LTC3400/LTC3400B
1
3400f
s
Pagers
s
MP3 Players
s
Digital Cameras
s
LCD Bias Supplies
s
Handheld Instruments
s
Wireless Handsets
s
GPS Receivers
s
Up to 92% Efficiency
s
Generates 3.3V at 100mA from a Single AA Cell
s
Low Start-Up Voltage: 0.85V
s
1.2MHz Fixed Frequency Switching
s
Internal Synchronous Rectifier
s
2.5V to 5V Output Range
s
Automatic Burst Mode
Operation (LTC3400)
s
Continuous Switching at Light Loads (LTC3400B)
s
Logic Controlled Shutdown (< 1
A)
s
Antiringing Control Minimizes EMI
s
Tiny External Components
s
Low Profile (1mm) ThinSOT
TM
Package
600mA, 1.2MHz Micropower
Synchronous Boost Converter
in ThinSOT
Figure 1. Single Cell to 3.3V Synchronous Boost Converter
The LTC
3400/LTC3400B are synchronous, fixed fre-
quency, step-up DC/DC converters delivering high effi-
ciency in a 6-lead ThinSOT package. Capable of supplying
3.3V at 100mA from a single AA cell input, the devices
contain an internal NMOS switch and PMOS synchronous
rectifier.
A switching frequency of 1.2MHz minimizes solution
footprint by allowing the use of tiny, low profile inductors
and ceramic capacitors. The current mode PWM design is
internally compensated, reducing external parts count.
The LTC3400 features automatic shifting to power saving
Burst Mode operation at light loads, while the LTC3400B
features continuous switching at light loads. Antiringing
control circuitry reduces EMI concerns by damping the
inductor in discontinuous mode, and the devices feature
low shutdown current of under 1
A.
Both devices are available in the low profile (1mm) ThinSOT
package.
ThinSOT is a trademark of Linear Technology Corporation.
SW
L1
4.7
H
V
OUT
LTC3400
FB
V
IN
SHDN
2
1
3
3400 F01
R1
1.02M
1%
C1, C2: TAIYO-YUDEN X5R EMK316BJ475ML
L1: COILCRAFT DO160C-472
R2
604k
1%
C2
4.7
F
C1
4.7
F
SINGLE
AA CELL
V
OUT
3.3V
100mA
5
4
6
GND
+
OFF ON
LOAD CURRENT (mA)
60
EFFICIENCY (%)
80
100
50
70
90
0.1
10
100
1000
3400 F01a
40
1
V
IN
= 2.4V
V
IN
= 1.5V
FIGURE 1 CIRCUIT
WITH OPTIONAL SCHOTTKY DIODE
(SEE APPLICATIONS INFORMATION)
Efficiency
FEATURES
DESCRIPTIO
U
APPLICATIO S
U
TYPICAL APPLICATIO
U
, LTC, LT and Burst Mode are registered trademarks of Linear Technology Corporation.
LTC3400/LTC3400B
2
3400f
V
IN
Voltage ................................................. 0.3V to 6V
SW Voltage ................................................. 0.3V to 6V
SHDN, FB Voltage ....................................... 0.3V to 6V
V
OUT
........................................................... 0.3V to 6V
Operating Temperature Range (Note 2) .. 30
C to 85
C
Storage Temperature Range ................... 65
C to 125
Lead Temperature (Soldering, 10 sec).................. 300
C
ORDER PART
NUMBER
S6 PART MARKING
T
JMAX
= 125
C,
JA
= 256
C/W
LTWK
LTUN
LTC3400ES6
LTC3400BES6
(Note 1)
Note 1: Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired.
Note 2: The LTC3400E/LTC3400BE are guaranteed to meet performance
specifications from 0
C to 70
C. Specifications over the 30
C to 85
C
operating temperature range are assured by design, characterization and
correlation with statistical process controls.
The
q
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25
C. V
IN
= 1.2V, V
OUT
= 3.3V, unless otherwise specified.
