LTC3412 [Linear]
Dual DC/DC Converter with USB Power Manager and Li-Ion Battery Charger; 双通道DC / DC转换器， USB电源管理器和锂离子电池充电器
| 型号： | LTC3412 |
| 厂家： | 
Linear |
| 描述： | Dual DC/DC Converter with USB Power Manager and Li-Ion Battery Charger |
| 文件： | 总24页 (文件大小：516K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
LTC3455
Dual DC/DC Converter
with USB Power Manager
and Li-Ion Battery Charger
U
DESCRIPTIO
FEATURES
The LTC®3455 is a complete power management solution
for a variety of portable applications. The device contains
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 provides a
small, simple solution for obtaining power from three
differentpowersources:asingle-cellLi-Ionbattery, aUSB
port, and a wall adapter. Current drawn from the USB bus
isaccuratelylimitedunderallconditions. WheneveraUSB
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 dis-
charged to ground during shutdown to provide complete
output disconnect. The device is available in a
4mm × 4mm 24-pin exposed-pad QFN package.
■
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
■
■
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 × 0.8mm 24-Pin
QFN Package
U
APPLICATIO S
■
Handheld Computers
Digital Cameras
MP3 Players
, LTC and LT are registered trademarks of Linear Technology Corporation.
■
Hot Swap is a trademark of Linear Technology Corporation.
Burst Mode is a registered trademark of Linear Technology Corporation.
*U.S. Patent 6,522,118
■
U
TYPICAL APPLICATIO
8
21
15
19
22
20
23
USB 5V
1Ω
USB
MODE
HSON
ON2
6
SUSPEND
USB
Efficiency
5
4.7µF
CONTROLLER
µC
USBHP
PWRON
RST
100
10
SWITCHER 2
OUT2
WALL 5V
V
MAX
V
= 3.3V
95
90
85
80
75
70
65
60
PBSTAT
10µF
1Ω
1µF
1M
1M
ON/OFF
LTC3455
3.32k
1k
1.8V
4
SWITCHER 1
V = 1.8V
OUT1
CHRG
24
14
11
ON
WALLFB
0.1µF
3.3V, HS
HSO
3
2
1.24k
1µF
TIMER
PROG
13
12
HSI
2.49k
4.7µH
9
3.3V
0.5A
SW2
V
BAT
10pF
249k
4.7µF
1M
18
7
SINGLE
CELL Li-ION
3.3V TO 4.2V
1.8V
10µF
FB2
+
V
= 3.6V
BAT
80.6k
17
16
LBO
AO
AI
1
10
100
1000
4.7µH
10pF
V
BAT
1.8V
0.4A
SW1
LOAD CURRENT (mA)
2.49M
100k
3455 TA01b
1
10µF
FB1
25
806k
80.6k
GND
3455 TA01a
3455f
1
LTC3455
W W U W
U
W
U
ABSOLUTE AXI U RATI GS
PACKAGE/ORDER I FOR ATIO
(Note 1)
TOP VIEW
ORDER PART
NUMBER
VBAT, VMAX, USB Voltages ...........................–0.3V to 6V
SW1, SW2 Voltages ....................–0.3V to (VMAX+0.3V)
TIMER Voltage.............................–0.3V to (VMAX+0.3V)
PWRON, ON, ON2, HSON Voltages .............–0.3V to 6V
PBSTAT, RST, CHRG, AO Voltages ..............–0.3V to 6V
HSI, HSO Voltages.......................................–0.3V to 6V
MODE, USBHP, SUSPEND Voltages ............–0.3V to 6V
WALLFB, AI, PROG Voltages .......................–0.3V to 2V
FB1, FB2 Voltages........................................–0.3V to 2V
Junction Temperature........................................... 125°C
Operating Temperature Range (Note 2) .. –40°C to 85°C
Storage Temperature Range ................. –65°C to 125°C
24 23 22 21 20 19
LTC3455EUF
FB1
PROG
1
2
3
4
5
6
18 FB2
17
16
AO
AI
TIMER
25
UF PART
MARKING
CHRG
15 HSON
14 HSO
13 HSI
USBHP
SUSPEND
3455
7
8
9 10 11 12
UF PACKAGE
24-LEAD (4mm × 4mm) PLASTIC QFN
TJMAX = 125°C, θJA = 36°C/W, θJC = 2.5°C/W
EXPOSED PAD (PIN 25) IS GND
MUST BE SOLDERED TO PCB
Consult LTC Marketing for parts specified with wider operating temperature ranges.
ELECTRICAL CHARACTERISTICS
The ● 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
3.0
MAX
UNITS
V
Battery Undervoltage Lockout Voltage
Battery Undervoltage Lockout Hysteresis
V
Rising
2.9
3.2
BAT
450
mV
V
Pin Quiescent Current (Note 3)
BAT
Burst Mode, Battery Powered
PWM Mode, Battery Powered
USB Powered
Wall Powered
Shutdown
V
V
V
V
V
= V
= 1V, V
= 5V, Charger Off
= 1V, Not Switching
MODE
110
500
10
10
2
160
800
20
20
4
µA
µA
µA
µA
µA
ON2
= 0V, Not Switching
ON2
MODE
USB
= 1.5V, V
= 4.5V, Charger Off
= 0V
WALL
PWRON
MAX
MAX
= 0V, V
ON Pin Threshold
0.8
0.8
0.8
0.8
1.23
60
1.0
1.0
V
V
PWRON Pin Threshold
ON2 Pin Threshold
1.0
V
MODE Pin Threshold
1.0
V
WALLFB Pin Threshold Voltage
WALLFB Pin Hysteresis
ON Pin Pullup Current
WALLFB Rising
●
1.20
1.26
V
mV
µA
µA
µA
µA
nA
V
V
V
V
V
= 1V
2.5
2.5
2.5
2.5
±1
ON
PWRON Pin Pulldown Current
ON2 Pin Pulldown Current
MODE Pin Pullup Current
WALLFB Pin Input Bias Current
PBSTAT Pin Low Voltage
= 1V
= 1V
PWRON
ON2
= 1V
MODE
= 1.35V
●
±30
WALLFB
V
V
= 0V, I
= 0V, I
= 100µA
= 1mA
0.02
0.20
0.10
0.35
V
V
ON
PBSTAT
PBSTAT
ON
RST Pin Low Voltage
RST Pulse Duration
I
I
= 100µA
= 1mA
0.02
0.20
0.10
0.35
V
V
RST
RST
After FB1 and FB2 in Regulation
200
ms
3455f
2
LTC3455
ELECTRICAL CHARACTERISTICS
VUSB = 0V, VWALLFB = 0V unless otherwise noted.
The ● 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,
PARAMETER
Battery-V
CONDITIONS
MIN
TYP
MAX
UNITS
PMOS
MAX
V
V
V
PMOS Switch On-Resistance
Switch Current Limit
0.15
4.0
Ω
A
MAX
MAX
MAX
2.5
0.4
Switch Current Limit at Startup
With V
Rising, V
= 3V, V = 3.6V
BAT
0.9
A
MAX
MAX
Gain Block
AI Pin Threshold Voltage
AI Pin/FB2 Pin Voltage Difference
AI Pin Input Bias Current
AO Pin Sink Current
●
●
0.784
–8
0.805
0
0.826
8
V
mV
nA
mA
V
V
V
V
V
– V
AI
FB2
= 0.85V
±1
±25
2.5
1.2
AI
AI
AI
= 0.6V, V = 1.5V
1.0
1.8
0.8
AO
AO Pin Voltage
= 0.6V, I = 1mA
AO
Switching Regulators
FB1, FB2 Voltage
●
●
0.784
0.805
0.01
8
0.826
V
%/V
mV
nA
FB1, FB2 Voltage Line Regulation
FB1, FB2 Voltage Burst Mode Hysteresis
FB1, FB2 Pin Input Bias Current
Switching Frequency
V
V
V
= 3V to 5V
MAX
= 2V
MODE
= V = 0.85V
±1
±25
FB1
FB2
Both Switchers
Both Switchers
Both Switchers
1.2
1.5
1.8
MHz
Ω
PMOS Switch On-Resistance
NMOS Switch On-Resistance
PMOS Switch Current Limit
0.35
0.45
Ω
Switcher 1
Switcher 2
450
700
600
900
850
1200
mA
mA
USB Power Manager
USB Undervoltage Lockout Voltage
USB Undervoltage Lockout Hysteresis
USB Minimum Voltage to Charge Battery
USB PMOS Switch On-Resistance
USB Current Limit
From Low to High
3.75
3.90
150
4.0
4.10
V
mV
V
V
= 5V
0.5
Ω
USB
V
V
= 5V, V
= 5V, V
= 2V
= 0V
●
●
440
60
475
80
500
100
mA
mA
USB
USB
USBHP
USBHP
USB Suspend Mode Bias Current
SUSPEND Pin Threshold
V
= 5V, V
= 2V
SUSPEND
4
20
1.1
1.1
µA
V
USB
0.8
0.8
2.5
2.5
USBHP Pin Threshold
V
SUSPEND Pin Pulldown Current
USBHP Pin Pulldown Current
Hot Swap Output
V
V
= 0.5V
µA
µA
SUSPEND
= 0.5V
USBHP
Hot Swap PMOS Switch On-Resistance
Hot Swap PMOS Switch Current Limit
HSON Pin Threshold
V
V
= 3.3V
0.9
160
0.8
2.5
Ω
mA
V
HSI
HSI
= 3.3V, V
= 2.5V
120
HSO
1.1
HSON Pin Pulldown Current
µA
3455f
3
LTC3455
ELECTRICAL CHARACTERISTICS
The ● 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, VON = 0V,
V
USB = 0V, VWALLFB = 0V unless otherwise noted.
