Datasheet

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LTC3499/LTC3499B

3499fc

TYPICAL APPLICATION

DESCRIPTION

750mA Synchronous

Step-Up DC/DC Converters

with Reverse-Battery Protection

The LTC

3499/LTC3499B are synchronous, fixed frequency

step-up DC/DC power converters with integrated reverse

battery protection that protect and disconnect the devices

and load when the battery polarity is reversed while

delivering high efficiency in a small (3mm × 3mm) DFN

package. True output disconnect eliminates inrush current

and allows zero load current in shutdown.

The devices feature an input voltage range of 1.8V to 5.5V

enabling operation from two alkaline or NiMH batteries. The

switching frequency is internally set at 1.2MHz allowing

the use of tiny surface mount inductors and capacitors.

A minimal number of external components are required

to generate output voltages ranging from 2V to 6V. The

LTC3499 features automatic Burst Mode operation to

increase efficiency at light loads, while the LTC3499B

features continuous switching at light loads.

The soft-start time is externally programmable through a

small capacitor. Anti-ring circuitry reduces EMI emissions

by damping the inductor in discontinuous mode. The de-

vices feature <1µA shutdown supply current, integrated

overvoltage protection and are available in both 8-pin

(3mm × 3mm) DFN and 8-pin MSOP packages.

Two AA Cells to 5V Synchronous Boost Converter

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

Burst Mode is a registered trademark of Linear Technology Corporation.

All other trademarks are the property of their respective owners.

FEATURES

APPLICATIONS

Medical Equipment

Digital Cameras

MP3 Players

Handheld Instruments

Reverse-Battery Protection for DC/DC Converter

and Load

High Efficiency: Up to 94%

Generates 5V at 175mA from a 1.8V Input

Operates from 1.8V to 5.5V Input Supply

2V to 6V Adjustable Output Voltage

Inrush Current Controlled During Start-Up

Output Disconnnect in Shutdown

Low Noise 1.2MHz PWM Operation

Tiny External Components

Automatic Burst Mode

Operation (LTC3499)

Continuous Switching at Light Loads (LTC3499B)

Overvoltage Protection

8-Lead (3mm × 3mm × 0.75mm) DFN

and MSOP Packages

4.7µH

3499 TA01

LTC3499

GND

OUT

SHDN

OFFON

10µF

OUT

175mA

1.8V TO 3.2V

324k

0.01µF330pF

100k

2.2µF

Battery Current vs V

AND SW VOLTAGE (V)

–6

–1.0

BATTERY CURRENT (µA)

–2 2–4 0 4

3499 TA01b

–0.5

1.0

0.5

SHDN = 0V

OUT

= 0V

Summary of content (16 pages)

