LTC3400-1
600mA, 1.2MHz Micropower
Synchronous Boost Converter
in ThinSOT
FEATURES
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DESCRIPTIO
Up to 92% Efficiency
Generates 3.3V at 100mA from a Single AA Cell
Low Start-Up Voltage: 0.85V
V
OUT
Connected to V
IN
in Shutdown
Internal Synchronous Rectifier
2.5V to 5V Output Range
Automatic Burst Mode
®
Operation
Logic Controlled Shutdown (< 1µA)
Antiringing Control Minimizes EMI
Tiny External Components
Low Profile (1mm) SOT-23 Package
The LTC
®
3400-1 is a synchronous, fixed frequency, step-
up DC/DC converter delivering high efficiency in a 6-lead
ThinSOT™ package. Capable of supplying 3.3V at 100mA
from a single AA cell input, the device contains 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 LTC3400-1 features automatic shifting to power sav-
ing Burst Mode operation at light loads. In shutdown, V
OUT
and V
IN
are connected, which allows the input battery to be
used for backup power. The LTC3400-1 features low
shutdown current of under 1µA.
The LTC3400-1 is offered in the low profile (1mm)
SOT-23 package.
, LTC, LT and Burst Mode are registered trademarks of Linear Technology Corporation.
ThinSOT is a trademark of Linear Technology Corporation.
US Patent Numbers 5,481,178; 6,580,258; 6,304,066; 6,127,815; 6,498,466; 6,611,131.
APPLICATIO S
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Pagers
MP3 Players
Digital Cameras
LCD Bias Supplies
Handheld Instruments
Wireless Handsets
GPS Receivers
TYPICAL APPLICATIO
100
Single Cell to 3.3V Synchronous Boost Converter
90
4.7µH
SINGLE
AA CELL
4.7µF
V
IN
EFFICIENCY (%)
+
80
70
60
50
SW
V
OUT
1.02M
1%
604k
1%
LTC3400-1
OFF ON
SHDN
GND
FB
V
OUT
3.3V
100mA
4.7µF
FIGURE 1 CIRCUIT
WITH OPTIONAL SCHOTTKY DIODE
(SEE APPLICATIONS INFORMATION)
1
10
100
LOAD CURRENT (mA)
1000
34001 F01a
34001 F01
40
0.1
U
Efficiency
V
IN
= 2.4V
V
IN
= 1.5V
34001f
U
U
1
LTC3400-1
ABSOLUTE
(Note 1)
AXI U
RATI GS
PACKAGE/ORDER I FOR ATIO
TOP VIEW
SW 1
GND 2
FB 3
6 V
IN
5 V
OUT
4 SHDN
V
IN
Voltage ................................................. – 0.3V to 6V
SW Voltage
DC .......................................................... – 0.3V to 6V
Pulsed (<100ns) ......................................– 0.3V to 7V
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
LTC3400ES6-1
S6 PART MARKING
LTBJM
S6 PACKAGE
6-LEAD PLASTIC TSOT-23
T
JMAX
= 125°C,
θ
JC
= 102°C/W
Consult LTC Marketing for parts specified with wider operating temperature ranges.
ELECTRICAL CHARACTERISTICS
PARAMETER
Minimum Start-Up Voltage
Minimum Operating Voltage
Output Voltage Adjust Range
Feedback Voltage
Feedback Input Current
Quiescent Current (Burst Mode Operation)
Quiescent Current (Shutdown)
Quiescent Current (Active)
NMOS Switch Leakage
PMOS Switch Leakage
NMOS Switch On Resistance
PMOS Switch On Resistance
NMOS Current Limit
Burst Mode Operation Current Threshold
Current Limit Delay to Output
Max Duty Cycle
Switching Frequency
(Note 3)
(Note 3)
The
●
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.
CONDITIONS
I
LOAD
= 1mA
SHDN = V
IN
(Note 4)
2.5
●
MIN
TYP
0.85
0.5
MAX
1
0.65
5
1.268
30
1
500
5
UNITS
V
V
V
V
nA
µA
µA
µA
µA
µA
Ω
Ω
Ω
Ω
mA
mA
ns
%
1.192
1.23
1
19
0.01
300
0.1
0.1
0.35
0.20
0.45
0.30
V
FB
= 1.25V (Note 3)
V
FB
= 1.4V (Note 5)
V
SHDN
= 0V, Not Including Switch Leakage, V
IN
= V
OUT
Measured On V
OUT
V
SW
= 5V
V
SW
= 0V (Note 3)
V
OUT
= 3.3V
V
OUT
= 5V
V
OUT
= 3.3V
V
OUT
= 5V
600
850
3
40
V
FB
= 1.15V
●
●
80
0.95
0.85
1
87
1.2
1.2
1.5
1.5
0.35
SHDN Input High
SHDN Input Low
SHDN Input Current
V
SHDN
= 5.5V
0.01
1
Note 1:
Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired.
Note 2:
The LTC3400-1 is 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.
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.