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
Battery Charger
Regulated Charger V
Voltage
0°C ≤ T ≤ 85°C
4.158
4.200
4.242
V
BAT
A
Charger Current Limit (USB Powered)
R
R
=2.49kΩ, V
=2.49kΩ, V
= 2V, V
= 0V, V
= 5V, 0°C ≤ T ≤ 85°C
400
50
470
90
mA
mA
PROG
PROG
USBHP
USBHP
USB
USB
A
= 5V, 0°C ≤ T ≤ 85°C
A
Charger Current Limit (Wall Powered)
Recharge Battery Voltage Threshold
Trickle Charge Trip Threshold
Trickle Charge Trip Hysteresis
Trickle Charge Current
R
=2.49kΩ, V
= 4.5V, 0°C ≤ T ≤ 85°C
425
500
150
2.85
60
575
mA
mV
V
PROG
MAX
A
V
– V
RECHARGE
BAT(REGULATED)
Battery Voltage Rising
mV
mA
µA
V
R
=2.49kΩ, V
= 2V
65
PROG
BAT
PROG Pin Current
Internal Pull-Up Current, No R
2
PROG
PROG Pin Voltage
R
=2.49kΩ
1.23
0.75
±10
105
PROG
CHRG
CHRG Pin Output Low Voltage
Timer Accuracy
I
= 5mA
V
C
= 0.1µF
%
TIMER
Junction Temperature in
°C
Constant Temperature Mode
Note 1: Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired.
Note 3: Quiescent current is pulled from the V
pin when neither USB or
BAT
wall power is present, and from the V
pin when either USB or Wall
MAX
power is present.
Note 2: The LTC3455 is guaranteed to meet specified performance from
0°C to 70°C and is designed, characterized and expected to meet these
extended temperature limits, but is not tested at –40°C and 85°C
U W
TYPICAL PERFOR A CE CHARACTERISTICS
Burst Mode Quiescent Current
PWM Mode Quiescent Current
Shutdown Quiescent Current
120
100
80
60
40
20
0
600
500
400
300
200
100
0
5
4
3
2
1
0
V
BAT
= 3.6V
BOTH SWITCHERS ENABLED
BOTH SWITCHERS ENABLED
ONLY SWITCHER 1 ENABLED
ONLY SWITCHER 1 ENABLED
V
= 3.6V
V
= 3.6V
BAT
BAT
NOT SWITCHING
NOT SWITCHING
50
TEMPERATURE (°C)
100 125
50
TEMPERATURE (°C)
100 125
25
50
75
100 125
–50 –25
0
25
75
–50 –25
0
25
75
–50 –25
0
TEMPERATURE (°C)
3455 G01
3455 G02
3455 G03
3455f
4
LTC3455
U W
TYPICAL PERFOR A CE CHARACTERISTICS
Feedback Pins (FB1, FB2)
and AI Pin Voltage
Switching Regulator Oscillator
Frequency
Switching Regulator Current Limit
815
810
805
800
795
790
785
2.0
1.5
1.0
0.5
0
1000
800
600
400
200
0
SWITCHER 2
SWITCHER 1
FOR BOTH SWITCHERS
AI
FB1
FB2
50
TEMPERATURE (°C)
100 125
25
50
TEMPERATURE (°C)
75
100 125
–50 –25
0
25
75
–50 –25
0
50
TEMPERATURE (°C)
75
100 125
–50 –25
0
25
3455 G04
3455 G05
3455 G06
USB Pin Current Limit
VMAX Pin Current Limit
HSO Pin Current Limit
500
400
300
200
100
0
200
150
100
50
5.0
4.5
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0
USBHP = 2V
NORMAL OPERATION
STARTUP
USBHP = 0V
V
V
= 3.3V
= 2.5V
HSI
HSO
V
= 5V
USB
0
50
TEMPERATURE (°C)
–50 –25
0
25
75
100 125
–50 –25
0
25
50
75
100 125
50
TEMPERATURE (°C)
75
100 125
–50 –25
0
25
TEMPERATURE (°C)
3455 G07
3455 G09
3455 G08
Battery Undervoltage Lockout
USB Undervoltage Lockout
WALLFB Trip Voltage
4.00
3.75
3.50
3.25
3.00
2.75
2.50
4.00
3.75
3.50
3.25
3.00
2.75
2.50
1.26
1.24
1.22
1.20
1.18
1.16
1.14
1.12
1.10
RISING
FALLING
RISING
FALLING
RISING
FALLING
50
TEMPERATURE (°C)
100 125
50
TEMPERATURE (°C)
100 125
25
50
75
100 125
–50 –25
0
25
75
–50 –25
0
25
75
–50 –25
0
TEMPERATURE (°C)
3455 G10
3455 G11
3455 G12
3455f
5
LTC3455
U W
TYPICAL PERFOR A CE CHARACTERISTICS
Battery Charger Regulation
Voltage
Battery Charger Recharge
Threshold
Battery Charger Trickle-Charge
Threshold
4.30
4.25
4.20
4.15
4.10
4.05
4.00
3.0
2.9
2.8
2.7
2.6
2.5
4.30
4.25
4.20
4.15
4.10
4.05
4.00
RISING
FALLING
50
TEMPERATURE (°C)
100 125
25
50
75
100 125
–50 –25
0
25
75
–50 –25
0
50
TEMPERATURE (°C)
100 125
–50 –25
0
25
75
TEMPERATURE (°C)
3455 G14
3455 G15
3455 G13
Charge Current When
Wall-Powered
Charge Current When
USB-Powered
Battery Current When
USB- or Wall-Powered
600
500
400
300
200
100
0
600
500
400
300
200
100
0
15.0
12.5
10.0
7.5
5.0
2.5
0
V
V
= 3.6V
= 5V
PROG
V
= 4.2V
BAT
USB
BAT
CHARGER OFF
R
= 2.49k
V
= 2V
USBHP
THERMAL CONTROL
LOOP IN OPERATION
THERMAL CONTROL
LOOP IN OPERATION
V
V
= 3.6V
= 4.5V
PROG
BAT
MAX
R
V
= 0V
USBHP
= 2.49k
50
100 125
50
TEMPERATURE (°C)
100 125
50
0
TEMPERATURE (°C)
100 125
–50 –25
0
25
75
–50 –25
0
25
75
–50 –25
25
75
TEMPERATURE (°C)
3455 G16
3455 G17
3455 G18
PROG Pin Voltage
vs Charge Current
RDS(ON) for Switching Regulator
Power Switches
RDS(ON) for VMAX, USB, and HSO
PMOS Switches
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0
1.50
1.25
1.00
0.75
0.50
0.25
0
V
= 3.6V
V
V
V
= 3.3V
= 5V
V
V
= 3.6V
= 4.5V
= 2.49
BAT
HSI
USB
BAT
BAT
MAX
= 3.6V
R
PROG
= 25°C
T
A
HSO
USB
NMOS
PMOS
V
MAX
50
TEMPERATURE (°C)
100 125
50
100 125
–50 –25
0
25
75
–50 –25
0
25
75
400
100
CHARGE CURRENT (mA)
500
0
200
300
TEMPERATURE (°C)
3455 G20
3455 G21
3455 G19
3455f
6
LTC3455
U
U
U
PI FU CTIO S
FB1 (Pin 1): Feedback Pin for Switcher 1. Set the output
VMAX (Pin 10): Max Voltage Pin. This pin is used to power
the two internal step-down DC/DC converters and is
provided externally to power other devices (i.e. LDOs or
Switchers for LCD bias, white LED backlight drive, etc).
WhentheLTC3455isonandneitherUSBorwallpowerare
available, aninternalPMOSswitchconnectsthispintothe
voltage by connecting feedback resistors to this pin.
PROG (Pin 2): Charge Current Program and Charge Cur-
rent Monitor Pin. Connect a resistor, RPROG, from this pin
to ground to program battery charge current.
IBAT = 1000 • 1.23V / RPROG
V
BAT pin. When either USB or wall power is present, they
provide power to this pin, and the battery charger draws
powerfromthispin. In shutdown, this pin is dischargedto
ground to provide output disconnect.
In all modes the voltage on the PROG pin can be used to
measurechargecurrent. PROGhasaweakpull-upcurrent
source to turn the charger off if the pin is left open.
WALLFB (Pin 11): Wall Power Detection Pin. This pin is
the input to a comparator used to signal the presence of a
5V wall adapter. A resistor divider taken from the wall
adapter input is connected to this pin to tell the LTC3455
when the adapter voltage is high enough to provide power
to the LTC3455. When this pin is higher than 1.23V, the
battery charger is enabled. The 5V wall adapter is con-
nected to the VMAX pin through a Schottky diode. Tie
WALLFB to ground if a wall adapter is not used.
