-Lead Plastic DFN (3mm × 3mm) (Reference LTC DWG # 05-08-1699) R = 0.115 TYP 6 0.38 ± 0.10 10 0.675 ±0.05 3.50 ±0.05 1.65 ±0.05 2.15 ±0.05 (2 SIDES) 3.00 ±0.10 (4 SIDES) PACKAGE OUTLINE 1.65 ± 0.10 (2 SIDES) PIN 1 TOP MARK (SEE NOTE 6) (DD10) DFN 1103 5 0.25 ± 0.05 0.200 REF 0.50 BSC 2.38 ±0.05 (2 SIDES) RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS 1 0.75 ±0.05 0.00 – 0.05 0.25 ± 0.05 0.50 BSC 2.38 ±0.10 (2 SIDES) BOTTOM VIEW—EXPOSED PAD NOTE: 1.
PAGE 19
LTC3440 U PACKAGE DESCRIPTIO MS Package 10-Lead Plastic MSOP (Reference LTC DWG # 05-08-1661) 0.889 ± 0.127 (.035 ± .005) 5.23 (.206) 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 ± .003) REF 0° – 6° TYP GAUGE PLANE 1 2 3 4 5 0.53 ± 0.152 (.021 ± .006) DETAIL “A” 0.86 (.
PAGE 20
LTC3440 U TYPICAL APPLICATIO Li-Ion to 3.3V at 600mA Buck-Boost Converter Efficiency L1 10μH 220pF 8 Li-Ion 2 + C1 * 10μF 1 SHDN/SS FB MODE/SYNC VC RT GND R1 340k RT 60.4k *1 = Burst Mode OPERATION 0 = FIXED FREQUENCY 2.2k C2 22μF C5 300pF 10 R3 15k 90 80 9 5 100 EFFICIENCY (%) 4 SW1 SW2 LTC3440 6 7 VIN VOUT 3 VIN = 2.8V TO 4.2V VOUT 3.3V 600mA Burst Mode OPERATION 70 60 50 VIN = 4.2V VIN = 3.