LOAD CURRENT (mA)
60
EFFICIENCY (%)
80
75
70
65
85
90
95
100
3455 TA01b
V
BAT
= 3.6V
SWITCHER 1
V
OUT1
= 1.8V
SWITCHER 2
V
OUT2
= 3.3V
1 10 100 1000
查询LTC3411供应商
LTC3455
Dual DC/DC Converter
with USB Power Manager
FEATURES
■
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
and Li-Ion Battery Charger
U
DESCRIPTIO
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
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. The device is available in a
4mm × 4mm 24-pin exposed-pad QFN package.
, 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
TYPICAL APPLICATIO
USB 5V
1Ω
4.7µF
WALL 5V
1Ω
1µF
SINGLE
CELL Li-ION
3.3V TO 4.2V
USB
CONTROLLER
10µF
3.32k
1.24k
1.8V
+
LBO
V
BAT
2.49M
806k
0.1µF
4.7µF
1k
2.49k
1M
10
11
17
16
8
6
5
4
3
2
9
USB
SUSPEND
USBHP
V
MAX
CHRG
WALLFB
TIMER
PROG
V
BAT
AO
AI
LTC3455
U
MODE
HSON
ON2
PWRON
RST
PBSTAT
HSO
HSI
SW2
FB2
SW1
FB1
GND
3455 TA01a
21
15
19
22
20
23
1M
24
ON
14
13
4.7µH
12
10pF
18
4.7µH
7
10pF
1
25
1M
ON/OFF
µC
1.8V
3.3V, HS
1µF
249k
80.6k
100k
80.6k
3.3V
0.5A
10µF
1.8V
0.4A
10µF
Efficiency
3455f
1
LTC3455
242523 22 21 20 19
7 8 9
TOP VIEW
UF PACKAGE
24-LEAD (4mm × 4mm) PLASTIC QFN
10 11 12
6
5
4
3
2
1
13
14
15
16
17
18
FB1
PROG
TIMER
CHRG
USBHP
SUSPEND
FB2
AO
AI
HSON
HSO
HSI
ON
PBSTAT
PWRON
MODE
RST
ON2
SW1
USB
V
BAT
V
MAX
WALLFB
SW2
ABSOLUTE AXI U RATI GS
(Note 1)
V
BAT
SW1, SW2 Voltages ....................–0.3V to (V
TIMER Voltage.............................–0.3V to (V
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
ELECTRICAL CHARACTERISTICS
temperature range, otherwise specifications are at TA = 25°C. V
V
USB
PARAMETER CONDITIONS MIN TYP MAX UNITS
Battery Undervoltage Lockout Voltage V
Battery Undervoltage Lockout Hysteresis 450 mV
V
BAT
Burst Mode,
PWM Mode, Battery Powered V
USB Powered V
Wall Powered V
Shutdown V
ON Pin Threshold 0.8 1.0 V
PWRON Pin Threshold 0.8 1.0 V
ON2 Pin Threshold 0.8 1.0 V
MODE Pin Threshold 0.8 1.0 V
WALLFB Pin Threshold Voltage WALLFB Rising ● 1.20 1.23 1.26 V
WALLFB Pin Hysteresis 60 mV
ON Pin Pullup Current VON = 1V 2.5 µA
PWRON Pin Pulldown Current V
ON2 Pin Pulldown Current V
MODE Pin Pullup Current V
WALLFB Pin Input Bias Current V
PBSTAT Pin Low Voltage VON = 0V, I
RST Pin Low Voltage I
RST Pulse Duration After FB1 and FB2 in Regulation 200 ms
2
, V
, USB Voltages ...........................–0.3V to 6V
MAX
= 0V, V
Pin Quiescent Current (Note 3)
= 0V unless otherwise noted.
WALLFB
Battery Powered V
WW
W
U
UUW
PACKAGE/ORDER I FOR ATIO
ORDER PART
+0.3V)
MAX
+0.3V)
MAX
T
= 125°C, θJA = 36°C/W, θJC = 2.5°C/W
JMAX
EXPOSED PAD (PIN 25) IS GND
MUST BE SOLDERED TO PCB
Consult LTC Marketing for parts specified with wider operating temperature ranges.
The ● denotes the specifications which apply over the full operating
= 3.6V, V
BAT
Rising 2.9 3.0 3.2 V
BAT
= V
ON2
= 1V, V
ON2
= 5V, Charger Off 10 20 µA
USB
WALL
PWRON
PWRON
= 1V 2.5 µA
ON2
MODE
WALLFB
= 0V, I
V
ON
= 100µA 0.02 0.10 V
RST
= 1mA 0.20 0.35 V
I
RST
= 1V, Not Switching 110 160 µA
MODE
= 1.5V, V
= 0V, V
= 0V, Not Switching 500 800 µA
MODE
= 4.5V, Charger Off 10 20 µA
MAX
= 0V 2 4 µA
MAX
= 1V 2.5 µA
= 1V 2.5 µA
= 1.35V ● ±1 ±30 nA
= 100µA 0.02 0.10 V
PBSTAT
= 1mA 0.20 0.35 V
PBSTAT
= 3.6V, V
MAX
PWRON
= 2V, V
is open, V
ON
NUMBER
LTC3455EUF
UF PART
MARKING
3455
ON2
= 0V,
3455f
LTC3455
ELECTRICAL CHARACTERISTICS
temperature range, otherwise specifications are at TA = 25°C. V
V
USB
= 0V, V
= 0V unless otherwise noted.
