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LTC3458

3458fa

FEATURES

DESCRIPTIO

APPLICATIO S

TYPICAL APPLICATIO

■

High Efficiency: Up to 93%

■

Inrush Current Limiting and Output Disconnect

■

Programmable Output Voltages up to 7.5V

■

1.5V to 6V Input Range

■

Programmable/Synchronizable Fixed Frequency

Operation up to 1.5MHz

■

Programmable Automatic Burst Mode

Operation

■

Current Mode Control with Programmable Soft-Start

Period and Peak Current Limit

■

700mA at 7V from 5V Input

■

0.3Ω N-Channel and 0.4Ω P-Channel 1.4A Switches

at 5V

OUT

■

Ultralow Quiescent Currents: 15μA Sleep, <1μA in

Shutdown

■

3mm × 4mm Thermally Enhanced DFN Package

■

Point-of-Load Regulators

■

USB V

BUS

Power

■

LCD Bias

■

OLED Displays

1.4A, 1.5MHz Synchronous

Step-Up DC/DC Converter

with Output Disconnect

The LTC

3458 is a high efficiency, current mode, fixed

frequency, step up DC/DC converter with true output

disconnect and inrush current limiting. The LTC3458 is

rated for a 7.5V output and includes a 0.3Ω N-channel

MOSFET switch and a 0.4Ω P-channel MOSFET synchro-

nous rectifier. The LTC3458 is well suited for battery

powered applications and includes programmable output

voltage, switching frequency and loop compensation. The

oscillator frequency can be set up to 1.5MHz or synchro-

nized to an external clock.

Quiescent current is only 15μA during Burst Mode opera-

tion maximizing battery life in portable applications. The

Burst Mode current threshold, peak current limit, and soft-

start are externally programmable. Other features include

<1μA shutdown current, antiringing control, and thermal

limit. The LTC3458 is available in a low profile (0.75mm),

3mm × 4mm 12-pin DFN package.

USB to 7V at 1MHz

Burst Mode is a registered trademark of Linear Technology Corporation.

USB to 7V

OUT

GND/PGND

SHDN

SYNC

LIM

OUT

COMP

BURST

LTC3458

USB

4.35V to 5.25V

2.2μF

COEV

10μH

DQ7545

ON OFF

200k 124k 133k

316k

33k

0.01μF

560pF

10pF

1.5M

22μF

X5R

OUT

500mA

3458 TA01a

LOAD CURRENT (mA)

EFFICIENCY

POWER LOSS (mW)

100

1000

0.1

0.1 10 100 1000

3458 TA01b

5.25V

4.35V

POWER LOSS

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

All other trademarks are the property of their respective owners.

Summary of content (16 pages)