PAGE 1
LTC3499/LTC3499B 750mA Synchronous Step-Up DC/DC Converters with Reverse-Battery Protection FEATURES n n n n n n n n n n n n n DESCRIPTION Reverse-Battery Protection for DC/DC Converter and Load High Efficiency: Up to 94% Generates 5V at 175mA from a 1.8V Input Operates from 1.8V to 5.5V Input Supply 2V to 6V Adjustable Output Voltage Inrush Current Controlled During Start-Up Output Disconnnect in Shutdown Low Noise 1.
PAGE 2
LTC3499/LTC3499B ABSOLUTE MAXIMUM RATINGS (Note 1) VIN to GND...................................................... – 7V to 7V VOUT to GND ............................................... – 0.3V to 7V SW to VOUT .................................................... – 7V to 1V SW to GND DC................................................................ –7V to 7V Pulsed < 100ns............................................ –7V to 8V SHDN to GND..................................................
PAGE 3
LTC3499/LTC3499B ELECTRICAL CHARACTERISTICS The l denotes specifications that apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VIN = 2.4V, VOUT = 5V, SHDN = 2.4V, TA = TJ unless otherwise noted. (Note 3) SYMBOL PARAMETER CONDITIONS MIN IFB FB Input Current VFB = 1.22V IVIN VIN Quiescent Current No Output Load ISD VIN Quiescent Current in Shutdown IBURST TYP MAX UNITS 3 50 nA 300 600 µA SHDN = 0V, VOUT = 0V 0.
PAGE 4
LTC3499/LTC3499B TYPICAL PERFORMANCE CHARACTERISTICS 2-Cell to 5V Efficiency vs Load Current (LTC3499 Only) TA = 25°C, unless otherwise noted. Li-Ion to 5V Efficiency vs Load Current (LTC3499 Only) 2-Cell to 5V Efficiency vs Load Current (LTC3499B Only) 100000 100 100000 90 10000 90 10000 70 100 POWER LOSS VIN = 3.2V VIN = 2.4V VIN = 1.8V 50 0.1 1 POWER LOSS 100 60 10 50 1 VIN = 4.2V VIN = 3.6V VIN = 3V 40 0.1 1000 10 100 LOAD CURRENT (mA) 70 30 0.
PAGE 5
LTC3499/LTC3499B TYPICAL PERFORMANCE CHARACTERISTICS Burst Mode Quiescent Current vs Temperature FB Voltage vs Temperature 1.0 Burst Mode QUIESCENT CURRENT (µA) 1.2220 1.2215 1.2210 1.2205 1.2200 1.2195 1.2190 1.2185 –50 –25 0 50 25 TEMPERATURE (°C) 75 REVERSE-BATTERY CURRENT (µA) 30 1.2225 FB VOLTAGE (V) TA = 25°C, unless otherwise noted. 25 20 15 10 5 0 –50 100 –25 0 25 50 TEMPERATURE (°C) 3499 G09 75 100 0.5 0 –0.5 –1.
PAGE 6
LTC3499/LTC3499B PIN FUNCTIONS SHDN (Pin 1): Shutdown Input for IC. Connect to a voltage greater than 1.2V to enable and a voltage less than 0.2V to disable the LTC3499/LTC3499B. VIN (Pin 2): Input Supply Voltage. The valid operating voltage is between 1.8V to 5.5V. VIN has reverse battery protection. Since the LTC3499/LTC3499B use VIN as the main bias source, bypass with a low ESR ceramic capacitor of at least 2.2µF. SW (Pin 3): Switch Pin. Connect an inductor from VIN to this pin with a value between 2.
PAGE 7
LTC3499/LTC3499B FUNCTIONAL BLOCK DIAGRAM VIN 1.8V TO 5.5V + CIN L 2 REVERSE-BATTERY COMPARATOR + SW ANTI-RING 250Ω 1 = CLOSED 0.7V 3 VIN 1 = CLOSED – – + VOUT – 6.8V VSELECT OV COMPARATOR + + – VOUT 1 = OFF ERROR AMPLIFIER + 6 CFF (OPTIONAL) 1.22V ENABLE PWM LOGIC AND DRIVERS THERMAL SD FB 7 COUT R2 + – SLEEP – VC IZERO 8 CC1 RZ 1.2MHz OSCILLATOR SLOPE COMPENSATION Σ SS CURRENT LIMIT COMPARATOR 1 0.
PAGE 8
LTC3499/LTC3499B OPERATION The LTC3499/LTC3499B provide high efficiency, low noise power for boost applications with output voltages up to 6V. Operation can be best understood by referring to the Functional Block Diagram in Figure 1. The synchronous boost converters are housed in either an 8-lead (3mm × 3mm) DFN or MSOP package and operates at a fixed 1.2MHz. With a 1.