WALLFB
The ● denotes the specifications which apply over the full operating
= 3.6V, V
BAT
= 3.6V, V
MAX
PWRON
= 2V, V
is open, V
ON
ON2
= 0V,
PARAMETER CONDITIONS MIN TYP MAX UNITS
Battery-V
V
MAX
V
MAX
V
MAX
PMOS
MAX
PMOS Switch On-Resistance 0.15 Ω
Switch Current Limit 2.5 4.0 A
Switch Current Limit at Startup With V
MAX
Rising, V
MAX
= 3V, V
= 3.6V 0.4 0.9 A
BAT
Gain Block
AI Pin Threshold Voltage ● 0.784 0.805 0.826 V
AI Pin/FB2 Pin Voltage Difference V
FB2
– V
AI
–8 0 8 mV
AI Pin Input Bias Current VAI = 0.85V ● ±1 ±25 nA
AO Pin Sink Current VAI = 0.6V, VAO = 1.5V 1.0 1.8 2.5 mA
AO Pin Voltage VAI = 0.6V, IAO = 1mA 0.8 1.2 V
Switching Regulators
FB1, FB2 Voltage ● 0.784 0.805 0.826 V
FB1, FB2 Voltage Line Regulation V
FB1, FB2 Voltage Burst Mode Hysteresis V
FB1, FB2 Pin Input Bias Current V
= 3V to 5V 0.01 %/V
MAX
= 2V 8 mV
MODE
= V
FB1
= 0.85V ● ±1 ±25 nA
FB2
Switching Frequency Both Switchers 1.2 1.5 1.8 MHz
PMOS Switch On-Resistance Both Switchers 0.35 Ω
NMOS Switch On-Resistance Both Switchers 0.45 Ω
PMOS Switch Current Limit Switcher 1 450 600 850 mA
Switcher 2 700 900 1200 mA
USB Power Manager
USB Undervoltage Lockout Voltage From Low to High 3.75 3.90 4.10 V
USB Undervoltage Lockout Hysteresis 150 mV
USB Minimum Voltage to Charge Battery 4.0 V
USB PMOS Switch On-Resistance V
USB Current Limit V
USB Suspend Mode Bias Current V
= 5V 0.5 Ω
USB
V
USB
USB
USB
= 5V, V
= 5V, V
= 5V, V
= 2V ● 440 475 500 mA
USBHP
= 0V ● 60 80 100 mA
USBHP
= 2V 4 20 µA
SUSPEND
SUSPEND Pin Threshold 0.8 1.1 V
USBHP Pin Threshold 0.8 1.1 V
SUSPEND Pin Pulldown Current V
USBHP Pin Pulldown Current V
= 0.5V 2.5 µA
SUSPEND
= 0.5V 2.5 µA
USBHP
Hot Swap Output
Hot Swap PMOS Switch On-Resistance V
Hot Swap PMOS Switch Current Limit V
= 3.3V 0.9 Ω
HSI
= 3.3V, V
HSI
= 2.5V 120 160 mA
HSO
HSON Pin Threshold 0.8 1.1 V
HSON Pin Pulldown Current 2.5 µA
3455f
3
LTC3455
TEMPERATURE (°C)
–50
QUIESCENT CURRENT (µA)
5
4
3
2
1
0
25 75
3455 G03
–25 0
50 100 125
V
BAT
= 3.6V
ELECTRICAL CHARACTERISTICS
temperature range, otherwise specifications are at TA = 25°C. V
V
USB
= 0V, V
= 0V unless otherwise noted.
WALLFB
The ● denotes the specifications which apply over the full operating
= 3.6V, V
BAT
= 3.6V, V
MAX
PWRON
= 2V, V
is open, VON = 0V,
ON
PARAMETER CONDITIONS MIN TYP MAX UNITS
Battery Charger
Regulated Charger V
Charger Current Limit (USB Powered) R
Charger Current Limit (Wall Powered) R
Recharge Battery Voltage Threshold V
Voltage 0°C ≤ TA ≤ 85°C 4.158 4.200 4.242 V
BAT
=2.49kΩ, V
PROG
=2.49kΩ, V
R
PROG
=2.49kΩ, V
PROG
BAT(REGULATED)
= 2V, V
USBHP
= 0V, V
USBHP
= 4.5V, 0°C ≤ TA ≤ 85°C 425 500 575 mA
MAX
– V
RECHARGE
= 5V, 0°C ≤ TA ≤ 85°C 400 470 mA
USB
= 5V, 0°C ≤ TA ≤ 85°C5090mA
USB
150 mV
Trickle Charge Trip Threshold Battery Voltage Rising 2.85 V
Trickle Charge Trip Hysteresis 60 mV
Trickle Charge Current R
PROG Pin Current Internal Pull-Up Current, No R
PROG Pin Voltage R
CHRG Pin Output Low Voltage I
Timer Accuracy C
=2.49kΩ, V
PROG
=2.49kΩ 1.23 V
PROG
= 5mA 0.75 V
CHRG
= 0.1µF ±10 %
TIMER
= 2V 65 mA
BAT
PROG
2 µA
Junction Temperature in 105 °C
Constant Temperature Mode
Note 1: Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired.
Note 2: The LTC3455 is guaranteed to meet specified performance from
Note 3: Quiescent current is pulled from the V
wall power is present, and from the V
pin when either USB or Wall
MAX
power is present.
pin when neither USB or
BAT
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
UW
TYPICAL PERFOR A CE CHARACTERISTICS
Burst Mode Quiescent Current PWM Mode Quiescent Current Shutdown Quiescent Current
120
100
80
60
40
QUIESCENT CURRENT (µA)
20
V
= 3.6V
BAT
NOT SWITCHING
0
–50
–25 0
BOTH SWITCHERS ENABLED
ONLY SWITCHER 1 ENABLED
50 100 125
25 75
TEMPERATURE (°C)
3455 G01
600
500
400
300
200
QUIESCENT CURRENT (µA)
100
0
–50
V
= 3.6V
BAT
NOT SWITCHING
–25 0
TEMPERATURE (°C)
BOTH SWITCHERS ENABLED
ONLY SWITCHER 1 ENABLED
50 100 125
25 75
3455 G02
3455f
4
UW
TEMPERATURE (°C)
–50
HSO PIN CURRENT LIMIT (mA)
200
150
100
50
0
25 75
3455 G09
–25 0
50 100 125
V
HSI
= 3.3V
V
HSO
= 2.5V
TEMPERATURE (°C)
–50
CURRENT LIMIT (mA)
1000
800
600
400
200
0
25 75
3455 G06
–25 0
50 100 125
SWITCHER 1
SWITCHER 2
TEMPERATURE (°C)
–50
WALLFB TRIP VOLTAGE (V)
1.26
1.24
1.22
1.20
1.18
1.16
1.14
1.12
1.10
25 75
3455 G12
–25 0
50 100 125
FALLING
RISING
TYPICAL PERFOR A CE CHARACTERISTICS
LTC3455
Feedback Pins (FB1, FB2)
and AI Pin Voltage
815
810
805
800
VOLTAGE (mV)
795
790
785
–50
–25 0
FB2
TEMPERATURE (°C)
AI
FB1
50 100 125
25 75
3455 G04
USB Pin Current Limit V
500
USBHP = 2V
400
300
200
USB PIN CURRENT (mA)
100
0
–50
V
USB
–25 0
= 5V
USBHP = 0V
50 100 125
25 75
TEMPERATURE (°C)
3455 G07
Switching Regulator Oscillator
Frequency Switching Regulator Current Limit