TIMER (Pin 3): Timer Capacitor Pin. Connect a capacitor,
C
TIMER, between this pin and ground to set the charge
cycle termination time. The timer starts when USB or wall
power is first present. The timer period is:
TTIMER (hours) = CTIMER • (3 hours) / (0.1µF)
Tie TIMER to ground to disable just the internal timer
function. Tie TIMER to VMAX to use the charger in a
constant-current-only mode (which disables the timer,
voltage amplifier and trickle charge function).
SW2 (Pin 12): Switch Pin for Switcher 2. Minimize the
length of the metal trace connected to this pin. Place the
inductor for Switcher 2 as close to this pin as possible.
CHRG (Pin 4): Open-Drain Charge Status Pin. This pin is
pulled low with an internal N-channel MOSFET whenever
the battery charger is enabled, and is forced into a high
impedance state whenever it is disabled.
HSI (Pin 13): Hot Swap Input Pin. This pin is connected to
the HSO pin through a current-limited PMOS switch.
USBHP (Pin 5): USB High Power Mode Pin. This pin is
used to select the appropriate USB current limit (either
500mA or 100mA). Pull high to select 500mA (high power
mode); low to select 100mA (low power mode).
HSO(Pin14):HotSwapOutputPin.Thisoutputisusedfor
memory cards or other devices that would appear as a
short if they were hot-plugged directly to one of the
outputs (typically the 3.3V output). The current out of this
pin is limited to 160mA.
SUSPEND (Pin 6): USB Suspend Pin. When this pin is
pulled high, the internal USB power controller is disabled
and the USB pin current reduces to less than 20µA.
HSON(Pin15):HotSwapEnablePin. Thispinturnsonthe
PMOS that connects the HSI and HSO pins.
SW1 (Pin 7): Switch Pin for Switcher 1. Minimize the
length of the metal trace connected to this pin. Place the
inductor for Switcher 1 as close to this pin as possible.
AI (Pin 16): Gain Block Input Pin. This pin is the inverting
input to an amplifier that can be used as a low-battery
detector or as an LDO with the addition of an external PNP
or PMOS. The non-inverting input of the gain block is
connected to the 0.8V internal reference.
USB (Pin 8): USB Supply Pin. Input current into this pin is
limitedtoeither100mAor500mAbasedonthestateofthe
USBHP pin. The charger and Switcher 1 will remain alive
whenever USB power is present (when USB pin is above
3.9V and SUSPEND is low).
AO (Pin 17): Gain Block Output Pin. This pin is an open-
drain output, and is pulled low when the AI pin is less than
800mV. Thisoutputcanbeusedasalow-batterydetector,
orasanLDOwiththeadditionofanexternalPNPorPMOS.
This pin can sink up to 1mA.
VBAT (Pin 9): Battery Input Pin. Bypass this pin with a
capacitor as close to the device as possible.
3455f
7
LTC3455
U
U
U
PI FU CTIO S
FB2 (Pin 18): Feedback Pin for Switcher 2. Set the output
voltage by connecting feedback resistors to this pin.
with the ON and PTSTAT pins, and a momentary-on
switch. Tie PWRON to ground if not used.
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.
PBSTAT (Pin 23): Push-Button Status Pin. This pin is an
open drain output that indicates the state of the ON pin
(which is usually connected to a momentary-on push-
button)tothemicrocontroller. Thispinfollowsthestateof
the ON pin (PBSTAT goes low when ON is pulled low).
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.
ON (Pin 24): ON Pin. Pull this pin to ground to turn on the
LTC3455. This pin is typically used with a momentary-on
push-button switch to turn on the LTC3455. This pin
would be held low until the PWRON pin is pulled high by
a microcontroller to keep the LTC3455 turned on. If a
momentary-on switch is not used, this pin can be held to
ground to keep on the LTC3455. Leave ON open if not
used. This pin has a weak pull-up current source.
MODE (Pin 21): Burst Mode Enable Pin. Tie this pin high
to allow Burst Mode operation for the LTC3455. Burst
Modeoperationwillprovidesuperiorefficiencywhenboth
outputs are operating with very low output currents. Tie
this pin to ground to force PWM operation under all load
current conditions. Burst Mode is disabled initially at
startup (for 200ms) and also whenever external power is
available (even if MODE is pulled high).
GND (Pin 25 – Exposed Pad): Ground Pin. The exposed
backside pad is the only ground pin for the LTC3455 and
must be soldered to the PC board ground plane for the
device to operate properly.
PWRON (Pin 22): Power-On Pin. Pull this pin high to turn
on the LTC3455. This pin is typically used in conjunction
W
W
SI PLIFIED BLOCK DIAGRA
V
IS CONNECTED TO THE BEST
MAX
5V WALL ADAPTER
AVAILABLE INPUT POWER SOURCE
(WALL ADAPTER, USB OR BATTERY)
USB POWER
USB POWER
MANAGER
V
MAX
3.9V TO 5.3V
USE TO POWER OTHER
DC/DCs AND LDOs
BATTERY
Li-Ion BATTERY
SWITCHER 1
SWITCHER 2
HOT SWAP
V
OUT1
PMOS SWITCH
3.3V TO 4.2V
1.8V TYPICAL
BATTERY
CHARGER
V
OUT2
3.3V TYPICAL
USE FOR LDO
OR LOW BATTERY
INDICATOR
GAIN BLOCK
HOT SWAP OUTPUT
3.3V TYPICAL
3455 SBD
3455f
8
LTC3455
W
BLOCK DIAGRA
WALL 5V
3.9V
–
+
3.32k
1Ω
USB POWER MANAGER
1
WALLFB
EXTPWR
USB
11
+
–
USB 5V
8
1000
1µF
1.24k
1Ω
1.23V
BATTERY CHARGER
1
4.7µF
1000
–
REF
BATTERY PMOS SWITCH
V
MAX
+
10
V
MAX
SUSPEND
USBHP
–
+
+
1.23V
6
5
R
10µF
2.41R
USB
CONTROLLER
4R
1k
CHRG
TIMER
PROG
V
4
3
2
MAX
CHARGE
CONTROL
R
0.1µF
2.49k
GND
25
9
SWITCHER 1
4.7µH
SW1
FB1
PWM
DRIVER
V
7
1
1.8V
BAT
V
BAT
3.3V to 4.2V
2.43M
806k
100k
AI
4.7µF
16
10µF
–
80.6k
0.8V
+
AO
ON
ENABLE
LBO
17
–
+
806k
1.8V
0.8V
ON/OFF
SWITCHER 2
24
23
4.7µH
UVLO
SW2
FB2
PWM
DRIVER
V
+
–
BAT
12
18
3.3V
PBSTAT
806k
3.0V
249k
10µF
EXTPWR
1.8V
–
+
80.6k
PWRON
ON2
µC
0.8V
22
19
ENABLE
RST
MODE
HSON
20
21
15
200ms RESET PULSE
BURST MODE ENABLE
HSI
13
14
HOT SWAP
ENABLE
HSO
3.3V, HS
1µF
3455 BD01
3455f
9
LTC3455
U
OPERATIO
seamlessly transitions from battery power (a single-cell
Li-Ion cell) to either the USB supply or a wall adapter. The
battery PMOS switch is turned off, the charger is activated
and all internal power for the device is drawn from the
appropriate external power source. Maximum charge cur-
rent and charge time are programmed using an external
resistor and capacitor, respectively. The USB power man-
ager provides accurate current limiting for the USB pin
under all conditions. The Hot Swap output is ideal for
powering memory cards and other devices that can be
inserted while the system is fully powered.
TheLTC3455isdesignedtobeacompletepowermanage-
ment solution for a wide variety of portable systems. The
device incorporates two current mode step-down switch-
ing regulators, a full-featured battery charger, a USB
power controller, a Hot Swap output, a low-battery com-
parator (which can also be configured as an LDO) and
numerousprotectionfeaturesintoasinglepackage.When
only battery power is available, the battery PMOS switch
connects the VMAX pin to the VBAT pin to provide power to
bothswitchingregulators(andanyotherdevicespowered
from VMAX). When external power is applied, the LTC3455
U
W U U
APPLICATIO S I FOR ATIO
Undervoltage Lockout (UVLO)
Whenever the WALLFB pin is above 1.23V, system power
is drawn from the wall adapter via the VMAX pin, and the
battery charger is active. The 5V wall adapter output is
connected to the VMAX pin through a Schottky diode, and
aresistordividerfromthe5Vwallinputisconnectedtothe
WALLFB pin to signal the LTC3455 that wall power is
present. A higher voltage adapter can also be used, but the
6V maximum rating on the VMAX pin requires the use of an
additional regulator to step down the voltage.
If no external power is present, the LTC3455 will start only
if the battery voltage is above 3.0V. This prevents starting
up with a battery that is too close to deep discharge. Once
started, the battery must drop below 2.6V before the
LTC3455 will shut off. This hysteresis is set intentionally
large to prevent the LTC3455 from turning off at an
inappropriate time, like during the read- or write-cycle of
a hard-disk drive (which could potentially damage the
drive). The internal UVLO is meant only as a last chance
safety measure to prevent running the battery voltage too
low and damaging it. An accurate, user-settable low-
batterythresholdcanbeimplementedusingthegainblock
(see the “Gain Block” section for details) which gives the
microcontroller complete control over the timing of a
shutdown due to a low-battery condition.