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
Minimum Start-Up Voltage
I
LOAD
= 1mA
0.85
1
V
Minimum Operating Voltage
SHDN = V
IN
(Note 4)
0.5
0.65
V
Output Voltage Adjust Range
2.5
5
V
Feedback Voltage
q
1.192
1.23
1.268
V
Feedback Input Current
V
FB
= 1.25V (Note 3)
1
nA
Quiescent Current (Burst Mode Operation)
V
FB
= 1.4V (Note 5), LTC3400 Only
19
30
A
Quiescent Current (Shutdown)
V
SHDN
= 0V, Not Including Switch Leakage
0.01
1
A
Quiescent Current (Active)
Measured On V
OUT
300
500
A
NMOS Switch Leakage
V
SW
= 5V
0.1
5
A
PMOS Switch Leakage
V
SW
= 0V
0.1
5
A
NMOS Switch On Resistance
V
OUT
= 3.3V
0.35
V
OUT
= 5V
0.20
PMOS Switch On Resistance
V
OUT
= 3.3V
0.45
V
OUT
= 5V
0.30
NMOS Current Limit
600
850
mA
Burst Mode Operation Current Threshold
LTC3400 Only (Note 3)
3
mA
Current Limit Delay to Output
(Note 3)
40
ns
Max Duty Cycle
V
FB
= 1.15V
q
80
87
%
Switching Frequency
0.95
1.2
1.5
MHz
q
0.85
1.2
1.5
MHz
SHDN Input High
1
V
SHDN Input Low
0.35
V
SHDN Input Current
V
SHDN
= 5.5V
0.01
1
A
ABSOLUTE AXI U RATI GS
W
W
W
U
PACKAGE/ORDER I FOR ATIO
U
U
W
ELECTRICAL CHARACTERISTICS
Note 3: Specification is guaranteed by design and not 100% tested in
production.
Note 4: Minimum V
IN
operation after start-up is only limited by the
battery's ability to provide the necessary power as it enters a deeply
discharged state.
Note 5: Burst Mode operation I
Q
is measured at V
OUT
. Multiply this value
by V
OUT
/V
IN
to get the equivalent input (battery) current.
SW 1
GND 2
FB 3
6 V
IN
5 V
OUT
4 SHDN
TOP VIEW
S6 PACKAGE
6-LEAD PLASTIC SOT-23
Consult LTC Marketing for parts specified with wider operating temperature ranges.
LTC3400/LTC3400B
3
3400f
TYPICAL PERFOR A CE CHARACTERISTICS
U
W
Output Load Burst Mode Threshold
vs V
IN
V
IN
(V)
0.9
0
OUTPUT CURRENT (mA)
1.5
2.1
2.7
3.3
3400 G01
3.9
4.5
20
10
V
OUT
= 3.3V
V
OUT
= 5V
L = 4.7
H
T
A
= 25
C
TEMPERATURE (
C)
60
3.24
V
OUT
(V)
3.26
3.28
3.30
3.32
3.36
30
0
30
60
3400 G02
90
120
3.34
FIGURE 1 CIRCUIT
I
O
= 10mA
I
OUT
(mA) CURRENT SOURCE LOAD
0.1
0.8
START-UP VOLTAGE (V)
1.2
1.3
1.4
1
10
100
3400 G03
1.1
1.0
0.9
T
A
= 25
C
V
OUT
vs Temperature
Minimum Start-Up Voltage
vs Load Current
No Load Battery Current vs V
BATT
BATTERY VOLTAGE (V)
1.2
10
100
1000
1.8
3400 G04
BATTERY CURRENT (
A)
0.9
3.0
1.5
2.1
2.4
2.7
V
OUT
= 3.3V
T
A
= 25
C
SW Pin Fixed Frequency,
Continuous Inductor Current
Operation
TEMPERATURE (
C)
50
NORMALIZED FREQUENCY
0.99
1.00
1.01
10
50
3400 G05
0.98
0.97
30
10
30
70
90
0.96
0.95
SW Pin Antiringing Operation
Fixed Frequency and Burst Mode
Operation
V
OUT
Transient Response
Normalized Oscillator Frequency
vs Temperature
V
SW
1V/DIV
0V
V
IN
= 1.3V
100ns/DIV
3400 G06
V
OUT
= 3.3V
I
OUT
= 10mA
L = 6.8
H
C
OUT
= 4.7
F
V
SW
1V/DIV
0V
V
IN
= 1.3V
100ns/DIV
3400 G07