2.0
1.5
1.0
0.5
SWITCHING FREQUENCY (MHz)
0
–50
5.0
4.5
4.0
3.5
3.0
2.5
2.0
CURRENT LIMIT (A)
1.5
MAX
V
1.0
0.5
0
–50
FOR BOTH SWITCHERS
50 100 125
–25 0
Pin Current Limit HSO Pin Current Limit
MAX
STARTUP
–25 0
25 75
TEMPERATURE (°C)
NORMAL OPERATION
50 100 125
25 75
TEMPERATURE (°C)
3455 G05
3455 G08
Battery Undervoltage Lockout USB Undervoltage Lockout WALLFB Trip Voltage
4.00
3.75
3.50
3.25
3.00
BATTERY UVLO (V)
2.75
2.50
–50
–25 0
RISING
FALLING
50 100 125
25 75
TEMPERATURE (°C)
3455 G10
4.00
3.75
3.50
3.25
USB UVLO (V)
3.00
2.75
2.50
–50
–25 0
RISING
TEMPERATURE (°C)
FALLING
50 100 125
25 75
3455 G11
3455f
5
LTC3455
TEMPERATURE (°C)
–50
BATTERY CURRENT (µA)
15.0
10.0
5.0
12.5
7.5
2.5
0
25 75
3455 G18
–25 0
50 100 125
V
BAT
= 4.2V
CHARGER OFF
TEMPERATURE (°C)
–50
R
DS(ON)
1.4
1.2
1.0
0.8
0.6
0.2
0.4
0
25 75
3455 G21
–25 0
50 100 125
HSO
USB
V
MAX
V
HSI
= 3.3V
V
USB
= 5V
V
BAT
= 3.6V
TEMPERATURE (°C)
–50
TRICKLE CHARGE THRESHOLD (V)
3.0
2.9
2.8
2.7
2.6
2.5
25 75
3455 G15
–25 0
50 100 125
FALLING
RISING
UW
TYPICAL PERFOR A CE CHARACTERISTICS
Battery Charger Regulation
Voltage
4.30
4.25
4.20
(V)
4.15
BAT
V
4.10
4.05
4.00
–50
–25 0
25 75
TEMPERATURE (°C)
Charge Current When
Wall-Powered
600
500
400
THERMAL CONTROL
LOOP IN OPERATION
300
50 100 125
3455 G13
Battery Charger Recharge
Threshold
4.30
4.25
4.20
(V)
4.15
RECHARGE
V
4.10
4.05
4.00
–50
–25 0
25 75
TEMPERATURE (°C)
Charge Current When
USB-Powered
600
V
= 3.6V
BAT
= 5V
V
USB
= 2.49k
R
500
PROG
400
THERMAL CONTROL
LOOP IN OPERATION
300
V
50 100 125
= 2V
USBHP
Battery Charger Trickle-Charge
Threshold
3455 G14
Battery Current When
USB- or Wall-Powered
200
V
= 3.6V
100
BAT
BATTERY CHARGE CURRENT (mA)
0
–50
V
MAX
R
PROG
–25 0
= 4.5V
= 2.49k
PROG Pin Voltage
vs Charge Current
1.50
V
= 3.6V
BAT
V
= 4.5V
MAX
= 2.49
R
1.25
PROG
= 25°C
T
A
1.00
(V)
0.75
PROG
V
0.50
0.25
0
0
100 200
50 100 125
25 75
TEMPERATURE (°C)
300
CHARGE CURRENT (mA)
3455 G16
400 500
3455 G19
200
100
BATTERY CHARGE CURRENT (mA)
0
–50
–25 0
R
DS(ON)
V
USBHP
25 75
TEMPERATURE (°C)
for Switching Regulator
Power Switches
0.7
V
= 3.6V
BAT
0.6
0.5
0.4
DS(ON)
R
0.3
0.2
0.1
0
–50
–25 0
NMOS
PMOS
25 75
TEMPERATURE (°C)
= 0V
50 100 125
3455 G17
50 100 125
3455 G20
R
for V
DS(ON)
MAX
PMOS Switches
, USB, and HSO
3455f
6
UUU
PI FU CTIO S
LTC3455
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, R
to ground to program battery charge current.
I
= 1000 • 1.23V / R
BAT
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.
TIMER (Pin 3): Timer Capacitor Pin. Connect a capacitor,
C
cycle termination time. The timer starts when USB or wall
power is first present. The timer period is:
Tie TIMER to ground to disable just the internal timer
function. Tie TIMER to V
constant-current-only mode (which disables the timer,
voltage amplifier and trickle charge function).
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.
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).
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.
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.
USB (Pin 8): USB Supply Pin. Input current into this pin is
limited to either 100mA or 500mA based on the state of the
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).
V
capacitor as close to the device as possible.
, between this pin and ground to set the charge
TIMER
T
(hours) = C
TIMER
(Pin 9): Battery Input Pin. Bypass this pin with a
BAT
PROG
• (3 hours) / (0.1µF)
TIMER
to use the charger in a
MAX
, from this pin
PROG
V
(Pin 10): Max Voltage Pin. This pin is used to power
MAX
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).
When the LTC3455 is on and neither USB or wall power are
available, an internal PMOS switch connects this pin to the
V
pin. When either USB or wall power is present, they
BAT
provide power to this pin, and the battery charger draws
power from this pin. In shutdown, this pin is discharged to
ground to provide output disconnect.
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 connected to the V
WALLFB to ground if a wall adapter is not used.
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.
HSI (Pin 13): Hot Swap Input Pin. This pin is connected to
the HSO pin through a current-limited PMOS switch.
HSO (Pin 14): Hot Swap Output Pin. This output is used for
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.
HSON (Pin 15): Hot Swap Enable Pin. This pin turns on the
PMOS that connects the HSI and HSO pins.
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.
AO (Pin 17): Gain Block Output Pin. This pin is an opendrain output, and is pulled low when the AI pin is less than
800mV. This output can be used as a low-battery detector,
or as an LDO with the addition of an external PNP or PMOS.