If USB power is present and above 3.9V (and wall power
is not available), system power is drawn from the USB pin.
The battery charger is active, but charge current will be
held off until the USB pin increases above 4.0V to prevent
the battery charger from further loading down an already
low USB supply. As long as the USB pin stays above 3.9V,
the USB port supplies all other system power.
If external power is present and the battery voltage is less
than 3.0V, the VMAX pin voltage must be greater than 3.9V
for the LTC3455 to start, and once started, the VMAX pin
must stay above 3.1V for the device to continue running.
If the system needs more power than the USB bus can
supply, the charger turns off completely, the USB power
controller becomes a 500mA (or 100mA) current source
and the VMAX voltage begins to decrease. If VMAX contin-
ues to decrease, eventually the battery will provide the
additional current needed. This allows the LTC3455 to
withstand load current transients that briefly require more
power than the USB power supply can provide.
Selecting the Input Power Source
The priority for supplying power to both DC/DC convert-
ers, all internal circuitry, and the VMAX pin is: Wall adapter,
USB, battery.
3455f
10
LTC3455
U
W U U
APPLICATIO S I FOR ATIO
Operation When No Battery Is Present
desirable, but it is not necessarily an easy task. As the
performanceofdigitalcameras, handheldcomputers, and
MP3 players increases, the power needed to operate them
alsoincreases. ThepoweravailablefromasingleUSBport
(maximum 2.5W) is barely enough to support the peak
power needed by many full-featured portable devices,
even without the power needed to quickly charge their
batteries.
AslongasUSBorwallpowerisavailable, theLTC3455will
operate with no battery present, a crucial requirement for
systemswitharemovablebattery. Keepinmind, however,
that if the LTC3455 is 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. Similarly, if external power is available,
the LTC3455 will operate even if the battery is bad or in
deep-discharge.
To further complicate matters, a USB port is not the ideal
power source. Each device can draw a maximum of
500mA (in high power mode), but the voltage provided to
the portable device can vary quite significantly. Although
a USB power supply has a 5V nominal rating, when you
include normal supply variations, cable losses, and tran-
sient conditions, the USB voltage showing up at the
portable device is typically much lower—often falling to
only 4V. Since the USB port has a strict current limit of
500mA, this means the amount of power available to the
portable device can be as low as 2W. The reduced USB
voltagealsopresentsproblemswhentryingtofullycharge
a single-cell Lithium-Ion battery (that has a 4.2V final
charge voltage) when the USB voltage may itself be below
or near 4.2V.
The LTC3455 is also a good choice for systems that are
always powered by a USB supply or wall adapter. The
charger can then be used to charge a large capacitor or
backup battery, which can briefly provide power to the
system after the external power has been removed. This
gives the microcontroller enough time to follow proper
shutdown procedures even after the main power source is
abruptly removed. If USB powered, the large capacitor or
backup battery will also be used to provide additional
current if the system briefly needs more power than the
USB bus can provide.
Concerns When Wall Adapter Powered
The LTC3455 is specifically designed to alleviate these
problems and make the most of the power the USB port
has to offer. See the sections entitled ”Large Transient
LoadswhenUSBpowered”and”SpecialChargerFeatures
when USB powered” for more detailed discussions of the
LTC3455’s special USB features.
Always choose a wall adapter that can provide power for
all load and battery charging requirements. Choosing a
wall adapter with a power rating that is too small will result
in very long charge times and erratic system operation. If
the total current needed (load and battery charging) ex-
ceeds what the adapter can provide, the voltage on the
VMAX pin will begin to droop. If it droops close enough to
the battery voltage (the VBAT pin), the charge current
decreases and eventually reduces to zero. If the load
current is still too much for the wall adapter to provide, the
wall adapter will provide what it can and the battery will
provide the rest. When wall powered, this operation is
intendedonlyforsurvivingfaultconditionsandshouldnot
be a normal mode of operation.
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 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. The
USBHPpinhasaweakinternalpulldowncurrentsourceto
ensure that the LTC3455 always starts up in USB low
power mode. The SUSPEND pin will disable the USB
power manager completely, reducing the USB pin current
to under 20µA.
Concerns When USB Powered
The popularity of USB (Universal Serial Bus) makes it an
attractive choice for transferring data in a variety of por-
table devices. Therefore, utilizing the USB port to power
these portable devices while charging their battery is very
3455f
11
LTC3455
U
W U U
APPLICATIO S I FOR ATIO
Operation in USB Low Power Mode
The oscilloscope photographs in Figure 1 show how the
LTC3455handlesloadtransientswhenUSBpowered. The
top photo shows a brief transient load that turns off the
charger but does not dip the VMAX voltage. The bottom
photoshowsaprolongedtransientconditionthatturnsoff
the charger and completely dips the VMAX voltage to the
point where the battery must provide current. For both
cases, normal operation resumes as soon as the transient
passes.
Most applications that draw power from the USB bus
should be in low power mode only for a brief amount of
time. All devices must be in low power mode (draw no
more than 100mA of current from the USB bus) upon
power-up, and can transition to high power mode (draw
up to 500mA from the USB bus) only after the device has
beengivenpermissiontodosobytheUSBhostcontroller.
The change to high power mode is usually very quick, so
thefull500mAofcurrentisavailableshortlyafterconnect-
ing to the USB bus. While the LTC3455 will operate when
in low power mode, the amount of power available is so
small that it is difficult or impossible to charge a battery or
even provide enough current to power the rest of the
system. Forthisreason, USBhighpoweroperationshould
always be used with the LTC3455.
Extra capacitance can be connected to the VMAX pin to act
as a reservoir to help support large transient currents. For
most systems this is not necessary, as the LTC3455
cleanly handles heavy transients. For some designs, how-
ever, it may be desirable to use a larger capacitor con-
nected to VMAX to act as a larger reservoir. Up to 50µF of
VMAX
2V/DIV
Handling Large Transient Loads when USB Powered
IMAX
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 is designed to handle these
overloads while drawing as much power as possible from
the USB port. If the USB bus is providing power but the
LTC3455(oranyotherdevicesconnectedtotheVMAX pin)
needs more total power than the USB bus can supply, the
battery charger turns off completely and the USB power
controller becomes a 500mA (or 100mA) current source
and the VMAX voltage begins to decrease. At this point, the
capacitance connected to the VMAX pin provides the addi-
tional current needed by the system. As long as the USB
pin stays above 3.9V, the USB bus will continue to provide
as much current as possible. Once the VMAX pin drops just
below the VBAT voltage, the battery will provide the addi-
tional current needed. This operation allows the LTC3455
to withstand load transients that briefly demand more
power than can be provided by the USB bus.
500mA/DIV
IUSB
500mA/DIV
IBAT
500mA/DIV
3455 F01a
100µs/DIV
USB Maximum Current Condition
VMAX
2V/DIV
IMAX
500mA/DIV
IUSB
500mA/DIV
IBAT
500mA/DIV
3455 F01b
100µs/DIV
USB Heavy Over-Current Condition
Figure 1. Handling Load Transients when USB Powered
3455f
12
LTC3455
U
W U U
APPLICATIO S I FOR ATIO
Startup and Shutdown when Battery-Powered
ceramic capacitance may be connected to the VMAX pin
withoutdifficulty. Morethan50µFrequiresusingacapaci-
tor with some ESR or adding some resistance in series
withsomeoftheceramiccapacitance. Thisisnecessaryto
ensure loop stability in the battery charger loop when
under USB power.
When only battery power is available, the LTC3455 turns
on when either the ON pin is pulled low or the PWRON pin
is pulled high. Either of these pins will keep the device
running, but typically the ON and PWRON pins are used
together to provide turn-on and turn-off using a single
momentary-on push-button switch. Figure 2 shows the
method for using a momentary-on pushbutton to turn the
LTC3455 off and on.
Using the VMAX Pin to Power Other Devices
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.
When the momentary-on switch is first pressed, shorting
the ON pin to ground, PBSTAT goes low and the LTC3455
first brings up the VMAX pin, then enables Switcher 1 to
power the microcontroller. Once up and running, the
microcontroller provides the PWRON signal to keep the
LTC3455 turned on after the push-button is released.
When the push-button is pressed again to turn off the
device, the PBSTAT pin is pulled low to notify the micro-
controller that the push-button has been pressed. The
microcontroller prepares for shutdown then pulls the
PWRONsignallow. Whenthepush-buttonisreleased, the
ON pin goes high and the LTC3455 turns off. The ON and
PWRON pins enable Switcher 1 (along with all the internal
circuits needed for normal operation), and the ON2 pin
enables Switcher 2. Switcher 2 can only operate when
Switcher 1 is also enabled. The turn-on of both switchers
is always delayed until the VMAX pin has reached the VBAT
pin voltage.
The internal PMOS connecting VMAX to the battery is
current limited to 900mA at startup (to minimize in-rush
current) andto4AonceVMAX hasrisenclosetothebattery
voltage. Because of the reduced startup current limit, the
turn-on of other devices powered from VMAX should
alwaysbedelayedtominimizethecurrrentinitiallyneeded
from the VMAX pin. The best choice is to enable these
devices from either switcher output, since the turn-on of
both switchers is always delayed until the VMAX pin has
reached the VBAT pin voltage. The VMAX pin is discharged
to ground when the LTC3455 is shut down, so that any
device supplied by VMAX will have its input grounded
during shutdown. This ensures output disconnect for all
supply voltages within the system.