PAGE 1
LTC3458 1.4A, 1.5MHz Synchronous Step-Up DC/DC Converter with Output Disconnect DESCRIPTIO U FEATURES ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ High Efficiency: Up to 93% Inrush Current Limiting and Output Disconnect Programmable Output Voltages up to 7.5V 1.5V to 6V Input Range Programmable/Synchronizable Fixed Frequency Operation up to 1.5MHz Programmable Automatic Burst Mode® Operation Current Mode Control with Programmable Soft-Start Period and Peak Current Limit 700mA at 7V from 5V Input 0.3Ω N-Channel and 0.
PAGE 2
LTC3458 W W U W ABSOLUTE AXI U RATI GS PIN CONFIGURATION (Note 1) VIN, SS, SYNC Voltages ................................. –0.3 to 7V BURST, SHDN, VOUT Voltages ....................... –0.3 to 8V Operating Temperature Range (Notes 2, 3) .........................................–40°C to 85°C Storage Temperature Range ..................–65°C to 125°C SW Voltage DC ........................................................... –0.3V to 8V Pulsed <100ns ...................................... –0.
PAGE 3
LTC3458 ELECTRICAL CHARACTERISTICS The ● denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VIN = 3.3V, VOUT = 5V, RT = 200k, unless otherwise noted. PARAMETER CONDITIONS MIN Error Amplifier Sink Current ● SYNC Input Low ● SHDN Input High ● SHDN Input Low ● BURST Mode Peak Current U W ILIMIT, IBURST, TZERO Currents 0.35 0.3 CURRENT (μA) CURRENT (A) CURRENT (mA) IBURST PEAK 400 1.6 –200 2.0 10 IVOUT 2.5 3.
PAGE 4
LTC3458 U W TYPICAL PERFOR A CE CHARACTERISTICS Frequency Accuracy Efficiency vs Frequency 1.01 0.99 0.4 91 89 87 0.97 0.95 –45 –30 –15 0 15 30 45 60 TEMPERATURE (°C) 75 85 500 90 0.3 N-CHANNEL 0.2 700 1100 1300 900 FREQUENCY (kHz) 0 –40 1500 –15 35 10 TEMPERATURE (°C) 60 3458 G08 1200 85 3458 G09 SHDN Pin Threshold and Hysteresis Maximum Load Current 1.8 to 5.5VIN at 700kHz RILIM = 124k P-CHANNEL 0.1 3458 G07 SYNC Pin Threshold 1.5 1.0 5VOUT 1.4 0.9 1.3 3.3VOUT 600 7.
PAGE 5
LTC3458 U W TYPICAL PERFOR A CE CHARACTERISTICS Fixed Frequency (FF) Discontinuous Current Fixed Frequency (FF) Continuous Current IL 200mA/DIV SW 2V/DIV SW 2V/DIV IL 100mA/DIV 0mA 0mA VIN = 3.3V VOUT = 7V L = 10μH VIN = 3.3V VOUT = 7V L = 10μH 200ns/DIV Over-Current with 1.5A ILIMIT 200ns/DIV Burst Mode Operation VOUT 100mV/DIV SW 2V/DIV SW 5V/DIV IL 0.5A/DIV IL 200mA/DIV 0mA VIN = 3.3V VOUT = 7V L = 10μH RILIM = 133k VIN = 3.
PAGE 6
LTC3458 U W TYPICAL PERFOR A CE CHARACTERISTICS Sync Operation at 1.33MHz FF Mode 100-300mA Load Step SW 5V/DIV VOUT 200mV/DIV SYNC 2V/DIV COMP 500mV/DIV IL 200mA/DIV IL 0.5A/DIV 0mA 0mA VIN = 3.3V VOUT = 7V ROSC = 200k 500ns/DIV VIN = 3.
PAGE 7
LTC3458 U U U PI FU CTIO S SW (Pin 1): Switch Pin for Inductor Connection. During discontinuous conduction mode an antiring resistor connects SW to VIN to reduce noise. VIN (Pin 2): Input Supply Pin. Connect this to the input supply and decouple with 1μF minimum. SYNC (Pin 3): Oscillator Synchronization Pin. A clock pulse width of 100ns to 2μs is required to synchronize the internal oscillator. This pin is disabled when grounded. SHDN (Pin 4): Shutdown Pin. Grounding this pin shuts down the IC.
PAGE 8
LTC3458 W BLOCK DIAGRA BURST SW VCC 11 1 2 VCC 3 OSC/SYNC RT 6 MAX DUTY CLOCK SYNC ANTIRING SLOPE UNDER BURST MODE CONTROL P-DRIVE N-DRIVE + MODE VBEST IZERO SW1 IZERO DETECT P-DRIVE PWM AND BURST MODE 12 VOUT N-DRIVE P-DRIVE DRIVE LOGIC 4% UNDERVOLTAGE UNDER SLEEP IPEAK – VSELECT MODE FIXED FREQUENCY BURST MODE MUX SLEEP CONTROL ICOMP/LIMIT_PEAK IBURST_PEAK SLOPE PGND SLEEP TO ALL BLOCKS BURST ACTIVE – 7 FB VCC + (DISABLED IN BURST MODE) PEAK CURRENT COMPARATOR