This pin can sink up to 1mA.
pin through a Schottky diode. Tie
MAX
3455f
7
LTC3455
PI FU CTIO S
UUU
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. Tie this pin high
to allow Burst Mode operation for the LTC3455. Burst
Mode operation will provide superior efficiency when both
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).
PWRON (Pin 22): Power-On Pin. Pull this pin high to turn
on the LTC3455. This pin is typically used in conjunction
with the ON and PTSTAT pins, and a momentary-on
switch. Tie PWRON to ground if not used.
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 pushbutton) to the microcontroller. This pin follows the state of
the ON pin (PBSTAT goes low when ON is pulled low).
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.
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.
SI PLIFIEDWBLOCK DIAGRA
USB POWER
3.9V TO 5.3V
Li-Ion BATTERY
3.3V TO 4.2V
USE FOR LDO
OR LOW BATTERY
INDICATOR
USB POWER
MANAGER
BATTERY
PMOS SWITCH
BATTERY
CHARGER
GAIN BLOCK
W
V
IS CONNECTED TO THE BEST
MAX
AVAILABLE INPUT POWER SOURCE
(WALL ADAPTER, USB OR BATTERY)
SWITCHER 1
SWITCHER 2
HOT SWAP
3455 SBD
5V WALL ADAPTER
V
MAX
USE TO POWER OTHER
DC/DCs AND LDOs
V
OUT1
1.8V TYPICAL
V
OUT2
3.3V TYPICAL
HOT SWAP OUTPUT
3.3V TYPICAL
8
3455f
BLOCK DIAGRA
USB
1Ω
4.7µF
SUSPEND
USBHP
CHRG
TIMER
PROG
GND
V
806k
1.8V
PBSTAT
806k
1.8V
PWRON
ON2
MODE
HSON
BAT
RST
8
6
5
4
3
2
25
9
AI
16
AO
17
ON
24
23
22
19
20
21
15
200ms RESET PULSE
BURST MODE ENABLE
CONTROLLER
V
MAX
V
3.3V to 4.2V
µC
USB 5V
USB
1k
0.1µF
2.49k
BAT
2.43M
4.7µF
806k
LBO
ON/OFF
W
USB POWER MANAGER
1 1000
–
REF
+
R
4R
V
+
BAT
3.0V
–
LTC3455
WALL 5V
3.9V
–
+
BATTERY CHARGER
1 1000
–
1.23V
+
2.41R
EXTPWR
BATTERY PMOS SWITCH
+
1.23V
–
11
10
3.32k
WALLFB
1.24k
V
MAX
+
–
PWM
DRIVER
ENABLE
PWM
DRIVER
ENABLE
HOT SWAP
+
SWITCHER 1
SWITCHER 2
4.7µH
SW1
7
100k
FB1
0.8V
0.8V
3455 BD01
1
80.6k
4.7µH
SW2
12
249k
FB2
18
80.6k
HSI
13
HSO
14
–
+
–
+
CHARGE
CONTROL
R
–
0.8V
+
UVLO
EXTPWR
ENABLE
1Ω
1µF
10µF
10µF
10µF
1µF
V
MAX
1.8V
3.3V, HS
3.3V
3455f
9
LTC3455
OPERATIO
U
The LTC3455 is designed to be a complete power management solution for a wide variety of portable systems. The
device incorporates two current mode step-down 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. When
only battery power is available, the battery PMOS switch
connects the V
both switching regulators (and any other devices powered
from V
). When external power is applied, the LTC3455
MAX
pin to the V
MAX
pin to provide power to
BAT
U
WUU
APPLICATIO S I FOR ATIO
Undervoltage Lockout (UVLO)
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 lowbattery threshold can be implemented using the gain block
(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.
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 current and charge time are programmed using an external
resistor and capacitor, respectively. The USB power manager 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.
Whenever the WALLFB pin is above 1.23V, system power
is drawn from the wall adapter via the V
battery charger is active. The 5V wall adapter output is
connected to the V
a resistor divider from the 5V wall input is connected to the
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 V
additional regulator to step down the voltage.
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.
pin through a Schottky diode, and
MAX
pin requires the use of an
MAX
pin, and the
MAX
If external power is present and the battery voltage is less
than 3.0V, the V
for the LTC3455 to start, and once started, the V
must stay above 3.1V for the device to continue running.
Selecting the Input Power Source
The priority for supplying power to both DC/DC converters, all internal circuitry, and the V
USB, battery.
pin voltage must be greater than 3.9V
MAX
pin is: Wall adapter,
MAX
MAX
pin
10
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 V
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.
voltage begins to decrease. If V
MAX
MAX
contin-
3455f
LTC3455
U
WUU
APPLICATIO S I FOR ATIO
Operation When No Battery Is Present
As long as USB or wall power is available, the LTC3455 will
operate with no battery present, a crucial requirement for
systems with a removable battery. Keep in mind, 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.
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
desirable, but it is not necessarily an easy task. As the
performance of digital cameras, handheld computers, and
MP3 players increases, the power needed to operate them
also increases. The power available from a single USB port
(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.
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 transient 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
voltage also presents problems when trying to fully charge
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.
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) exceeds what the adapter can provide, the voltage on the
V
pin will begin to droop. If it droops close enough to
MAX
the battery voltage (the V
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
intended only for surviving fault conditions and should not
be a normal mode of operation.
Concerns When USB Powered
The popularity of USB (Universal Serial Bus) makes it an
attractive choice for transferring data in a variety of portable devices. Therefore, utilizing the USB port to power
these portable devices while charging their battery is very
pin), the charge current
BAT
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
Loads when USB powered” and ”Special Charger Features
when USB powered” for more detailed discussions of the
LTC3455’s special USB features.
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
USBHP pin has a weak internal pulldown current source to
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.
3455f
11
LTC3455
U
WUU
APPLICATIO S I FOR ATIO
Operation in USB Low Power Mode
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
been given permission to do so by the USB host controller.
The change to high power mode is usually very quick, so
the full 500mA of current is available shortly after connecting 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. For this reason, USB high power operation should
always be used with the LTC3455.
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 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 (or any other devices connected to the V
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 V
capacitance connected to the V
voltage begins to decrease. At this point, the
MAX
pin provides the addi-
MAX
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 V
below the V
voltage, the battery will provide the addi-
BAT
pin drops just
MAX
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.