V
OUT
= 3.3V
I
OUT
= 50mA
L = 6.8
H
C
OUT
= 4.7
F
V
OUT(AC)
100mV/DIV
60mA
V
IN
= 1.3V
10ms/DIV
3400 G08
V
OUT
= 3.3V
I
OUT
= 60mA TO 10
A
L = 6.8
H
C
OUT
= 4.7
F
10
A
I
OUT
V
OUT(AC)
100mV/DIV
100mA
V
IN
= 1.3V
100
s/DIV
3400 G09
V
OUT
= 3.3V
I
OUT
= 40mA TO 100mA
L = 6.8
H
C
OUT
= 4.7
F
40mA
I
OUT
LTC3400/LTC3400B
4
3400f
U
U
U
PI FU CTIO S
SW (Pin 1): Switch Pin. Connect inductor between SW
and V
IN
. Optional Schottky diode is connected between
SW and V
OUT
. Keep these PCB trace lengths as short and
wide as possible to reduce EMI and voltage overshoot. If
the inductor current falls to zero, or SHDN is low, an
internal 100
antiringing switch is connected from SW to
V
IN
to minimize EMI.
GND (Pin 2): Signal and Power Ground. Provide a short
direct PCB path between GND and the () side of the output
capacitor(s).
FB (Pin 3): Feedback Input to the
g
m
Error Amplifier.
Connect resistor divider tap to this pin. The output voltage
can be adjusted from 2.5V to 5V by:
V
OUT
= 1.23V [1 + (R1/R2)]
SHDN (Pin 4): Logic Controlled Shutdown Input.
SHDN = High: Normal free running operation, 1.2MHz
typical operating frequency.
SHDN = Low: Shutdown, quiescent current < 1
A.
100
connected between SW and V
IN
.
Typically, SHDN should be connected to V
IN
through a 1M
pull-up resistor.
V
OUT
(Pin 5): Output Voltage Sense Input and Drain of the
Internal Synchronous Rectifier MOSFET. Bias is derived
from V
OUT
. PCB trace length from V
OUT
to the output filter
capacitor(s) should be as short and wide as possible. V
OUT
is held at V
IN
0.6V in shutdown due to the body diode of
the internal PMOS.
V
IN
(Pin 6): Battery Input Voltage. The device gets its
start-up bias from V
IN
. Once V
OUT
exceeds V
IN
, bias
comes from V
OUT
. Thus, once started, operation is com-
pletely independent from V
IN
. Operation is only limited by
the output power level and the battery's internal series
resistance.
1.23V
REF
Burst Mode
OPERATION
CONTROL
SHUTDOWN
CONTROL
SLOPE
COMP
PWM
CONTROL
START-UP
OSC
MUX
A
B
A/B
RAMP
GEN
1.2MHz
FB
3400 BD
3
V
OUT
OPTIONAL
SCHOTTKY
L1
4.7
H
5
SW
1
V
IN
SINGLE
CELL
INPUT
6
SHDN
4
GND
2
+
g
m
ERROR
AMP
+
V
OUT
GOOD
+
PWM
COMPARATOR
R
C
80k
SHUTDOWN
C
C
150pF
C
P2
2.5pF
R2
604k
1%
(EXTERNAL)
R1
1.02M
1%
(EXTERNAL)
SLEEP
SYNC
DRIVE
CONTROL
0.35
0.45
2.3V
C
OUT
4.7
F
3.3V
OUTPUT
C
IN
1
F
+
CURRENT
SENSE
BLOCK DIAGRA
W
LTC3400/LTC3400B
5
3400f
OPERATIO
U
The LTC3400/LTC3400B are 1.2MHz, synchronous boost
converters housed in a 6-lead ThinSOT package. Able to
operate from an input voltage below 1V, the devices
feature fixed frequency, current mode PWM control for
exceptional line and load regulation. With its low R
DS(ON)
and gate charge internal MOSFET switches, the devices
maintain high efficiency over a wide range of load current.
