Datasheet

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LTC3455/LTC3455-1

3455fc

1Ω

4.7μF

1μF

10μF

4.7μF

WALL 5V

3.3V, HS

1Ω

4.7μF

USB 5V

249k

4.7μH

80.6k

10pF

10μF

3.3V

0.5A

100k

4.7μH

80.6k

10pF

10μF

1.8V

0.4A

LBO

0.1μF

806k

1.8V

BAT

2.49M

2.49k

1.8V

3455 TA01a

μC

USB

CONTROLLER

SINGLE

CELL Li-ION

3.3V TO 4.2V

1.24k

3.32k

WALLFB

HSI

HSO

MAX

USB

SUSPEND

USBHP

SW2

FB2

SW1

FB1

TIMER

PROG

BAT

GND

CHRG

PBSTAT

RST

MODE

LTC3455/LTC3455-1

ON2

PWRON

HSON

ON/OFF

5.6V

TYPICAL APPLICATION

DESCRIPTION

Dual DC/DC Converter

with USB Power Manager

and Li-Ion Battery Charger

The LTC

3455/LTC3455-1 are complete power manage-

ment solutions for a variety of portable applications.

These devices contain two synchronous step-down

DC/DC converters, a USB power controller, a full-featured

Li-Ion battery charger, a Hot Swap output, a low-battery

indicator, and numerous internal protection features. The

LTC3455/LTC3455-1 provide a small, simple solution for

obtaining power from three different power sources: a

single-cell Li-Ion battery, a USB port, and a wall adapter.

Current drawn from the USB bus is accurately limited

under all conditions. Whenever a USB or a wall adapter

is present, the battery charger is enabled and all internal

power for the device is drawn from the appropriate external

power source. All outputs are discharged to ground during

shutdown to provide complete output disconnect. These

devices are available in a 4mm × 4mm 24-pin exposed-

pad QFN package.

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

Hot Swap is a trademark of Linear Technology Corporation. All other trademarks are the

property of their respective owners. Protected by U.S. Patents including 6522118.

FEATURES

APPLICATIONS

Seamless Transition between Input Power Sources:

Li-Ion Battery, USB, and 5V Wall Adapter

Accurate USB Current Limiting (500mA/100mA)

Two High Efﬁ ciency DC/DC Converters: Up to 96%

Thermal Regulation Maximizes Battery Charge

Rate without Risk of Overheating

Full-Featured Li-Ion Battery Charger with 4.2V Float

Voltage for LTC3455 and 4.1V for LTC3455-1

4.1V Float Voltage (LTC3455-1) Improves Battery Life

and High Temperature Safety Margin

Hot Swap™ Output for SDIO and Memory Cards

Pin-Selectable Burst Mode

Operation

Output Disconnect: All Outputs Discharged to Ground

During Shutdown

Available in a 4mm × 4mm × 0.75mm 24-Pin

QFN Package

Handheld Computers

Digital Cameras

MP3 Players

Efﬁ ciency

LOAD CURRENT (mA)

EFFICIENCY (%)

POWER LOSS (mW)

100

1000

3455 TA01b

BAT

= 3.6V

SWITCHER 1

OUT1

= 1.8V

POWER LOSS FOR

BOTH OUTPUTS

SWITCHER 2

OUT2

= 3.3V

1 10 100 1000

Summary of content (28 pages)