MAX
pin)
The oscilloscope photographs in Figure 1 show how the
LTC3455 handles load transients when USB powered. The
top photo shows a brief transient load that turns off the
charger but does not dip the V
voltage. The bottom
MAX
photo shows a prolonged transient condition that turns off
the charger and completely dips the V
voltage to the
MAX
point where the battery must provide current. For both
cases, normal operation resumes as soon as the transient
passes.
Extra capacitance can be connected to the V
pin to act
MAX
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, however, it may be desirable to use a larger capacitor connected to V
500mA/DIV
500mA/DIV
500mA/DIV
500mA/DIV
500mA/DIV
500mA/DIV
Figure 1. Handling Load Transients when USB Powered
to act as a larger reservoir. Up to 50µF of
MAX
V
MAX
2V/DIV
I
MAX
I
USB
I
BAT
100µs/DIV
USB Maximum Current Condition
V
MAX
2V/DIV
I
MAX
I
USB
I
BAT
100µs/DIV
USB Heavy Over-Current Condition
3455 F01a
3455 F01b
12
3455f
LTC3455
U
WUU
APPLICATIO S I FOR ATIO
ceramic capacitance may be connected to the V
without difficulty. More than 50µ F requires using a capacitor with some ESR 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.
Using the V
The V
MAX
Pin to Power Other Devices
MAX
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 V
will always draw power from the best available
MAX
input power source.
The internal PMOS connecting V
to the battery is
MAX
current limited to 900mA at startup (to minimize in-rush
current) and to 4A once V
has risen close to the battery
MAX
voltage. Because of the reduced startup current limit, the
turn-on of other devices powered from V
MAX
always be delayed to minimize the currrent initially needed
from the V
pin. The best choice is to enable these
MAX
devices from either switcher output, since the turn-on of
both switchers is always delayed until the V
reached the V
pin voltage. The V
BAT
MAX
MAX
pin is discharged
to ground when the LTC3455 is shut down, so that any
device supplied by V
will have its input grounded
MAX
during shutdown. This ensures output disconnect for all
supply voltages within the system.
pin
MAX
should
pin has
Startup and Shutdown when Battery-Powered
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.
When the momentary-on switch is first pressed, shorting
the ON pin to ground, PBSTAT goes low and the LTC3455
first brings up the V
pin, then enables Switcher 1 to
MAX
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 microcontroller that the push-button has been pressed. The
microcontroller prepares for shutdown then pulls the
PWRON signal low. When the push-button is released, 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 V
pin has reached the V
MAX
BAT
pin voltage.
PBSTAT
23
ON
24
PUSH
µC
BUTTON
PWRON
22
ON2
19
Figure 2. Momentary Push-Button Operation
LTC3455
SWITCHER 1
ENABLED
SWITCHER 2
ENABLED
3455 F02
3455f
13
LTC3455
U
WUU
APPLICATIO S I FOR ATIO
19
ON2
23
PBSTAT
24
ON
22
PWRON
9
V
BAT
WALLFB
USB
SUSPEND
+
3V
–
11
+
1.23V
–
8
+
3.9V
–
6
Figure 3. Turn-On Logic Diagram for LTC3455
LTC3455
SWITCHER 2
ENABLED
SWITCHER 1
ENABLED
CHARGER
ENABLED
USB POWER
CONTROLLER
ENABLED
3455 F03
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. 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
alive when external power is available (this is important for
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.
Starting Switcher 2/Power Supply Sequencing
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
V
pin. This will enable Switcher 2 after the output of
MAX
Switcher 1 has reached 90% of its final value. This powerup delay ensures proper supply sequencing and reduces
the peak battery current at startup. Figure 4 shows the
output sequencing when both switchers are enabled at
startup with the ON2 pin tied to V
switchers is always delayed until the V
the V
pin voltage.
BAT
. The turn-on of both
MAX
pin has reached
MAX
Reset Signal (RST)
A 200ms reset signal (the RST pin is pulled low) is
provided for proper initialization of a microcontroller whenever 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.
PWRON/ON2
2V/DIV
V
MAX
2V/DIV
V
(1.8V)
OUT1
2V/DIV
V
(3.3V)
OUT2
2V/DIV
100µs/DIV
Figure 4. Sequencing for Switcher 1 and 2 Outputs
3455 F04
14
3455f
LTC3455
U
WUU
APPLICATIO S I FOR ATIO
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 V
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 V
that Switcher 2 is also turned on at startup, then both
outputs must reach 90% of their final values within 200ms.
Once the output(s) are in regulation, the timer is reset for
a full 200ms.
Schottky Diode Selection/WALLFB Resistor Selection
pin will remain on as long as ON
MAX
MAX
so
Three good diode choices are the MBRM110E (1A, 10V),
MBR120ESF (1A, 20V), and the MBRA210E (2A, 10V). All
are available in very small packages from ON Semiconductor (www.onsemi.com), have reverse leakage currents
under 1µ A at room temperature, and have forward drops
of around 500mV at their maximum rated current
(1A or 2A).
V
10
V
MAX
LTC3455
WALLFB
Figure 5. Schottky Leakage Current Path
11
I
LEAKAGE
MAX
WALL 5V
3.32K
1.24K
3455 F05
Switching Regulator General Information
When a 5V wall adapter is used, power is provided to the
V
pin through a Schottky diode. The most important
MAX
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
leakage current should be minimized (by picking an appropriate 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 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 100µ A 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
be checked thoroughly to avoid problems due to excessive
diode leakage current.
The LTC3455 contains two 1.5MHz constant-frequency
current mode switching regulators that operate with efficiencies up to 96%. Switcher 1 provides up to 400mA at
1.5V/1.8V (to power a microcontroller core), and Switcher
2 provides up to 600mA at 3V/3.3V (to power microcontroller I/O, memory and other logic circuitry). Both converters 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.
3455f
15
LTC3455
U
WUU
APPLICATIO S I FOR ATIO
Switching Regulator Inductor 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. Keep
in mind that most inductors that are very thin or have a very
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
times larger than the maximum load current to ensure that
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
current rating, DCR and physical size. Consult each manufacturer for detailed information on their entire selection of
inductors.
Switching Regulator Output Capacitor Selection
Low ESR (equivalent series resistance) ceramic capacitors 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 10µ F
output capacitor is sufficient for most applications. Table
2 shows a list of several ceramic capacitor manufacturers.
Consult each manufacturer for detailed information on
their entire selection of ceramic capacitors. Many manufacturers now offer very thin (<1mm tall) ceramic capacitors ideal for use in height-restricted designs.