LTC3455
PBSTAT
23
ON
24
PUSH
BUTTON
µC
SWITCHER 1
ENABLED
PWRON
ON2
22
19
SWITCHER 2
ENABLED
3455 F02
Figure 2. Momentary Push-Button Operation
3455f
13
LTC3455
U
W U U
APPLICATIO S I FOR ATIO
LTC3455
19
23
ON2
PBSTAT
ON 24
SWITCHER 2
ENABLED
PWRON 22
V
9
+
–
BAT
SWITCHER 1
ENABLED
3V
WALLFB 11
+
–
CHARGER
ENABLED
1.23V
USB
8
6
+
–
USB POWER
CONTROLLER
ENABLED
3.9V
SUSPEND
3455 F03
Figure 3. Turn-On Logic Diagram for LTC3455
Startup and Shutdown When USB or Wall Powered
output sequencing when both switchers are enabled at
startup with the ON2 pin tied to VMAX. The turn-on of both
switchersisalwaysdelayeduntiltheVMAX pinhasreached
the VBAT pin voltage.
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. If the LTC3455 is off and
external power is applied, both the charger and Switcher
1 will start independent of the state of the ON and PWRON
pins. This provides maximum battery run-time by always
allowing the battery to charge whenever external power is
available, and ensures that the microcontroller is always
alivewhenexternalpowerisavailable(thisisimportantfor
designs that utilize coulomb-counting or other battery
monitoring techniques). Switcher 2 starts only if ON2 is
also pulled high. Figure 3 shows the turn-on logic diagram
for the LTC3455.
Reset Signal (RST)
A 200ms reset signal (the RST pin is pulled low) is
providedforproperinitializationofamicrocontrollerwhen-
ever the LTC3455 is first turned on, either by the ON or
PWRON pins, or by the application of external power. The
RST signal is also pulled low whenever the LTC3455 is in
shutdown, ensuring no false starts for the microcontroller
as the output voltages are rising or collapsing. In the event
of a fault condition the RST pin will be pulled low.
Starting Switcher 2/Power Supply Sequencing
PWRON/ON2
2V/DIV
Switcher 2 can operate only when Switcher 1 is also
enabled and in regulation. The ON2 pin can be driven by a
logic signal for independent control of Switcher 2. If both
outputs always operate together, tie the ON2 pin to the
VMAX pin. This will enable Switcher 2 after the output of
Switcher 1 has reached 90% of its final value. This power-
up delay ensures proper supply sequencing and reduces
the peak battery current at startup. Figure 4 shows the
VMAX
2V/DIV
VOUT1 (1.8V)
2V/DIV
V
OUT2 (3.3V)
2V/DIV
3455 F04
100µs/DIV
Figure 4. Sequencing for Switcher 1 and 2 Outputs
3455f
14
LTC3455
U
W U U
APPLICATIO S I FOR ATIO
Three good diode choices are the MBRM110E (1A, 10V),
MBR120ESF (1A, 20V), and the MBRA210E (2A, 10V). All
areavailableinverysmallpackagesfromONSemiconduc-
tor (www.onsemi.com), have reverse leakage currents
under 1µA at room temperature, and have forward drops
of around 500mV at their maximum rated current
(1A or 2A).
Low or Bad Battery Protection (200ms Timeout)
The 200ms reset timer is also used to prevent starting the
LTC3455 when there is insufficient external power or
insufficient battery voltage to regulate the outputs. When
first turned on, the internal 200ms timer starts. If only
Switcher 1 is enabled (ON2 is low) and its output does not
reach 90% of its final value within 200ms, Switcher 1 is
shut down even if the ON pin is held low or if the PWRON
pin is held high (the VMAX pin will remain on as long as ON
is low or PWRON is high). This automatic shutdown
feature prevents possible damage to a defective or
overdischarged Li-Ion battery. If ON2 is tied to VMAX so
that Switcher 2 is also turned on at startup, then both
outputsmustreach90%oftheirfinalvalueswithin200ms.
Once the output(s) are in regulation, the timer is reset for
a full 200ms.
V
MAX
10
V
MAX
WALL 5V
LTC3455
I
LEAKAGE
3.32K
11
WALLFB
1.24K
3455 F05
Figure 5. Schottky Leakage Current Path
Schottky Diode Selection/WALLFB Resistor Selection
Switching Regulator General Information
When a 5V wall adapter is used, power is provided to the
VMAX pin through a Schottky diode. The most important
specification in picking this diode is its reverse leakage
current. When the LTC3455 is turned on but wall power is
not present, the Schottky will leak current to ground
through the WALLFB resistor divider (see Figure 5). This
leakagecurrentshouldbeminimized(bypickinganappro-
priate low-leakage Schottky diode) as it can dramatically
reduce Burst Mode efficiency at light loads. In addition, a
high leakage current can also false trip the WALLFB pin
and turn on the LTC3455 even if wall power is not
available. To help prevent this false turn-on, use the
WALLFB resistor values shown in Figure 5.
The LTC3455 contains two 1.5MHz constant-frequency
current mode switching regulators that operate with effi-
ciencies up to 96%. Switcher 1 provides up to 400mA at
1.5V/1.8V(topoweramicrocontrollercore), andSwitcher
2 provides up to 600mA at 3V/3.3V (to power microcon-
troller I/O, memory and other logic circuitry). Both con-
verters support 100% duty cycle operation (low dropout
mode) when the input voltage drops very close to the
output voltage, and both are capable of operating in Burst
Mode operation for highest efficiencies at light loads
(Burst Mode operation is pin selectable). Switcher 2 has
independent ON/OFF control, but operates only when
Switcher 1 is also enabled and in regulation. If both are
enabled at power-up, Switcher 2 is allowed to turn on only
after Switcher 1 has reached 90% of its final value. This
power-up delay ensures proper supply sequencing and
reduces the peak battery current at startup. If the output of
Switcher 1 drops to below 85% of its programmed output
voltage, Switcher 2 will turn off. This ensures that any
problems with the core supply will shut down the rest of
the sytem.
The diode forward voltage drop should be around 500mV
or less at its maximum rated current to allow charging
even when the wall adapter voltage is lower than normal.
Some manufacturers have recently introduced Schottky
diodes optimized for a very low forward drop, but their
reverse leakage currents can be more than 100µA at room
temperature, and over 1mA at high temperatures. These
diodes are not recommended for use with the LTC3455,
but if they are used operation at high temperature should
becheckedthoroughlytoavoidproblemsduetoexcessive
diode leakage current.
3455f
15
LTC3455
U
W U U
APPLICATIO S I FOR ATIO
Switching Regulator Output Capacitor Selection
Switching Regulator Inductor Selection
Low ESR (equivalent series resistance) ceramic capaci-
tors should be used at both switching regulator outputs.
Only X5R or X7R ceramic capacitors should be used
because they retain their capacitance over wider voltage
and temperature ranges than other ceramic types. A 10µF
output capacitor is sufficient for most applications. Table
2showsalistofseveralceramiccapacitormanufacturers.
Consult each manufacturer for detailed information on
their entire selection of ceramic capacitors. Many manu-
facturers now offer very thin (<1mm tall) ceramic capaci-
tors ideal for use in height-restricted designs.
Many different sizes and shapes of inductors are available
from numerous manufacturers. Choosing the right induc-
tor from such a large selection of devices can be over-
whelming, but following a few basic guidelines will make
the selection process much simpler. To maximize effi-
ciency, choose an inductor with a low DC resistance. Keep
inmindthatmostinductorsthatareverythinorhaveavery
small volume typically have much higher core and DCR
losses, and will not give the best efficiency.
Choose an inductor with a DC current rating at least 1.5
timeslargerthanthemaximumloadcurrenttoensurethat
the inductor does not saturate during normal operation.
Table 1 shows several inductors that work well with the
LTC3455. These inductors offer a good compromise in
currentrating, DCRandphysicalsize. Consulteachmanu-
facturerfordetailedinformationontheirentireselectionof
inductors.
Table 2. Recommended Ceramic Capacitor Manufacturers
Taiyo Yuden
AVX
(408) 573-4150
(803) 448-9411
(714) 852-2001
(888) 835-6646
www.t-yuden.com
www.avxcorp.com
www.murata.com
www.tdk.com
Murata
TDK
V
BAT Pin Capacitor Selection
Table 1. Recommended Inductors
Max
Max
DCR
(Ω)
For the VBAT pin, a 4.7µF to 10µF ceramic capacitor is the
best choice. Only X5R or X7R ceramic capacitors should
be used.
Inductor
Type
L
(µH)
I
Height
(mm)
DC
(A)
Manufacturer
DB318C
4.7
10
0.86
0.58
0.1
0.18
1.8
1.8
Toko
(847)297-0070
www.toko.com
VMAX Pin Capacitor Selection
CLS4D09
4.7
10
0.75
0.5
0.19
0.37
1
1
Sumida
(847)956-0666
www.sumida.com
For the VMAX pin, a 10µF ceramic capacitor is the best
choice. Only X5R or X7R ceramic capacitors should be
used. Do not use less than 10µF on this pin. For some
designs it may be desirable to use a larger capacitor
connected to VMAX toact asa reservoir when the LTC3455
is USB powered. Up to 50µF of ceramic capacitance may
be connected to the VMAX pin without difficulty. More than
50µF requires using a capacitor with some ESR (like a
Tantalum or OS-CON) or adding some resistance in series
with some of the ceramic capacitance. This is necessary
to ensure loop stability in the battery charger loop when
under USB power.