PAGE 1
LTC3455/LTC3455-1 Dual DC/DC Converter with USB Power Manager and Li-Ion Battery Charger DESCRIPTION FEATURES n n n n n n n n n n Seamless Transition between Input Power Sources: Li-Ion Battery, USB, and 5V Wall Adapter Accurate USB Current Limiting (500mA/100mA) Two High Efﬁciency DC/DC Converters: Up to 96% Thermal Regulation Maximizes Battery Charge Rate without Risk of Overheating Full-Featured Li-Ion Battery Charger with 4.2V Float Voltage for LTC3455 and 4.1V for LTC3455-1 4.
PAGE 2
LTC3455/LTC3455-1 ABSOLUTE MAXIMUM RATINGS PIN CONFIGURATION (Note 1) ON2 RST MODE PWRON PBSTAT ON TOP VIEW 24 23 22 21 20 19 FB1 1 18 FB2 PROG 2 17 AO TIMER 3 16 AI 25 CHRG 4 15 HSON USBHP 5 14 HSO SUSPEND 6 VBAT SW2 9 10 11 12 WALLFB 8 VMAX 7 USB 13 HSI SW1 Transient (t < 1ms and Duty Cycle < 1%): VMAX USB Voltages .................................. –0.3V to 7V Steady State: VBAT, VMAX, USB Voltages ........................ –0.3V to 6V SW1, SW2 Voltages ...................
PAGE 3
LTC3455/LTC3455-1 ELECTRICAL CHARACTERISTICS The l denotes the speciﬁcations which apply over the full operating temperature range, otherwise speciﬁcations are at TA = 25°C. VBAT = 3.6V, VMAX = 3.6V, VPWRON = 2V, VON is open, VON2 = 0V, VUSB = 0V, VWALLFB = 0V unless otherwise noted. PARAMETER CONDITIONS ON Pin Pullup Current VON = 1V 2.5 μA PWRON Pin Pulldown Current VPWRON = 1V 2.5 μA ON2 Pin Pulldown Current VON2 = 1V 2.
PAGE 4
LTC3455/LTC3455-1 ELECTRICAL CHARACTERISTICS The l denotes the speciﬁcations which apply over the full operating temperature range, otherwise speciﬁcations are at TA = 25°C. VBAT = 3.6V, VMAX = 3.6V, VPWRON = 2V, VON is open, VON2 = 0V, VUSB = 0V, VWALLFB = 0V unless otherwise noted. PARAMETER CONDITIONS MIN TYP MAX UNITS Hot Swap Output Hot Swap PMOS Switch On-Resistance VHSI = 3.3V Hot Swap PMOS Switch Current Limit VHSI = 3.3V, VHSO = 2.5V 120 0.9 Ω 160 mA HSON Pin Threshold 0.
PAGE 5
LTC3455/LTC3455-1 TYPICAL PERFORMANCE CHARACTERISTICS Feedback Pins (FB1, FB2) and AI Pin Voltage Switching Regulator Oscillator Frequency SWITCHING FREQUENCY (MHz) AI 805 800 FB2 FB1 795 790 785 –50 –25 50 25 75 0 TEMPERATURE (°C) 100 SWITCHER 2 800 1.5 FOR BOTH SWITCHERS 1.0 0.5 0 –50 –25 125 50 25 75 0 TEMPERATURE (°C) 100 3455 G04 USB Pin Current Limit VMAX CURRENT LIMIT (A) 200 100 USBHP = 0V 3.5 3.0 2.5 2.0 1.
PAGE 6
LTC3455/LTC3455-1 TYPICAL PERFORMANCE CHARACTERISTICS Battery Charger Regulation Voltage Battery Charger Recharge Threshold 4.20 3.0 TRICKLE CHARGE THRESHOLD (V) 4.30 Battery Charger Trickle-Charge Threshold 4.15 4.25 LTC3455 VRECHARGE (V) VBAT (V) 4.20 4.15 LTC3455-1 4.10 4.10 LTC3455 4.05 4.00 LTC3455-1 3.95 4.05 4.00 –50 –25 50 25 75 0 TEMPERATURE (°C) 100 3.90 –50 –25 125 50 25 75 0 TEMPERATURE (°C) 3455 G13 2.6 THERMAL CONTROL LOOP IN OPERATION 300 200 100 400 300 200 100 7.5 5.
PAGE 7
LTC3455/LTC3455-1 PIN FUNCTIONS FB1 (Pin 1): Feedback Pin for Switcher 1. Set the output voltage by connecting feedback resistors to this pin. PROG (Pin 2): Charge Current Program and Charge Current Monitor Pin. Connect a resistor, RPROG, from this pin to ground to program battery charge current. IBAT = 1000 • 1.23V / RPROG In all modes the voltage on the PROG pin can be used to measure charge current. PROG has a weak pull-up current source to turn the charger off if the pin is left open.