Table 2. Recommended Ceramic Capacitor Manufacturers
Taiyo Yuden (408) 573-4150 www.t-yuden.com
AVX (803) 448-9411 www.avxcorp.com
Murata (714) 852-2001 www.murata.com
TDK (888) 835-6646 www.tdk.com
Table 1. Recommended Inductors
Max Max
Inductor L I
Type (µH) (A) (Ω) (mm) Manufacturer
DB318C 4.7 0.86 0.1 1.8 Toko
10 0.58 0.18 1.8 (847)297-0070
CLS4D09 4.7 0.75 0.19 1 Sumida
10 0.5 0.37 1 (847)956-0666
CDRH3D16 4.7 0.9 0.11 1.8 Sumida
10 0.55 0.21 1.8
SD12 4.7 1.29 0.12 1.2 Cooper
10 0.82 0.28 1.2 (561)752-5000
ELT5KT 4.7 1 0.2 1.2 Panasonic
10 0.68 0.36 1.2 (408)945-5660
DC
DCR Height
www.toko.com
www.sumida.com
www.cooperet.com
www.panasonic.com
V
Pin Capacitor Selection
BAT
For the V
pin, a 4.7µ F to 10µF ceramic capacitor is the
BAT
best choice. Only X5R or X7R ceramic capacitors should
be used.
V
Pin Capacitor Selection
MAX
For the V
pin, a 10µF ceramic capacitor is the best
MAX
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 V
to act as a reservoir when the LTC3455
MAX
is USB powered. Up to 50µ F of ceramic capacitance may
be connected to the V
pin without difficulty. More than
MAX
50µ F 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.
16
3455f
LTC3455
U
WUU
APPLICATIO S I FOR ATIO
USB Pin and Wall Adapter Capacitor Selection
Caution must be exercised when using ceramic capacitors
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. Refer to Linear Technology Application Note 88,
entitled “Ceramic Input Capacitors Can Cause Overvoltage
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
if this ringing is not large enough to damage the part, it can
couple to the V
outputs) and be mistaken as loop instability. To bypass the
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, thus reducing the voltage ringing. Use 4.7µ F to 10µ F for
the USB pin, and 1µF or larger for the wall adapter input.
pin (and to the switching regulator
MAX
Burst Mode™ Operation
For highest efficiencies at light loads, both DC/DC converters are capable of operating in Burst Mode. In this mode,
energy is delivered to the outputs in shorts bursts, which
minimizes switching losses and quiescent-current losses.
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
70
Burst
Mode
60
50
EFFICIENCY (%)
40
30
20
Figure 7. PWM and Burst Mode Efficiency
1.8V
PWM Mode
1
3.3V
PWM Mode
V
= 3.6V
BAT
10 100 1000
LOAD CURRENT (mA)
3455 F07
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):
R
2
VV
=+
08 1
OUT
.•
R
1
Typical values for R1 are in the range of 80k to 400k.
V
OUT
R2
R1
3455 F06
GND
1, 18
25
FB1, FB2
LTC3455
Figure 6. Setting the Output Voltage
Tie the MODE pin to V
to always allow automatic Burst
MAX
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
operation might be undesirable at certain times (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
the most. Burst Mode is disabled initially at startup (for the
first 200ms) and also whenever external power is available, even if the MODE pin is pulled high.
Figure 8 shows the switching waveforms for switcher 1
(both PWM mode and Burst Mode Operation) with VIN =
3.6V, V
Burst Mode is a registered trademark of Linear Technology Corporation.
= 1.8V, and I
OUT1
OUT1
= 25mA.
3455f
17
LTC3455
U
WUU
APPLICATIO S I FOR ATIO
Burst Mode
V
SW1
2V/DIV
V
OUT1
50mV/DIV
AC COUPLED
I
L1
100mA/DIV
V
SW1
2V/DIV
V
OUT1
10mV/DIV
AC COUPLED
I
L1
100mA/DIV
Figure 8. Burst Mode and PWM Mode Waveforms
5µs/DIV
PWM Mode
1µs/DIV
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. Figure 9 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).
3455 F08a
3455 F08b
In-Rush Current Limiting
When the LTC3455 is battery-powered, an internal 0.15Ω
PMOS switch connects the battery (V
pin) to the V
BAT
MAX
pin to provide power for both switchers and other internal
circuitry. This PMOS switch is turned off in shutdown, and
the V
pin discharges to ground, providing output
MAX
disconnect for all outputs. At startup, this PMOS must first
charge up any capacitance present on the V
pin to the
MAX
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 V
voltage is ramping up. Once V
reaches the battery
MAX
MAX
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 wellcontrolled while V
is ramping up and while both
MAX
switchers outputs are rising.
Battery Charger General Information
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 immediately when external power is applied. For such applications, an NMOS switch can be used to disconnect the
R
resistor and allow the PROG pin to float high,
PROG
turning off the charger. In this manner, charging occurs
only when allowed by the microcontroller.
V
OUT1
V
OUT2
500mA/DIV
18
V
MAX
2V/DIV
(1.8V)
2V/DIV
(3.3V)
2V/DIV
I
BAT
100µs/DIV
Figure 9. In-Rush Current at Startup
3455 F09
The LTC3455 battery charger is a constant-current, constant-voltage charger. In constant-current mode, the maximum charge current is set by a single external resistor.
When the battery approaches the final float voltage, the
charge current begins to decrease as the charger switches
to constant-voltage mode. The charge cycle is terminated
only by the charge timer.
3455f
LTC3455
U
WUU
APPLICATIO S I FOR ATIO
Charge and Recharge Cycles
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
continue until the battery voltage exceeds the 4.05V threshold. 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.
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 temporarily, or the SUSPEND pin is temporarily pulled high (if the
LTC3455 is under USB power).
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):
Capacitance on the PROG pin should be minimized to
ensure loop stability when in constant-current mode. Do
not place a capacitor directly from the PROG pin to ground.
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 significantly with normal load transients.