CDRH3D16
SD12
4.7
10
0.9
0.55
0.11
0.21
1.8
1.8
Sumida
4.7
10
1.29
0.82
0.12
0.28
1.2
1.2
Cooper
(561)752-5000
www.cooperet.com
ELT5KT
4.7
10
1
0.68
0.2
0.36
1.2
1.2
Panasonic
(408)945-5660
www.panasonic.com
3455f
16
LTC3455
U
W U U
APPLICATIO S I FOR ATIO
USB Pin and Wall Adapter Capacitor Selection
Burst Mode™ Operation
Cautionmustbeexercisedwhenusingceramiccapacitors
to bypass the USB pin or the wall adapter input. High
voltage transients can be generated when the USB or wall
adapter is hot plugged. When power is supplied via the
USB bus or wall adapter, the cable inductance along with
the self resonant and high Q characteristics of ceramic
capacitors can cause substantial ringing which can easily
exceed the maximum voltage pin ratings and damage the
LTC3455.RefertoLinearTechnologyApplicationNote88,
entitled“CeramicInputCapacitorsCanCauseOvervoltage
Transients” for a detailed discussion of this problem. The
long cable lengths of most wall adapters and USB cables
makes them especially susceptible to this problem. Even
ifthisringingisnotlargeenoughtodamagethepart, itcan
couple to the VMAX pin (and to the switching regulator
outputs)andbemistakenasloopinstability.Tobypassthe
USB pin and the wall adapter input, add a 1Ω resistor in
series with a ceramic capacitor to lower the effective Q of
the network and greatly reduce the ringing. A tantalum,
OS-CON, or electrolytic capacitor can be used in place of
the ceramic and resistor, as their higher ESR reduces the
Q, thusreducingthevoltageringing. Use4.7µFto10µFfor
the USB pin, and 1µF or larger for the wall adapter input.
Forhighestefficienciesatlightloads,bothDC/DCconvert-
ers are capable of operating in Burst Mode. In this mode,
energy is delivered to the outputs in shorts bursts, which
minimizesswitchinglossesandquiescent-currentlosses.
Output voltage ripple is slightly higher in this mode, but
efficiency is greatly improved. As shown in Figure 7, the
efficiency at low load currents increases significantly
when Burst Mode operation is used.
100
Burst Mode
3.3V
90
80
1.8V
3.3V
70
Burst
PWM Mode
Mode
60
50
1.8V
PWM Mode
40
30
V
= 3.6V
BAT
20
1
10
100
1000
LOAD CURRENT (mA)
3455 F07
Figure 7. PWM and Burst Mode Efficiency
Tie the MODE pin to VMAX to always allow automatic Burst
Mode operation. Even when the MODE pin is high, the
LTC3455 will only enter Burst Mode when the load current
is low. For many noise-sensitive systems, Burst Mode
operationmightbeundesirableatcertaintimes(i.e.during
a transmit or receive cycle of a wireless device), but highly
desirable at others (i.e. when the device is in low-power
standby mode). The MODE pin can be used to enable or
disable Burst Mode operation at any time, offering both
low-noise and low-power operation when they are needed
themost. BurstModeisdisabledinitiallyatstartup(forthe
first 200ms) and also whenever external power is avail-
able, even if the MODE pin is pulled high.
Programming Switching Regulator Output Voltage
The output voltage for each switching regulator is pro-
grammed using a resistor divider from the output con-
nected to the feedback pins (FB1 and FB2):
R2
VOUT = 0.8V • 1+
R1
Typical values for R1 are in the range of 80k to 400k.
V
OUT
R2
1, 18
25
FB1, FB2
LTC3455
Figure 8 shows the switching waveforms for switcher 1
(both PWM mode and Burst Mode Operation) with VIN =
3.6V, VOUT1 = 1.8V, and IOUT1 = 25mA.
R1
GND
3455 F06
Burst Mode is a registered trademark of Linear Technology Corporation.
Figure 6. Setting the Output Voltage
3455f
17
LTC3455
U
W U U
APPLICATIO S I FOR ATIO
Burst Mode
In-Rush Current Limiting
When the LTC3455 is battery-powered, an internal 0.15Ω
PMOS switch connects the battery (VBAT pin) to the VMAX
pin to provide power for both switchers and other internal
circuitry. ThisPMOSswitchisturnedoffinshutdown, and
the VMAX pin discharges to ground, providing output
disconnectforalloutputs.Atstartup,thisPMOSmustfirst
charge up any capacitance present on the VMAX pin to the
battery voltage. To minimize the in-rush current needed
from the battery, the PMOS switch is current-limited to
900mA and both switchers are disabled while the VMAX
voltage is ramping up. Once VMAX reaches the battery
voltage, the PMOS current-limit increases to 4A and both
switchers are allowed to turn on. Figure 9 shows the
startup battery current for the LTC3455, which stays well-
controlled while VMAX is ramping up and while both
switchers outputs are rising.
VSW1
2V/DIV
VOUT1
50mV/DIV
AC COUPLED
IL1
100mA/DIV
3455 F08a
5µs/DIV
PWM Mode
VSW1
2V/DIV
VOUT1
10mV/DIV
AC COUPLED
IL1
100mA/DIV
3455 F08b
1µs/DIV
Battery Charger General Information
Figure 8. Burst Mode and PWM Mode Waveforms
The battery charger and Switcher 1 will always be enabled
whenever USB or wall power is present (as sensed by the
USB and WALLFB pins). This ensures that the battery can
be charged and that the microcontroller is alive whenever
external power is available. For some applications, it may
be undesirable for the charger to become active immedi-
ately when external power is applied. For such applica-
tions, an NMOS switch can be used to disconnect the
RPROG resistor and allow the PROG pin to float high,
turning off the charger. In this manner, charging occurs
only when allowed by the microcontroller.
Soft-Start for each Switcher
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. Figure9showsthebatterycurrentduringstartup.
A soft-start cycle occurs whenever each switcher first
turns on, or after a fault condition has occurred (thermal
shutdown or UVLO).
The LTC3455 battery charger is a constant-current, con-
stant-voltagecharger.Inconstant-currentmode,themaxi-
mum charge current is set by a single external resistor.
When the battery approaches the final float voltage, the
chargecurrentbeginstodecreaseasthechargerswitches
to constant-voltage mode. The charge cycle is terminated
only by the charge timer.
VMAX
2V/DIV
V
OUT1 (1.8V)
2V/DIV
VOUT2 (3.3V)
2V/DIV
IBAT
500mA/DIV
3455 F09
100µs/DIV
Figure 9. In-Rush Current at Startup
3455f
18
LTC3455
U
W U U
APPLICATIO S I FOR ATIO
Charge and Recharge Cycles
Capacitance on the PROG pin should be minimized to
ensure loop stability when in constant-current mode. Do
notplaceacapacitordirectlyfromthePROGpintoground.
Adding an external R-C network (see Figure 10) allows the
monitoring of average, rather than instantaneous, battery
charge current. Average charge current is typically of
more interest to the user, especially when the LTC3455 is
USB powered, as the battery charge current varies signifi-
cantly with normal load transients.
When external power is first applied, a new charge cycle is
always initiated. The battery will continue charging until
the programmed charge time is reached. If the battery
voltage is below 4.05V at the end of this cycle, the
LTC3455 will start a new charge cycle. This action will
continueuntilthebatteryvoltageexceedsthe4.05Vthresh-
old. This operation is typically seen only when charging
from USB power. Because the charge current can vary
dramatically when the LTC3455 is USB powered, it takes
considerably longer to charge a battery using the USB
supply (as compared to a wall adapter). If the timer
capacitor is chosen correctly, the battery should be fully
charged on one cycle when wall power is available.
LTC3455
CHARGE
10k
2
CURRENT
MONITOR
CIRCUITRY
PROG
R
PROG
C
FILTER
GND
25
If the battery is above the 4.05V threshold when a charge
cycle has expired, charging will stop. At this point, a
recharge cycle is initiated if any of the following occurs:
The battery voltage drops below 4.05V, external power is
removed and reapplied, the PROG pin is floated tempo-
rarily,ortheSUSPENDpinistemporarilypulledhigh(ifthe
LTC3455 is under USB power).
3455 F10
Figure 10. Monitoring Average Charge Current
Programming the Battery Charger Timer
An external capacitor on the TIMER pin sets the total
charge time. When this timer elapses the charge cycle
terminates and the CHRG pin assumes a high impedance
state. The total charge time is programmed as:
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):
TTIMER (hours) = CTIMER • (3 hours) / (0.1µF)
Trickle Charge and Defective Battery Detection
R
PROG = 1000 • 1.23V / IBAT
Ifthebatteryvoltageisbelow2.85Vatthebeginningofthe
charge cycle, the charger goes into trickle charge mode,
reducing the charge current to 10% of its programmed
full-scale value. If the low battery voltage remains for one
quarter of the programmed total charge time, the battery
is assumed to be defective, the charge cycle is terminated,
and the CHRG pin goes to a high impedance state. This
fault is cleared if any of the following occurs: The battery
voltage rises above 2.85V, external power is removed and
reapplied, the PROG pin is floated temporarily, or the
SUSPENDpinistemporarilypulledhigh(iftheLTC3455is
under USB power). The device will still operate normally
from USB or wall power even if the charger has turned off
due to a trickle-charge timeout.