PAGE 8
LTC3455/LTC3455-1 PIN FUNCTIONS FB2 (Pin 18): Feedback Pin for Switcher 2. Set the output voltage by connecting feedback resistors to this pin. ON2 (Pin 19): Enable Pin for Switcher 2. This pin turns on Switcher 2 only if ON is low or PWRON is high. Switcher 2 cannot be turned on by itself. RST (Pin 20): Reset Pin. This pin is an open-drain output that provides a 200ms reset signal during power-up to initialize a microcontroller. MODE (Pin 21): Burst Mode Enable Pin.
PAGE 9
LTC3455/LTC3455-1 BLOCK DIAGRAM WALL 5V 3.9V – 3.32k USB POWER MANAGER USB USB 5V EXTPWR 1 + + 8 1000 – BATTERY CHARGER 5.6V – 1 REF BATTERY PMOS SWITCH USB CONTROLLER USBHP PROG 0.1μF 2.49k GND VBAT VBAT 3.3V to 4.2V 5 4R 4 CHARGE CONTROL 3 VMAX VMAX 1.23V 10μF 2.41R + CHRG TIMER R – + + – 1k VMAX 10 6 4.7μF 1.23V 1000 + SUSPEND WALLFB 1.24k 1Ω 4.7μF 11 1Ω R 2 25 SWITCHER 1 PWM DRIVER 9 7 SW1 4.7μH 1.8V 2.43M AI 4.
PAGE 10
LTC3455/LTC3455-1 OPERATION The LTC3455/LTC3455-1 are designed to be a complete power management solution for a wide variety of portable systems. The device incorporates two current mode stepdown switching regulators, a full-featured battery charger, a USB power controller, a Hot Swap output, a low-battery comparator (which can also be conﬁgured as an LDO) and numerous protection features into a single package.
PAGE 11
LTC3455/LTC3455-1 APPLICATIONS INFORMATION Operation When No Battery Is Present As long as USB or wall power is available, the LTC3455/ LTC3455-1 will operate with no battery present, a crucial requirement for systems with a removable battery. Keep in mind, however, that if the LTC3455/LTC3455-1 are USB powered and the battery is not present, absence of the battery means that there is no reservoir if the system needs more power than the USB port can supply.
PAGE 12
LTC3455/LTC3455-1 APPLICATIONS INFORMATION USB High Power/Low Power/Suspend Modes There are three basic modes for the USB power manager: high power, low power, and suspend. High power mode allows the LTC3455/LTC3455-1 to draw up to 500mA from the USB port, and is selected by pulling the USBHP pin high. Low power mode reduces the allowable current drawn to 100mA, and is selected by pulling the USBHP pin low.
PAGE 13
LTC3455/LTC3455-1 APPLICATIONS INFORMATION Handling Large Transient Loads when USB Powered Many portable devices have nominal loads that can easily be supported by the USB supply, but they have brief transient loads that can exceed the maximum available USB power. The LTC3455/LTC3455-1 are designed to handle these overloads while drawing as much power as possible from the USB port.
PAGE 14
LTC3455/LTC3455-1 APPLICATIONS INFORMATION Using the VMAX Pin to Power Other Devices Startup and Shutdown when Battery-Powered The VMAX pin can be used to provide power for other devices within the system. This pin is connected to the battery when no external power is available, and it is connected to either the USB bus or the wall adapter when either are available. This ensures that all devices powered from VMAX will always draw power from the best available input power source.
