FEATURES
s
s
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LTC3423/LTC3424
Low Output Voltage,
3MHz Micropower Synchronous
Boost Converters
DESCRIPTIO
The LTC
®
3423 and LTC3424 are high efficiency, fixed
frequency, step-up DC/DC converters that can regulate
output voltages as low as 1.5V from a single cell. An
applied voltage of at least 2.7V to the V
DD
pin is required
to power the internal control circuitry.
The devices include a 0.16Ω N-channel MOSFET switch
and a 0.21Ω P-channel synchronous rectifier. The LTC3423
is intended for applications requiring less than 0.75W of
output power and the LTC3424 for 1.5W or less. Switching
frequencies up to 3MHz are programmed with an external
timing resistor and the oscillator can be synchronized to
an external clock.
Quiescent current is only 38µA in Burst Mode operation,
maximizing battery life in portable applications. Burst
Mode operation is user controlled and can be enabled by
driving the MODE/SYNC pin high. If the MODE/SYNC pin
has either a clock or is driven low then the operation is at
constant fixed frequency.
Other features include a 1µA shutdown, thermal shutdown
and current limit. The LTC3423 and LTC3424 are available
in the 10-lead MSOP package. For applications requiring
an output voltage greater than 2.6V, the LTC3401 and
LTC3402 are recommended without the need of a separate
voltage for the V
DD
pin.
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1.5V to 5.5V Adjustable Output Voltage
Synchronous Rectification: Up to 95% Efficiency
1A Switch Current (LTC3423) or
2A Switch Current (LTC3424)
Fixed Frequency Operation Up to 3MHz
Wide Input Range: 0.5V to 5.5V (Operating)
Very Low Quiescent Current: 38µA (Burst Mode
®
Operation)
No External Schottky Diode Required
Synchronizable Switching Frequency
Burst Mode Enable Control
OPTI-LOOP
®
Compensation
Very Low Shutdown Current: < 1µA
Small 10-Pin MSOP Package
APPLICATIO S
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Pagers
Handheld Instruments
Cordless Phones
Wireless Handsets
GPS Receivers
Battery Backup
, LTC and LT are registered trademarks of Linear Technology Corporation.
Burst Mode and OPTI-LOOP are registered trademarks of Linear Technology Corporation.
TYPICAL APPLICATIO
V
DD
V
DD
= 2.7V TO 5.5V
V
IN
= 0.9V TO 1.5V
L1
2.2µH
1-Cell to 1.8V at 600mA Step-Up Converter
Efficiency
V
OUT
1.8V
600mA
SW
V
OUT
FB
4
7
EFFICIENCY (%)
100
90
Burst Mode
OPERATION
6
10
1
CELL
3
2
C1
2.2µF
C2
10µF
1
LTC3424
V
DD
SHDN
V
IN
R1
110k
C3
44µF
(2× 22µF)
C4
470pF
RC
82k
C5
4.7pF
R2
249k
80
70
60
50
40
30
20
10
0
0.1
+
–
8
9
5
MODE/SYNC V
C
R
t
GND
R
t
30.1k
0 = FIXED FREQ
1 = Burst Mode OPERATION
C1: TAIYO YUDEN JMK212BJ225MG
C2: TAIYO YUDEN JMK212BJ106MM
C3: TAIYO YUDEN JMK325BJ226MM
L1: SUMIDA CD43-2R2M
3423/24 TA01
U
U
U
V
IN
= 1.5V
V
IN
= 1.2V
V
IN
= 0.9V
V
DD
= 3.3V
V
OUT
= 1.8V
WITH MBRM120T3 SCHOTTKY
1
10
100
OUTPUT CURRENT (mA)
1000
3223/24 TA02
34234f
1
LTC3423/LTC3424
ABSOLUTE
(Note 1)
AXI U
RATI GS
PACKAGE/ORDER I FOR ATIO
TOP VIEW
R
t
MODE
V
IN
SW
GND
1
2
3
4
5
10
9
8
7
6
SHDN
V
C
FB
V
OUT
V
DD
V
IN
, V
OUT
, V
DD
Voltages .............................. – 0.5V to 6V
SW Voltage ................................................. – 0.5V to 6V
V
C
, R
t
Voltages ......................... – 0.5V to (V
OUT
+ 0.3V)
SHDN, FB, MODE Voltages ......................... – 0.5V to 6V
Operating Temperature Range (Note 2) .. – 40°C to 85°C
Storage Temperature Range ................. – 65°C to 125°C
Lead Temperature (Soldering, 10 sec).................. 300°C
ORDER PART
NUMBER
LTC3423EMS
LTC3424EMS
MS PART MARKING
LTQM
LTQN
MS PACKAGE
10-LEAD PLASTIC MSOP
T
JMAX
= 125°C
θ
JA
= 130°C/ W 1 LAYER BOARD
θ
JA
= 100°C/ W 4 LAYER BOARD
Consult LTC Marketing for parts specified with wider operating temperature ranges.