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 1.24kΩ
RPROG value), and the USB power manager will automati-
cally throttle back the charge current to below 500mA
when under USB power.
Monitoring Charge Current
The voltage on the PROG pin is an accurate indication of
the battery charge current under all charging conditions.
IBAT = 1000 • 1.23V / RPROG
3455f
19
LTC3455
U
W U U
APPLICATIO S I FOR ATIO
Battery Charger Thermal Limit
As the USB voltage drops below 4.5V, the charge current
gradually reduces (and eventually shuts off around 4V).
This helps prevent “chattering” and stability problems
when using long, resistive USB cables. Figure 12 shows
this reduction in charge current.
An internal thermal limit reduces the charge current if the
die temperature attempts to rise above approximately
105°C. This protects the LTC3455 from excessive tem-
perature, and allows the user to push the limits of the
power handling capability of a given circuit board without
risk of damaging the LTC3455. Another benefit of the
thermal limit is that charge current can be set according to
typical, not worst-case, ambient temperatures for a given
application with the assurance that the charger will auto-
matically reduce the current under worst-case conditions.
500
USB HIGH POWER MODE
BAT
V
= 3.6V
I
BAT
400
300
200
CHRG Status Output
100
0
The CHRG pin is pulled low with an internal N-channel
MOSFET whenever the battery charger is enabled, and is
forcedintoahighimpedancestatewheneveritisdisabled.
This NMOS device is capable of driving an external LED.
This pin does not provide any C/10 information.
3.75
4.25 4.50 4.75 5.00 5.25
(V)
4.00
V
USB
3455 F12
Figure 12. Charge Current vs USB Voltage
Because the charge current can vary dramatically when
the LTC3455 is USB powered, battery charging can take
considerably longer using the USB supply (as compared
to a wall adapter).
Special Charger Features while USB Powered
The LTC3455 has several special features that help make
the most of the power available from the USB power
supply. The internal USB power controller automatically
throttles back the battery charge current to help keep the Constant-Current-Only Charger/Disabling the
total system current under the strict 500mA/100mA USB Charger Timer
limit. The graph in Figure 11 shows how charge current,
To use the charger in a constant-current-only mode,
I
BAT, decreases as the current needed for the rest of the
connect the TIMER pin to VMAX to disable the timer,
voltage amplifier, and trickle charge function. To disable
only the timer function and leave all others intact, connect
the TIMER pin to GND. Since the charge cycle is termi-
nated only by the charge timer, external charge termina-
tion is required when using either of these methods. Use
an external NMOS to float the PROG pin and disable
charging.
system increases (both switchers and all other external
devices pull current from the VMAX pin). The total USB
current, IUSB, always stays below 500mA.
500
I
USB
400
300
200
100
0
I
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. Disabling the voltage amplifier allows the
super-cap/backup battery to charge up fully to the avail-
able USB or wall adapter voltage.
BAT
USB HIGH POWER MODE
V
V
= 5V
USB
BAT
= 3.6V
–100
0
200
300
400
500 600
100
TOTAL SYSTEM CURRENT (mA)
3455 F11
Figure 11. Charge Current vs Total System Current
3455f
20
LTC3455
U
W U U
APPLICATIO S I FOR ATIO
Hot Swap Output
LOW-BATTERY
DECTECTOR
LDO
1.8V
LBO
3.3V
A current limited Hot Swap output is provided for power-
ing memory cards or other external devices that can be
hot-plugged into the system. Typically connected to the
3.3V supply, this output provides isolation to prevent the
external device from disturbing the 3.3V supply when
inserted. The Hot Swap output can only operate when the
LTC3455 is on, and is enabled using the HSON pin. If this
hot-plugging protection is not needed, this output can be
used as a load switch for other devices within the system.
The HSO pin is discharged to ground when the LTC3455
is shut down.
1M
100k
17
16
17
AO
AO
V
2.5V
100pF
BAT
LTC3455
AI
LTC3455
2.49M
806k
169k
16
AI
10µF
80.6k
3455 F14
Figure 13. Low-Battery Detector and LDO Using the Gain Block
is not a problem for most applications since the LTC3455
usually powers the microcontroller and all other intelli-
gence in the system.
Gain Block
The LTC3455 contains a gain block (pins AI and AO) that
can be used as either a low-battery indicator, or as an LDO
with the addition of an external PNP. Both circuits are
showninFigure13.TheLDOisconvenientforapplications
needing a third output (possibly a low current 2.5V or a
quiet 3V supply). The AO pin can sink around 1mA, which
typically limits the LDO current to 100mA or less (due to
the current gain of the PNP). An external PMOS can be
used for the LDO, but a much larger output capacitor is
needed to ensure stability at light loads.
PCB Layout Considerations
As with all DC/DC converters, careful attention must be
paid to the printed circuit board (PCB) layout and compo-
nent placement. The VBAT capacitor, VMAX capacitor, and
both inductors must all be placed as close as possible to
the LTC3455. These components, along with both DC/DC
converteroutputcapacitors,shouldbeplacedonthesame
side of the circuit board as the LTC3455, with their
connections made on that top layer. Place a local, unbro-
ken ground plane below these components that is tied to
theexposedpadoftheLTC3455.Theexposedpad(pin25)
mustbesolderedtothePCB(tosystemground)forproper
operation.
Thegainblockisalivewheneverswitcher1isenabled, and
is turned off during shutdown to minimize battery drain.
This means that the low-battery detector will not report a
low-battery condition until the LTC3455 is turned on. This
U
TYPICAL APPLICATIO S
Standalone USB Power Supply
with Temporary Backup Power
follow proper shutdown procedures when the main power
sourceisabruptlyremoved. Figure14showsastandalone
power supply for USB high power applications (500mA
maximum USB current) using the LTC3455. The total
system power should be kept below 1.8W to ensure clean
operation even under worst-case USB conditions. With
the resistor values shown, the low-battery indicator (AI
and AO pins) triggers when the VMAX pin voltage drops to
4V, notifying the microcontroller of an impending dropout
condition. The 1MΩ resistor connected between the AI
Although designed primarily for Li-Ion powered portable
applications, the LTC3455 is also a good choice for
systems that are always powered by a USB supply or wall
adapter.Thebatterychargercanthenbeusedtochargeup
a large capacitor or backup battery, which briefly provides
power to the system after the external power has been
removed. This gives the microcontroller enough time to
3455f
21
LTC3455
U
TYPICAL APPLICATIO S
8
6
21
15
19
22
20
23
USB 5V
1Ω
C6
4.7µF
USB
MODE
HSON
ON2
8
6
21
15
19
22
20
23
SUSPEND
USB 5V
1Ω
C6
4.7µF
USB
MODE
HSON
ON2
USB
5
CONTROLLER
SUSPEND
µC
USBHP
USB
PWRON
RST
5
CONTROLLER
µC
USBHP
PWRON
RST
10
WALL 5V
V
MAX
PBSTAT
C5
D1
10
1Ω
C7
1µF
V
MAX
PBSTAT
10µF
1M
1M
ON/OFF
C5
10µF
1.8V
LTC3455
3.32k
1k
1M
1M
ON/OFF
24
14
4
1.8V
LTC3455
CHRG
ON
11
4
WALLFB
3.3V, HS
C3
1µF
1k
24
14
HSO
CHRG
ON
C8, 0.1µF
11
WALLFB
3
2
1.24k
V
MAX
3.3V, HS
C3
1µF
TIMER
PROG
HSO
3
2
M1
TIMER
PROG
V
MAX
17
13
FDN304P
OR
Si2305DS
2.49k
AO
13
12
9
HSI
V
BAT
HSI
2.49k
L2, 4.7µH
C4
4.7µF
L2, 4.7µH
3.3V
0.4A
9
12
16
18
SW2
V
BAT
3.3V
1.2A
SW2
SINGLE
CELL Li-ION
3.3V TO 4.2V
C4
+
10pF
249k
100pF
249k
2.49k
80.6k
4700µF
18
7
C2
10µF
C2
2x10µF
FB2
1.8V
AI
10k
80.6k
17
16
DROPOUT
AO
AI
FB2
L1, 4.7µH
1.8V
0.2A
V
SW1
FB1
MAX
1M
82.5k
10pF
100k
1
C1
10µF
L1, 4.7µH
7
1.8V
0.4A
SW1
25
80.6k
20k
GND
10pF
100k
1
C1
10µF
3455 TA02
C1 TO C8: X5R OR X7R CERAMIC
L1, L2: TOKO DB318C
D1: ON SEMI MBRM110E
ALL RESISTORS 1%
FB1
25
C1, C2, C3, C5, C6: X5R OR X7R CERAMIC
L1, L2: TOKO DB318C
80.6k
GND
3455 F15
ALL RESISTORS 1%
Figure 14. Standalone USB Power Supply with
Temporary Backup Power
Figure 15. LTC3455 Application with 3.3V Output Current
Increased to 1.2A
and AO pins provides 150mV of hysteresis (the dropout
indicator stays low until the VMAX pin rises back above
4.15V). A 4700µF backup capacitor connected to the VBAT
pin briefly provides power to the system after the USB
supply has been removed, and also helps support tran-
sient loads that slightly exceed the USB current limit.