Detailed descriptions of the three distinct operating modes
follow. Operation can be best understood by referring to
the Block Diagram.
Low Voltage Start-Up
The LTC3400/LTC3400B will start up at a typical V
IN
volt-
age of 0.85V or higher. The low voltage start-up circuitry
controls the internal NMOS switch up to a maximum peak
inductor current of 850mA (typ), with an approximate
1.5
s off-time during start-up, allowing the devices to
start up into an output load. Once V
OUT
exceeds 2.3V, the
start-up circuitry is disabled and normal fixed frequency
PWM operation is initiated. In this mode, the LTC3400/
LTC3400B operate independent of V
IN
, allowing extended
operating time as the battery can droop to several tenths
of a volt without affecting output voltage regulation. The
limiting factor for the application becomes the ability of the
battery to supply sufficient energy to the output.
Low Noise Fixed Frequency Operation
Oscillator: The frequency of operation is internally set to
1.2MHz.
Error Amp: The error amplifier is an internally compensated
transconductance type (current output) with a transconduc-
tance (g
m
) = 33 microsiemens. The internal 1.23V reference
voltage is compared to the voltage at the FB pin to generate
an error signal at the output of the error amplifier. A volt-
age divider from V
OUT
to ground programs the output
voltage via FB from 2.5V to 5V using the equation:
V
OUT
= 1.23V [1 + (R1/R2)]
Current Sensing: A signal representing NMOS switch
current is summed with the slope compensator. The
summed signal is compared to the error amplifier output
to provide a peak current control command for the PWM.
Peak switch current is limited to approximately 850mA
independent of input or output voltage. The current signal
is blanked for 40ns to enhance noise rejection.
Zero Current Comparator: The zero current comparator
monitors the inductor current to the output and shuts off
the synchronous rectifier once this current reduces to ap-
proximately 20mA. This prevents the inductor current from
reversing in polarity improving efficiency at light loads.
Antiringing Control: The antiringing control circuitry pre-
vents high frequency ringing of the SW pin as the inductor
current goes to zero by damping the resonant circuit
formed by L and C
SW
(capacitance on SW pin).
Burst Mode Operation
Portable devices frequently spend extended time in low
power or standby mode, only switching to high power
drain when specific functions are enabled. In order to
improve battery life in these types of products, high power
converter efficiency needs to be maintained over a wide
output power range. In addition to its high efficiency at
moderate and heavy loads, the LTC3400 includes auto-
matic Burst Mode operation that improves efficiency of
the power converter at light loads. Burst mode operation
is initiated if the output load current falls below an
internally programmed threshold (see Typical Perfor-
mance graph, Output Load Burst Mode Threshold vs V
IN
).
Once initiated, the Burst Mode operation circuitry shuts
down most of the device, only keeping alive the circuitry
required to monitor the output voltage. This is referred to
as the sleep state. In sleep, the LTC3400 draws only 19
A
from the output capacitor, greatly enhancing efficiency.
When the output voltage has drooped approximately 1%
from nominal, the LTC3400 wakes up and commences
normal PWM operation. The output capacitor recharges
and causes the LTC3400 to reenter sleep if the output load
remains less than the sleep threshold. The frequency of
this intermittent PWM or burst operation is proportional to
load current; that is, as the load current drops further
below the burst threshold, the LTC3400 turns on less
frequently. When the load current increases above the
burst threshold, the LTC3400 will resume continuous
PWM operation seamlessly. The LTC3400B does not use
Burst Mode operation and features continous operation at
light loads, eliminating low frequency output voltage ripple
at the expense of light load efficiency.
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