ELECTRICAL CHARACTERISTICS
The
q
denotes specifications that apply over the full operating temperature range, otherwise specifications are at T
A
= 25°C.
V
IN
= 1.2V, V
DD
= 3.3V, V
OUT
= 1.8V, unless otherwise noted.
PARAMETER
V
DD
Input Voltage Range
V
IN
Operating Voltage Range
Output Voltage Adjust Range
Feedback Voltage
Feedback Input Current
Quiescent Current—Burst Mode Operation
Quiescent Current—SHDN
Quiescent Current—Active
NMOS Switch Leakage
PMOS Switch Leakage
NMOS Switch On Resistance
PMOS Switch On Resistance
NMOS Current Limit
Maximum Duty Cycle
Minimum Duty Cycle
Frequency Accuracy
MODE/SYNC Input High
MODE/SYNC Input Low
MODE/SYNC Input Current
Error Amp Transconductance
V
MODE/SYNC
= 5.5V
∆I
= – 5µA to 5µA, V
C
= V
FB
0.01
85
R
t
= 15k
LTC3423
LTC3424
R
t
= 15k
q
q
q
q
q
CONDITIONS
q
MIN
2.7
0.5
1.5
1.22
q
q
q
TYP
MAX
5.5
5.5
5.5
UNITS
V
V
V
V
nA
µA
µA
µA
µA
µA
Ω
Ω
A
A
%
(Note 4)
1.25
1
38
0.1
440
0.1
0.1
0.16
0.21
1.28
50
65
1
800
5
10
V
FB
= 1.25V
V
C
= 0V, MODE/SYNC = 3.3V (Note 3)
SHDN = 0V, Not Including Switch Leakage
V
C
= 0V, MODE/SYNC = 0V, R
t
= 300k (Note 3)
1
2
80
1.6
1.4
1.6
2.8
85
0
2
2.4
0.4
1
µmhos
2
U
%
MHz
V
V
µA
34234f
W
U
U
W W
W
LTC3423/LTC3424
ELECTRICAL CHARACTERISTICS
The
q
denotes specifications that 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 noted.
PARAMETER
SHDN Input High
SHDN Input Low
SHDN Input Current
V
SHDN
= 5.5V
0.01
CONDITIONS
V
SHDN
= V
IN
= V
OUT
MIN
1
0.4
1
TYP
MAX
UNITS
V
V
µA
Note 1:
Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired.
Note 2:
The LTC3423/LTC3424 are guaranteed to meet performance
specifications from 0°C to 70°C. Specifications over the –40°C to 85°C
operating temperature range are assured by design, characterization and
correlation with statistical process controls.
Note 3:
Current is measured into V
DD
since the supply current is
bootstrapped to the V
DD
pin. The outputs are not switching.
Note 4:
Once the output is started, the IC is not dependant upon the V
IN
supply.