Connecting this large capacitance to the VBAT pin has
several advantages. It provides a large energy reservoir
that is isolated from both the USB pin (the USB specifica-
tion limits capacitance on the USB supply pin to 10µF or
less) and the VMAX pin (using a very large capacitance on
this pin will delay the system turn-on), and it prevents
large inrush currents by 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 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.
Increasing 3.3V Output Current to 1.2A
With an internal current limit of 900mA, Switcher 2 typi-
cally provides a 3.3V, 600mA output. While this output
current is sufficient for many portable devices, some
applicationsneeda3.3Vsupplycapableofprovidingmore
than 1A. Figure 15 shows how to implement a higher
current3.3VoutputusingtheLTC3455.Byaddingonetiny
SOT23PMOSandusingtheAI/AOamplifierasanLDO,the
3.3Voutputnowprovides1.2Aofoutputcurrent.Switcher
2 is programmed for an output voltage of 3.3V, and the
LDO is programmed for an output voltage of 3.2V (3%
lower). As long as the load current is low enough for
Switcher 2 to provide, the LDO is turned off completely.
This circuit is ideal for applications that need the higher
3.3V output current for only a brief time. Switcher 2 will
normallyprovidealloftheoutputcurrent, andtheLDOwill
turn on briefly to provide the higher load currents.
3455f
22
LTC3455
U
TYPICAL APPLICATIO S
VOUT2 (3.3V)
100mV/DIV
When the load current exceeds what Switcher 2 can
provide, the 3.3V output droops slightly and the LDO
provides the additional current needed. Figure 16 shows
the transient response when the 3.3V output current is
stepped from 0.5A to 1.2A. More output capacitance can
be added to improve the 3.3V transient response during
these high current load steps.
AC COUPLED
IOUT2
0.5A/DIV
0.5A TO 1.2A STEP
M1 GATE
2V/DIV
3455 F16
500µs/DIV
Figure 16. Load Current Step (0.5A to 1.2A) for 3.3V Output
U
PACKAGE DESCRIPTIO
UF Package
24-Lead Plastic QFN (4mm × 4mm)
(Reference LTC DWG # 05-08-1697)
0.70 ±0.05
4.50 ± 0.05
3.10 ± 0.05
2.45 ± 0.05
(4 SIDES)
PACKAGE OUTLINE
0.25 ±0.05
0.50 BSC
RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS
BOTTOM VIEW—EXPOSED PAD
0.23 TYP
(4 SIDES)
R = 0.115
TYP
0.75 ± 0.05
4.00 ± 0.10
(4 SIDES)
23 24
PIN 1
TOP MARK
(NOTE 6)
0.38 ± 0.10
1
2
2.45 ± 0.10
(4-SIDES)
(UF24) QFN 1103
0.25 ± 0.05
0.50 BSC
0.200 REF
0.00 – 0.05
NOTE:
1. DRAWING PROPOSED TO BE MADE A JEDEC PACKAGE OUTLINE MO-220 VARIATION (WGGD-X)—TO BE APPROVED
2. DRAWING NOT TO SCALE
3. ALL DIMENSIONS ARE IN MILLIMETERS
4. DIMENSIONS OF EXPOSED PAD ON BOTTOM OF PACKAGE DO NOT INCLUDE
MOLD FLASH. MOLD FLASH, IF PRESENT, SHALL NOT EXCEED 0.15mm ON ANY SIDE, IF PRESENT
5. EXPOSED PAD SHALL BE SOLDER PLATED
6. SHADED AREA IS ONLY A REFERENCE FOR PIN 1 LOCATION
ON THE TOP AND BOTTOM OF PACKAGE
3455f
Information furnished by Linear Technology Corporation is believed to be accurate and reliable.
However, no responsibility is assumed for its use. Linear Technology Corporation makes no represen-
tationthattheinterconnectionofitscircuitsasdescribedhereinwillnotinfringeonexistingpatentrights.
23
LTC3455
TYPICAL APPLICATIO
USB 5V
U
8
6
21
15
19
22
20
23
MODE
HSON
ON2
USB
1Ω
C6
4.7µF
SUSPEND
USB
CONTROLLER
5
µC
USBHP
PWRON
RST
10
WALL 5V
1Ω
V
MAX
PBSTAT
C5
10µF
D1
1M
1M
ON/OFF
C7
1µF
1.8V
LTC3455
3.32k
1k
4
24
14
CHRG
ON
11
REMOVE THESE
COMPONENTS IF
WALL ADAPTER
IS NOT USED
WALLFB
3.3V, HS
C3
1µF
HSO
C8, 0.1µF
3
2
1.24k
TIMER
PROG
13
12
HSI
2.49k
L2, 4.7µH
9
3.3V
0.5A
SW2
V
BAT
C4
4.7µF
10pF
249k
18
7
C2
10µF
SINGLE
CELL Li-ION
3.3V TO 4.2V
FB2
+
1.8V
LBO
1M
80.6k
17
16
AO
AI
L1, 4.7µH
V
1.8V
0.4A
SW1
BAT
2.49M
10pF
100k
1
C1
10µF
FB1
25
80.6k
806k
GND
3455 TA03
C1 TO C8: X5R OR X7R CERAMIC
L1, L2: TOKO DB318C
D1: ON SEMI MBRM110E
ALL RESISTORS 1%
RELATED PARTS
PART NUMBER
DESCRIPTION
COMMENTS
90% Efficiency, V : 3.6V to 25V, V
LT1616
500mA (I ), 1.4MHz, High Efficiency Step-Down
= 1.25V, I = 1.9mA,
Q
OUT
IN
OUT(MIN)
OUT(MIN)
DC/DC Converter
I
<1µA, ThinSOT
SD
LTC1879
1.2A (I ), 550kHz, Synchronous Step-Down
95% Efficiency, V : 2.7V to 10V, V
= 0.8V, I = 15µA,
Q
OUT
IN
DC/DC Converter
I
<1µA, TSSOP16
SD
LTC3405/LTC3405A
LTC3406/LTC3406B
LTC3407
300mA (I ), 1.5MHz, Synchronous Step-Down
DC/DC Converter
95% Efficiency, V : 2.7V to 6V, V
= 0.8V, I = 20µA,
OUT(MIN) Q
OUT
IN
I
<1µA, ThinSOT
SD
600mA (I ), 1.5MHz, Synchronous Step-Down
96% Efficiency, V : 2.5V to 5.5V, V
= 0.6V, I = 20µA,
Q
OUT
IN
OUT(MIN)
OUT(MIN)
OUT(MIN)
DC/DC Converter
I
<1µA, ThinSOT
SD
Dual 600mA (I ), 1.5MHz, Synchronous Step-Down
96% Efficiency, V : 2.5V to 5.5V, V
= 0.6V, I = 40µA,
Q
OUT
IN
DC/DC Converter
I
<1µA, MS10E
SD
LTC3412
2.5A (I ), 4MHz, Synchronous Step-Down
95% Efficiency, V : 2.5V to 5.5V, V
= 0.8V, I = 60µA,
Q
OUT
IN
DC/DC Converter
I
<1µA, TSSOP16E
SD
LTC3414
4A (I ), 4MHz, Synchronous Step-Down
DC/DC Converter
95% Efficiency, V : 2.25V to 5.5V, V
= 0.8V, I = 64µA,
OUT(MIN) Q
OUT
IN
I
<1µA, TSSOP16E
SD
LTC3440/LTC3441
600mA/1A (I ), 2MHz/1MHz, Synchronous Buck-Boost 95% Efficiency, V : 2.5V to 5.5V, V
= 2.5V, I = 25µA/50µA,
OUT
IN
OUT(MIN)
Q
DC/DC Converter
I
<1µA, MS/DFN
SD
3455f
LT/TP 0304 1K • PRINTED IN USA
24 LinearTechnology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
●
●
(408) 432-1900 FAX: (408) 434-0507 www.linear.com
LINEAR TECHNOLOGY CORPORATION 2004
相关型号：
LTC3412AEFE#PBF
LTC3412A - 3A, 4MHz, Monolithic Synchronous Step-Down Regulator; Package: TSSOP; Pins: 16; Temperature Range: -40°C to 85°C
Linear
LTC3412AEFE#TR
LTC3412A - 3A, 4MHz, Monolithic Synchronous Step-Down Regulator; Package: TSSOP; Pins: 16; Temperature Range: -40°C to 85°C
Linear
LTC3412AEFE#TRPBF
LTC3412A - 3A, 4MHz, Monolithic Synchronous Step-Down Regulator; Package: TSSOP; Pins: 16; Temperature Range: -40°C to 85°C
Linear
LTC3412AEUF#TRPBF
LTC3412A - 3A, 4MHz, Monolithic Synchronous Step-Down Regulator; Package: QFN; Pins: 16; Temperature Range: -40°C to 85°C
Linear
©2020 ICPDF网 联系我们和版权申明