PAGE 15
LTC3455/LTC3455-1 APPLICATIONS INFORMATION LTC3455/LTC3455-1 ON2 19 PBSTAT 23 ON 24 SWITCHER 2 ENABLED PWRON 22 + VBAT 9 SWITCHER 1 ENABLED 3V – + WALLFB 11 1.23V CHARGER ENABLED – + USB 8 3.9V USB POWER CONTROLLER ENABLED – SUSPEND 6 3455 F03 Figure 3. Turn-On Logic Diagram Startup and Shutdown When USB or Wall Powered Whenever USB or wall power is present (as sensed by the USB and WALLFB pins), Switcher 1 and the battery charger will always be enabled.
PAGE 16
LTC3455/LTC3455-1 APPLICATIONS INFORMATION Low or Bad Battery Protection (200ms Timeout) The 200ms reset timer is also used to prevent starting the LTC3455/LTC3455-1 when there is insufﬁcient external power or insufﬁcient battery voltage to regulate the outputs. When ﬁrst turned on, the internal 200ms timer starts.
PAGE 17
LTC3455/LTC3455-1 APPLICATIONS INFORMATION Switching Regulator Inductor Selection Switching Regulator Output Capacitor Selection Many different sizes and shapes of inductors are available from numerous manufacturers. Choosing the right inductor from such a large selection of devices can be overwhelming, but following a few basic guidelines will make the selection process much simpler. To maximize efﬁciency, choose an inductor with a low DC resistance.
PAGE 18
LTC3455/LTC3455-1 APPLICATIONS INFORMATION USB Pin and Wall Adapter Capacitor Selection The USB and wall adapter inputs should be bypassed with a 4.7μF to 10μF capacitor. For some applications, the wall input can be bypassed locally with a lower value (down to 1μF), but only if other bulk capacitance is present. The USB pin should always have at least 4.7μF.
PAGE 19
LTC3455/LTC3455-1 APPLICATIONS INFORMATION Programming Switching Regulator Output Voltage The output voltage for each switching regulator is programmed using a resistor divider from the output connected to the feedback pins (FB1 and FB2): ⎛ R2 ⎞ VOUT = 0.8 V • ⎜ 1 + ⎟ ⎝ R1⎠ Typical values for R1 are in the range of 80k to 400k. VOUT R2 FB1, FB2 1, 18 LTC3455/ LTC3455-1 25 GND R1 3455 F07 Tie the MODE pin to VMAX to always allow automatic Burst Mode operation.
PAGE 20
LTC3455/LTC3455-1 APPLICATIONS INFORMATION Soft-start is accomplished by gradually increasing the peak inductor current for each switcher. This allows each output to rise slowly, helping minimize the battery in-rush current. Figure 10 shows the battery current during startup. A soft-start cycle occurs whenever each switcher ﬁrst turns on, or after a fault condition has occurred (thermal shutdown or UVLO). In-Rush Current Limiting When the LTC3455/LTC3455-1 are battery-powered, an internal 0.
PAGE 21
LTC3455/LTC3455-1 APPLICATIONS INFORMATION Programming Charge Current The maximum charge current is programmed using one external resistor connected between the PROG pin and GND (use the closest 1% resistor value): RPROG = 1000 • 1.23V / IBAT If only USB power is used (no wall adapter), select the RPROG value to be 2.49kΩ (or larger) to set the maximum charge current at 500mA. If a wall adapter is also used, ICHARGE can be programmed up to 1A (with a 1.