PAGE 9
LTC3458 U W U U APPLICATIO S I FOR ATIO Error Amp. The error amplifier is a transconductance type, with its positive input internally connected to the 1.23V reference, and its negative input connected to FB. A simple compensation network is placed from COMP to ground. Internal clamps limit the minimum and maximum error amp output voltage for improved large signal transient response.
PAGE 10
LTC3458 U W U U APPLICATIO S I FOR ATIO transition occurs using a single resistor. During Burst Mode operation, the oscillator is shut down, since the on time is determined by the time it takes the inductor current to reach a fixed peak current, and the off time is determined by the time it takes for the inductor current to return to zero.
PAGE 11
LTC3458 U W U U APPLICATIO S I FOR ATIO COMPONENT SELECTION Some example inductor part types are: Inductor Selection The high frequency operation of the LTC3458 allows for the use of small surface mount inductors. Since the internal slope compensation circuit relies on the inductor’s current slope and frequency, Table 1 should be used to select an inductor value for a given frequency of operation (± 25%).
PAGE 12
LTC3458 U W U U APPLICATIO S I FOR ATIO Input Capacitor Selection Compensating the Feedback Loop The input filter capacitor reduces peak currents drawn from the input source and reduces input switching noise. In most applications >1μF per amp of peak input current is recommended. See Table 3 for a list of capacitor manufacturers for input and output capacitor selection. The LTC3458 uses current mode control, with internal adaptive slope compensation.
PAGE 13
LTC3458 U W U U APPLICATIO S I FOR ATIO The typical error amp compensation is shown in Figure 2. The equations for the loop dynamics are as follows: fPOLE1 ≈ 1 2π • 10e 6 • CC1 1 fZERO1 = 2π • RZ • CC1 1 fPOLE2 ≈ 2π • RZ • CC 2 VOUT 1.25V rolled off before the RHP zero frequency.
PAGE 14
LTC3458 U TYPICAL APPLICATIO S Lithium-Ion to 5V, 500mA at 850kHz WURTH 12μH 774775112 Li-Ion to 5VOUT 100 LTC3458 10pF FB SHDN ON OFF 1M 33k SS RT 0.01μF 124k 80 70 22μF X5R 10pF 65 0.1 BURST ILIM 2.5VIN 85 75 324k 0.01μF 3.6VIN 90 COMP SYNC 243k VOUT 5V 450mA VOUT GND/PGND 4.2VIN 95 SW VIN 2.2μF EFFICIENCY Li-Ion 2.5V to 4.
PAGE 15
LTC3458 U PACKAGE DESCRIPTIO DE/UE Package 12-Lead Plastic DFN (4mm × 3mm) (Reference LTC DWG # 05-08-1695) 0.70 ±0.05 3.60 ±0.05 2.20 ±0.05 3.30 ±0.05 1.70 ± 0.05 PACKAGE OUTLINE 0.25 ± 0.05 0.50 BSC 2.50 REF RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS APPLY SOLDER MASK TO AREAS THAT ARE NOT SOLDERED 4.00 ±0.10 (2 SIDES) 7 R = 0.115 TYP 0.40 ± 0.10 12 R = 0.05 TYP PIN 1 TOP MARK (NOTE 6) 0.200 REF 3.00 ±0.10 (2 SIDES) 0.75 ±0.05 3.30 ±0.10 1.70 ± 0.10 6 0.25 ± 0.05 PIN 1 NOTCH R = 0.
PAGE 16
LTC3458 U TYPICAL APPLICATIO Dual Lumiled Application with BURST Pin Current Regulation L1 2-Lumileds in Series SW VIN Li-Ion 2.7V to 4.2V CIN 2.2μF fOSC = 850kHz LTC3458 GND/PGND 100 VOUT 6.4V TO 6.8V VOUT 90 Z1 SHDN SYNC COMP D1 0.01μF RT 33k SS COUT 2.2μF 0.01μF ILIM 243k 150mA, 6.4V FB EFFICIENCY (%) ON OFF 124k RBURST 350mA, 6.8V 70 60 D2 BURST 250mA, 6.6V 80 NOTE: LUMILED CURRENT REGULATION ~10% OVER VIN RANGE 0.01μF 50 2.