PAGE 9
LTC3499/LTC3499B OPERATION Reverse-Battery Protection Connecting the battery backwards poses a severe problem to most power converters. At a minimum the battery will be quickly discharged. Almost all ICs have an inherent diode from VIN (cathode) to ground (anode) which conducts appreciable current when VIN drops more than 0.7V below ground. Under this condition the integrated circuit will most likely be damaged due to the excessive current draw.
PAGE 10
LTC3499/LTC3499B APPLICATIONS INFORMATION PCB LAYOUT GUIDELINES The high speed operation of the LTC3499/LTC3499B demand careful attention to board layout. Advertised performance will not be achieved with careless layout. Figure 2 shows the recommended component placement. A large copper area will help to lower the chip temperature. Traces carrying high current (SW, VOUT, GND) are kept short. The lead length to the battery should be kept as short as possible.
PAGE 11
LTC3499/LTC3499B APPLICATIONS INFORMATION The ESL (equivalent series inductance) is also an important factor for high frequency converters. Using small surface mount ceramic capacitors, placed as close as possible to VOUT, will minimize ESL. Low ESR capacitors should be used to minimize output voltage ripple. A 4.7µF to 10µF output capacitor is sufficient for most applications and should be placed as close to VOUT as possible.
PAGE 12
LTC3499/LTC3499B APPLICATIONS INFORMATION There is a resultant gain increase with a phase lag which makes it difficult to compensate the loop. At heavy loads the right half plane zero can occur at a relatively low frequency. The loop gain is typically rolled off before the RHP zero frequency. The typical error amp compensation is shown in Figure 3, following the equations for the loop dynamics: 1 fPOLE1 ~ (2 • π • 10e6 • CC1) which is extremely close to DC.
PAGE 13
LTC3499/LTC3499B TYPICAL APPLICATIONS Lithium-Ion to 5V, 350mA Lithium-Ion to 5V Efficiency CIN 2.2µF ×5R ON OFF 90 VIN VOUT 1M VC 100k 330pF 80 LTC3499 SHDN FB SS GND 10000 EFFICIENCY SW VOUT 5V 350mA COUT 10µF ×5R EFFICIENCY (%) + 324k CIN: TAIYO YUDEN X5R JMK212BJ225MD COUT: TAIYO YUDEN X5R JMK212BJ106MD L: COILCRAFT MSS5131-472MLB 1000 70 POWER LOSS 100 60 10 50 VIN = 4.2V VIN = 3.6V VIN = 3V 40 0.01µF POWER LOSS (mW) VIN Li-Ion 3.1V TO 4.2V 100000 100 L 4.7µH 30 0.
PAGE 14
LTC3499/LTC3499B PACKAGE DESCRIPTION DD Package 8-Lead Plastic DFN (3mm × 3mm) (Reference LTC DWG # 05-08-1698 Rev C) R = 0.125 TYP 5 0.40 ± 0.10 8 0.70 ±0.05 3.5 ±0.05 1.65 ±0.05 2.10 ±0.05 (2 SIDES) PACKAGE OUTLINE 0.25 ± 0.05 3.00 ±0.10 (4 SIDES) PIN 1 TOP MARK (NOTE 6) 4 0.25 ± 0.05 0.75 ±0.05 0.200 REF 0.50 BSC 2.38 ±0.05 1.65 ± 0.10 (2 SIDES) 1 (DD8) DFN 0509 REV C 0.50 BSC 2.38 ±0.10 BOTTOM VIEW—EXPOSED PAD 0.00 – 0.
PAGE 15
LTC3499/LTC3499B REVISION HISTORY (Revision history begins at Rev C) REV DATE DESCRIPTION PAGE NUMBER C 3/11 Updated Pin Functions for Pins 4 and 9. 6 Corrected typo in Equation from fRPHZ to fRHPZ. 11 3499fc Information furnished by Linear Technology Corporation is believed to be accurate and reliable. However, no responsibility is assumed for its use.
PAGE 16
LTC3499/LTC3499B TYPICAL APPLICATION Two Cells to 3.3V, 250mA Two Cells to 5V Efficiency 100 L 4.7µH CIN 2.2µF ×5R 90 VIN SW LTC3499 ON OFF 562k VC 100k 330pF SS VOUT 3.3V 250mA VOUT SHDN COUT 10µF ×5R FB GND 332k EFFICIENCY (%) + 80 1000 70 100 60 VIN = 3V VIN = 2.4V VIN = 1.8V 50 40 3499 F06a 10 POWER LOSS 0.01µF CIN: TAIYO YUDEN X5R JMK212BJ225MD COUT: TAIYO YUDEN X5R JMK212BJ106MD L: COILCRAFT MSS5131-472MB 10000 EFFICIENCY 0.