PAGE 22
LTC3455/LTC3455-1 APPLICATIONS INFORMATION Battery Charger Thermal Limit CHARGE AND USB CURRENT (mA) An internal thermal limit reduces the charge current if the die temperature attempts to rise above approximately 105°C. This protects the LTC3455/LTC3455-1 from excessive temperature, and allows the user to push the limits of the power handling capability of a given circuit board without risk of damaging the LTC3455/LTC3455-1.
PAGE 23
LTC3455/LTC3455-1 APPLICATIONS INFORMATION pin to GND. Since the charge cycle is terminated only by the charge timer, external charge termination is required when using either of these methods. Use an external NMOS to ﬂoat the PROG pin and disable charging. Constant-current-only mode is a good choice for systems that are always powered by a USB supply or wall adapter, and the charger can be used to charge a super-cap or backup battery.
PAGE 24
LTC3455/LTC3455-1 APPLICATIONS INFORMATION 1 L1 L2 VOUT1 VOUT2 C1 C2 C6 C5 C7 C4 GND GND D1 GND USB VBAT VMAX 5V WALL ADAPTER VIAS TO LOCAL GROUND PLANE. Figure 15.
PAGE 25
LTC3455/LTC3455-1 TYPICAL APPLICATIONS using the battery charger to slowly charge this capacitor (normally using such a large capacitor would result in very large inrush currents). With the TIMER pin tied to 8 USB 5V 1Ω C6 4.7μF 6 5.6V USB CONTROLLER 5 10 C5 10μF VMAX, the battery charger operates in constant-current mode (the voltage-loop and timer function are disabled), so the 4700μF capacitor is always fully charged to the available USB voltage.
PAGE 26
LTC3455/LTC3455-1 TYPICAL APPLICATIONS 8 USB 5V 6 1Ω C6 4.7μF USB 5.6V CONTROLLER 5 10 WALL 5V USB MODE SUSPEND HSON USBHP ON2 PWRON RST VMAX PBSTAT 21 15 19 μC 22 20 23 C5 D1 10μF 1Ω C7 4.7μF 3.32k 1M 4 11 CHRG WALLFB C8, 0.1μF 3 1.24k 2 9 + 1.8V C4 4.7μF ON HSO ON/OFF 24 14 3.3V, HS C3 1μF TIMER 2k PROG 2.49k SINGLE CELL Li-ION 3.3V TO 4.2V 1M LTC3455/LTC3455-1 1k AO VBAT HSI SW2 AI FB2 17 13 12 16 L2, 4.7μH 100pF VMAX M1 FDN304P OR Si2305DS 249k 3.3V 1.
PAGE 27
LTC3455/LTC3455-1 PACKAGE DESCRIPTION UF Package 24-Lead Plastic QFN (4mm × 4mm) (Reference LTC DWG # 05-08-1697) 0.70 ±0.05 4.50 ± 0.05 2.45 ± 0.05 3.10 ± 0.05 (4 SIDES) PACKAGE OUTLINE 0.25 ±0.05 0.50 BSC RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS 4.00 ± 0.10 (4 SIDES) BOTTOM VIEW—EXPOSED PAD 0.75 ± 0.05 R = 0.115 TYP PIN 1 NOTCH R = 0.20 TYP OR 0.35 × 45° CHAMFER 23 24 0.40 ± 0.10 PIN 1 TOP MARK (NOTE 6) 1 2 2.45 ± 0.10 (4-SIDES) (UF24) QFN 0105 0.200 REF 0.00 – 0.05 0.25 ± 0.05 0.
PAGE 28
LTC3455/LTC3455-1 TYPICAL APPLICATION 8 USB 5V 6 1Ω C6 4.7μF 5.6V USB CONTROLLER 5 D1 1Ω C7 4.7μF SUSPEND HSON VMAX PBSTAT 19 μC 22 20 23 1M 1M 1.8V LTC3455/LTC3455-1 1k CHRG 11 WALLFB C8, 0.1μF 3 1.24k ON HSO ON/OFF 24 14 3.3V, HS C3 1μF TIMER 2 PROG 2.49k 9 + PWRON RST 4 SINGLE CELL Li-ION 3.3V TO 4.2V ON2 21 15 C5 10μF 3.32k REMOVE THESE COMPONENTS IF WALL ADAPTER IS NOT USED MODE USBHP 10 WALL 5V USB VBAT C4 4.7μF HSI SW2 FB2 1.8V 13 12 18 L2, 4.