LTC3455
PROG
10k
C
FILTER
2
PROG
GND
25
Figure 10. Monitoring Average Charge Current
R
CHARGE
CURRENT
MONITOR
CIRCUITRY
3455 F10
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:
T
(hours) = C
TIMER
• (3 hours) / (0.1µF)
TIMER
Trickle Charge and Defective Battery Detection
R
= 1000 • 1.23V / I
PROG
BAT
If only USB power is used (no wall adapter), select the
R
value to be 2.49kΩ (or larger) to set the maximum
PROG
charge current at 500mA. If a wall adapter is also used,
I
CHARGE
R
can be programmed up to 1A (with a 1.24kΩ
value), and the USB power manager will automati-
PROG
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.
I
= 1000 • 1.23V / R
BAT
PROG
If the battery voltage is below 2.85V at the beginning of the
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
SUSPEND pin is temporarily pulled high (if the LTC3455 is
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.
3455f
19
LTC3455
V
USB
(V)
3.75
0
CHARGE CURRENT (mA)
100
200
300
400
500
4.00
4.25 4.50 4.75
3455 F12
5.00 5.25
I
BAT
USB HIGH POWER MODE
V
BAT
= 3.6V
U
WUU
APPLICATIO S I FOR ATIO
Battery Charger Thermal Limit
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 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. 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 automatically reduce the current under worst-case conditions.
CHRG Status Output
The CHRG 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.
This NMOS device is capable of driving an external LED.
This pin does not provide any C/10 information.
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.
Figure 12. Charge Current vs USB Voltage
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
total system current under the strict 500mA/100mA USB
limit. The graph in Figure 11 shows how charge current,
I
, decreases as the current needed for the rest of the
BAT
system increases (both switchers and all other external
devices pull current from the V
current, I
pin). The total USB
MAX
, always stays below 500mA.
USB
500
I
400
300
200
100
CHARGE AND USB CURRENT (mA)
–100
Figure 11. Charge Current vs Total System Current
0
USB HIGH POWER MODE
= 5V
V
USB
= 3.6V
V
BAT
0
100
TOTAL SYSTEM CURRENT (mA)
USB
I
BAT
200 300 400
500 600
3455 F11
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).
Constant-Current-Only Charger/Disabling the
Charger␣ Timer
To use the charger in a constant-current-only mode,
connect the TIMER pin to V
to disable the timer,
MAX
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 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. Disabling the voltage amplifier allows the
super-cap/backup battery to charge up fully to the available USB or wall adapter voltage.
3455f
20
LTC3455
1.8V
LBO
17
1M
LOW-BATTERY
DECTECTOR
V
BAT
16
2.49M
806k
3.3V
17
100k
3455 F14
LDO
2.5V
16
169k
100pF
80.6k
AO
LTC3455
AI
AO
LTC3455
AI
10µF
U
WUU
APPLICATIO S I FOR ATIO
Hot Swap Output
A current limited Hot Swap output is provided for powering 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.
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
shown in Figure 13. The LDO is convenient for applications
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.
The gain block is alive whenever switcher 1 is enabled, 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
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 intelligence in the system.
PCB Layout Considerations
As with all DC/DC converters, careful attention must be
paid to the printed circuit board (PCB) layout and component placement. The V
capacitor, V
BAT
capacitor, and
MAX
both inductors must all be placed as close as possible to
the LTC3455. These components, along with both DC/DC
converter output capacitors, should be placed on the same
side of the circuit board as the LTC3455, with their
connections made on that top layer. Place a local, unbroken ground plane below these components that is tied to
the exposed pad of the LTC3455. The exposed pad (pin 25)
must be soldered to the PCB (to system ground) for proper
operation.
U
TYPICAL APPLICATIO S
Standalone USB Power Supply
with Temporary Backup Power
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. The battery charger can then be used to charge up
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
follow proper shutdown procedures when the main power
source is abruptly removed. Figure 14 shows a standalone
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 V
pin voltage drops to
MAX
4V, notifying the microcontroller of an impending dropout
condition. The 1MΩ resistor connected between the AI
3455f
21
LTC3455
TYPICAL APPLICATIO S
U
USB 5V
4.7µF
1Ω
C6
1.8V
DROPOUT
V
MAX
USB
CONTROLLER
C5
10µF
V
C4
4700µF
10k
82.5k
20k
8
USB
6
SUSPEND
5
USBHP
10
V
MAX
LTC3455
4
CHRG
11
WALLFB
3
MAX
TIMER
2
PROG
2.49k
9
V
BAT
17
AO
1M
16
AI
C1, C2, C3, C5, C6: X5R OR X7R CERAMIC
L1, L2: TOKO DB318C
ALL RESISTORS 1%
MODE
HSON
ON2
PWRON
RST
PBSTAT
HSO
HSI
SW2
FB2
SW1
FB1
GND
3455 TA02
21
15
19
22
20
23
24
ON
14
13
12
18
7
1
25
Figure 14. Standalone USB Power Supply with
Temporary Backup Power
1M
L2, 4.7µH
10pF
L1, 4.7µH
10pF
1M
ON/OFF
µC
1.8V
3.3V, HS
C3
1µF
249k
80.6k
100k
80.6k
3.3V
0.4A
C2
10µF
1.8V
0.2A
C1
10µF
USB 5V
1Ω
C6
4.7µF
WALL 5V
1Ω
C7
1µF
SINGLE
CELL Li-ION
3.3V TO 4.2V
C1 TO C8: X5R OR X7R CERAMIC
L1, L2: TOKO DB318C
D1: ON SEMI MBRM110E
ALL RESISTORS 1%
USB
CONTROLLER
C5
D1
10µF
3.32k
1.24k
+
C8, 0.1µF
C4
4.7µF
1k
2.49k
10
11
8
6
5
4
3
2
9
USB
SUSPEND
USBHP
V
MAX
CHRG
WALLFB
TIMER
PROG
V
BAT
LTC3455
MODE
HSON
ON2
PWRON
RST
PBSTAT
HSO
HSI
SW2
FB2
SW1
FB1
GND
ON
AO
AI
3455 F15
21
15
19
22
20
23
24
14
17
13
12
16
18
7
1
25
1M
C3
1µF
L2, 4.7µH
100pF
L1, 4.7µH
10pF
1M
3.3V, HS
1k
Figure 15. LTC3455 Application with 3.3V Output Current
Increased to 1.2A
ON/OFF
µC
249k
2.49k
80.6k
100k
80.6k
1.8V
M1
FDN304P
OR
Si2305DS
V
MAX
3.3V
1.2A
C2
2x10µF
1.8V
0.4A
C1
10µF
and AO pins provides 150mV of hysteresis (the dropout
indicator stays low until the V
4.15V). A 4700µ F backup capacitor connected to the V
pin rises back above
MAX
BAT
pin briefly provides power to the system after the USB
supply has been removed, and also helps support transient loads that slightly exceed the USB current limit.