34001f
2
U
MHz
MHz
V
V
µA
W
U
U
W W
W
LTC3400-1
TYPICAL PERFOR A CE CHARACTERISTICS
Output Load Burst Mode Threshold
vs V
IN
L = 4.7µH
T
A
= 25°C
OUTPUT CURRENT (mA)
20
V
OUT
= 3.3V
V
OUT
= 5V
3.32
V
OUT
(V)
3.30
3.28
3.26
3.36
3.34
START-UP VOLTAGE (V)
10
0
0.9
1.5
2.1
2.7
V
IN
(V)
3.3
3.9
4.5
3400 G01
No Load Battery Current vs V
BATT
1000
V
OUT
= 3.3V
T
A
= 25°C
NORMALIZED FREQUENCY
BATTERY CURRENT (µA)
100
10
0.9
1.2
1.5 1.8 2.1 2.4
BATTERY VOLTAGE (V)
SW Pin Fixed Frequency,
Continuous Inductor Current
Operation
V
SW
1V/DIV
0V
V
IN
= 1.3V
V
OUT
= 3.3V
I
OUT
= 50mA
L = 6.8µH
C
OUT
= 4.7µF
100ns/DIV
3400 G07
U W
2.7
3400 G04
V
OUT
vs Temperature
FIGURE 1 CIRCUIT
I
O
= 10mA
1.4
1.3
1.2
1.1
1.0
0.9
0.8
–30
0
30
60
TEMPERATURE (°C)
90
120
3400 G02
Minimum Start-Up Voltage
vs Load Current
T
A
= 25°C
3.24
–60
0.1
1
10
I
OUT
(mA) CURRENT SOURCE LOAD
100
3400 G03
Normalized Oscillator Frequency
vs Temperature
1.01
1.00
0.99
0.98
0.97
0.96
0.95
–50 –30
SW Pin Antiringing Operation
V
SW
1V/DIV
0V
V
IN
= 1.3V
V
OUT
= 3.3V
I
OUT
= 10mA
L = 6.8µH
C
OUT
= 4.7µF
100ns/DIV
3400 G06
3.0
30
50
–10 10
TEMPERATURE (°C)
70
90
3400 G05
Fixed Frequency and Burst Mode
Operation
V
OUT
Transient Response
V
OUT(AC)
100mV/DIV
60mA
10µA
V
IN
= 1.3V
10ms/DIV
V
OUT
= 3.3V
I
OUT
= 60mA TO 10µA
L = 6.8µH
C
OUT
= 4.7µF
3400 G08
V
OUT(AC)
100mV/DIV
100mA
I
OUT
40mA
V
IN
= 1.3V
100µs/DIV
V
OUT
= 3.3V
I
OUT
= 40mA TO 100mA
L = 6.8µH
C
OUT
= 4.7µF
3400 G09
I
OUT
34001f
3
LTC3400-1
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 100Ω 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 < 1µA.
100Ω connected between SW and V
IN
. V
IN
is connected
to V
OUT
through the internal P-channel MOSFET syn-
chronous rectifier and external inductor.
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 connected to V
IN
in shutdown through the internal
P-channel MOSFET synchronous rectifier.
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.
BLOCK DIAGRA
+
SINGLE
CELL
INPUT
6
V
IN
V
OUT
GOOD
START-UP
OSC
A
B
A/B
MUX
PWM
CONTROL
RAMP
GEN
1.2MHz
PWM
COMPARATOR
SHUTDOWN
SYNC
DRIVE
CONTROL
SLOPE
COMP
Σ
SLEEP
Burst Mode
OPERATION
CONTROL
C
C
150pF
C
P2
2.5pF
SHDN
4
SHUTDOWN
CONTROL
SHUTDOWN
2
GND
34001 BD
4
+
R
C
80k
g
m
ERROR
AMP
–
–
+
–
–
+
W
U
U
U
L1
4.7µH
C
IN
1µF
1
SW
OPTIONAL
SCHOTTKY
2.3V
0.45Ω
V
OUT
5
3.3V
OUTPUT
0.35Ω
C
FF
(OPTIONAL)
R1
1.02M
1%
(EXTERNAL)
CURRENT
SENSE
FB
3
1.23V
REF
C
OUT
4.7µF
R2
604k
1%
(EXTERNAL)
34001f
LTC3400-1
OPERATIO
The LTC3400-1 is a1.2MHz, synchronous boost converter
housed in a 6-lead ThinSOT package. Able to operate from
an input voltage below 1V, the device features 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 device maintains 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 LTC3400-1 will start up at a typical V
IN
voltage 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 1.5µs off-
time during start-up, allowing the device to start up into an
output load. Once V
OUT
exceeds 2.3V, the start-up cir-
cuitry is disabled and normal fixed frequency PWM opera-
tion is initiated. In this mode, the LTC3400-1 operates
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
U
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 LTC3400-1 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 LTC3400-1 draws only
19µA from the output capacitor, greatly enhancing effi-
ciency. When the output voltage has drooped approxi-
mately 1% from nominal, the LTC3400-1 wakes up and
commences normal PWM operation. The output capacitor
recharges and causes the LTC3400-1 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 LTC3400-1
turns on less frequently. When the load current increases
34001f
5
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