Connecting this large capacitance to the V
pin has
BAT
several advantages. It provides a large energy reservoir
that is isolated from both the USB pin (the USB specification limits capacitance on the USB supply pin to 10µF or
less) and the V
pin (using a very large capacitance on
MAX
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 V
, the battery charger operates
MAX
in constant-current mode (the voltage-loop and timer
function are disabled), so the 4700µ F 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 typically provides a 3.3V, 600mA output. While this output
current is sufficient for many portable devices, some
applications need a 3.3V supply capable of providing more
than 1A. Figure 15 shows how to implement a higher
current 3.3V output using the LTC3455. By adding one tiny
SOT23 PMOS and using the AI/AO amplifier as an LDO, the
3.3V output now provides 1.2A of output current. 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
normally provide all of the output current, and the LDO will
turn on briefly to provide the higher load currents.
22
3455f
U
TYPICAL APPLICATIO S
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.
U
PACKAGE DESCRIPTIO
UF Package
24-Lead Plastic QFN (4mm × 4mm)
(Reference LTC DWG # 05-08-1697)
LTC3455
V
(3.3V)
OUT2
100mV/DIV
AC COUPLED
I
OUT2
0.5A/DIV
0.5A TO 1.2A STEP
M1 GATE
2V/DIV
500µs/DIV
Figure 16. Load Current Step (0.5A to 1.2A) for 3.3V Output
3455 F16
4.50 ± 0.05
3.10 ± 0.05
2.45 ± 0.05
(4 SIDES)
RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS
4.00 ± 0.10
(4 SIDES)
PIN 1
TOP MARK
(NOTE 6)
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
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 representation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
0.70 ±0.05
0.25 ±0.05
0.50 BSC
PACKAGE OUTLINE
0.75 ± 0.05
2.45 ± 0.10
(4-SIDES)
0.200 REF
0.00 – 0.05
BOTTOM VIEW—EXPOSED PAD
R = 0.115
TYP
0.23 TYP
(4 SIDES)
24
23
0.38 ± 0.10
1
2
(UF24) QFN 1103
0.25 ± 0.05
0.50 BSC
3455f
23
LTC3455
TYPICAL APPLICATIO
U
USB 5V
1Ω
C6
4.7µF
WALL 5V
1Ω
C7
1µF
REMOVE THESE
COMPONENTS IF
WALL ADAPTER
IS NOT USED
SINGLE
CELL Li-ION
3.3V TO 4.2V
USB
CONTROLLER
D1
3.32k
1.24k
+
1.8V
V
10µF
LBO
BAT
2.49M
806k
C5
C8, 0.1µF
4.7µF
C4
1M
8
USB
6
SUSPEND
5
USBHP
10
V
MAX
1k
4
CHRG
11
WALLFB
3
TIMER
2
2.49k
PROG
9
V
BAT
17
AO
16
AI
C1 TO C8: X5R OR X7R CERAMIC
L1, L2: TOKO DB318C
D1: ON SEMI MBRM110E
ALL RESISTORS 1%
LTC3455
MODE
HSON
ON2
PWRON
RST
PBSTAT
ON
HSO
HSI
SW2
FB2
SW1
FB1
GND
3455 TA03
21
15
19
22
20
23
24
14
13
12
18
7
1
25
1M
L2, 4.7µH
10pF
L1, 4.7µH
10pF
1M
ON/OFF
µC
C3
1µF
1.8V
3.3V, HS
249k
80.6k
100k
80.6k
3.3V
0.5A
C2
10µF
1.8V
0.4A
C1
10µF
RELATED PARTS
PART NUMBER DESCRIPTION COMMENTS
LT1616 500mA (I
DC/DC Converter I
LTC1879 1.2A (I
DC/DC Converter I
LTC3405/LTC3405A 300mA (I
DC/DC Converter I
LTC3406/LTC3406B 600mA (I
DC/DC Converter I
LTC3407 Dual 600mA (I
DC/DC Converter I
LTC3412 2.5A (I
DC/DC Converter I
LTC3414 4A (I
DC/DC Converter I
LTC3440/LTC3441 600mA/1A (I
DC/DC Converter I
Linear Technology Corporation
24
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900 ● FAX: (408) 434-0507
), 1.4MHz, High Efficiency Step-Down 90% Efficiency, VIN: 3.6V to 25V, V
OUT
), 550kHz, Synchronous Step-Down 95% Efficiency, VIN: 2.7V to 10V, V
OUT
), 1.5MHz, Synchronous Step-Down 95% Efficiency, VIN: 2.7V to 6V, V
OUT
), 1.5MHz, Synchronous Step-Down 96% Efficiency, VIN: 2.5V to 5.5V, V
OUT
), 1.5MHz, Synchronous Step-Down 96% Efficiency, VIN: 2.5V to 5.5V, V
OUT
), 4MHz, Synchronous Step-Down 95% Efficiency, VIN: 2.5V to 5.5V, V
OUT
), 4MHz, Synchronous Step-Down 95% Efficiency, VIN: 2.25V to 5.5V, V
OUT
), 2MHz/1MHz, Synchronous Buck-Boost 95% Efficiency, VIN: 2.5V to 5.5V, V
OUT
●
www.linear.com
<1µA, ThinSOT
SD
<1µA, TSSOP16
SD
<1µA, ThinSOT
SD
<1µA, ThinSOT
SD
<1µA, MS10E
SD
<1µA, TSSOP16E
SD
<1µA, TSSOP16E
SD
<1µA, MS/DFN
SD
= 1.25V, IQ = 1.9mA,
OUT(MIN)
= 0.8V, IQ = 15µA,
OUT(MIN)
= 0.8V, IQ = 20µA,
OUT(MIN)
= 0.6V, IQ = 20µA,
OUT(MIN)
= 0.6V, IQ = 40µA,
OUT(MIN)
= 0.8V, IQ = 60µA,
OUT(MIN)
= 0.8V, IQ = 64µA,
OUT(MIN)
= 2.5V, IQ = 25µA/50µA,
OUT(MIN)
3455f
LT/TP 0304 1K • PRINTED IN USA
LINEAR TECHNOLOGY CORPORATION 2004
Loading...