TYPICAL PERFOR A CE CHARACTERISTICS
Switching Waveform on SW Pin
Transient Response
150mA to 450mA
SW
0.5V/DIV
0V
I
LOAD
= 500mA
V
OUT
1.8V
100ns/DIV
3423/24 G01
Burst Mode Operation
at 500µA Load
V
OUT
100mV/DIV
AC COUPLED
V
OUT
100mV/DIV
AC COUPLED
SW
1V/DIV
1ms/DIV
V
IN
= 1.2V
V
OUT
= 1.8V
C
OUT
= 44µF
MODE/SYNC PIN = HIGH
U W
V
OUT
100mV/DIV
AC COUPLED
I
OUT
450mA
150mA
C
OUT
= 44µF
L = 2.2µH
f
OSC
= 1MHz
200µs/DIV
3423/24 G02
Burst Mode Operation
at 10mA Load
SW
1V/DIV
3423/24 G03
V
IN
= 1.2V
500µs/DIV
V
OUT
= 1.8V
C
OUT
= 44µF
MODE/SYNC PIN = HIGH
3423/24 G04
34234f
3
LTC3423/LTC3424
TYPICAL PERFOR A CE CHARACTERISTICS
Converter Efficiency 1.2V to 1.8V
100
90
80
EFFICIENCY (%)
300MHz
Burst Mode
OPERATION
3MHz
70
CURRENT (A)
60
50
40
30
20
10
0
0.1
1MHz
2.8
2.6
2.4
2.2
CURRENT (A)
WITH MBRM120T3 SCHOTTKY
10
100
1
OUTPUT CURRENT (mA)
1000
3223/24 G05
EA FB Voltage
1.28
1.27
2.05
2.10
FREQUENCY (MHz)
VOLTAGE (V)
1.26
1.25
1.24
1.23
1.22
–55
RESISTANCE (Ω)
–15
65
TEMPERATURE (°C)
25
PMOS R
DS(ON)
0.40
V
OUT
= 1.8V
V
DD
= 3.3V
14
12
0.35
EFFICIENCY LOSS (%)
RESISTANCE (Ω)
0.30
0.25
0.20
2
0.15
–55
0
0.2
–15
4
U W
3423/24 G08
LTC3424 Current Limit
3.4
3.2
3.0
1.80
1.75
1.70
1.65
1.60
1.55
1.50
1.45
–15
65
TEMPERATURE (°C)
25
105 125
3423/24 G06
LTC3423 Current Limit
2.0
–55
1.40
–55
–15
65
TEMPERATURE (°C)
25
105 125
3423/24 G07
Oscillator Frequency Accuracy
R
T
= 15k
0.30
NMOS R
DS(ON)
V
OUT
= 1.8V
V
DD
= 3.3V
0.25
0.20
2.00
0.15
1.95
0.10
105 125
1.90
–55
–15
65
TEMPERATURE (°C)
25
105 125
3423/24 G09
0.05
–55
–15
65
TEMPERATURE (°C)
25
105 125
3423/24 G10
Efficiency Loss Without Schottky
vs Frequency
T
A
= 25°C
10
8
6
4
65
TEMPERATURE (°C)
25
105 125
3423/24 G11
0.6
2.2
1.0 1.4 1.8
FREQUENCY (MHz)
2.6
3.0
3423/24
G12
34234f
LTC3423/LTC3424
TYPICAL PERFOR A CE CHARACTERISTICS
Shutdown Threshold
1.10
1.05
1.00
0.95
0.90
0.85
0.80
0.75
0.70
0.65
0.60
–55
–15
65
TEMPERATURE (°C)
25
105 125
3423/24 G13
CURRENT (µA)
VOLTAGE (V)
PI FU CTIO S
R
t
(Pin 1):
Timing Resistor to Program the Oscillator
Frequency.
f
OSC
3 • 10
10
=
Hz
R
t
MODE/SYNC (Pin 2):
Burst Mode Select and Oscillator
Synchronization.
MODE/SYNC = High. Enable Burst Mode operation. The
inductor peak inductor current will be 400mA and
return to zero current on each cycle. During Burst Mode
operation the operation is variable frequency, providing
a significant efficiency improvement at light loads. It is
recommended the Burst Mode operation only be en-
tered once the part has started up.
MODE/SYNC = Low. Disable Burst Mode operation and
maintain low noise, constant frequency operation.
MODE/SYNC = External CLK. Synchronization of the
internal oscillator and Burst Mode operation disable. A
clock pulse width of 100ns to 2µs is required to
synchronize.
V
IN
(Pin 3):
Voltage Sense for Internal Circuitry.
U W
Burst Mode Operation Current
44
42
40
38
36
34
32
30
–55
–15
65
TEMPERATURE (°C)
25
105 125
3423/24 G14
U
U
U
SW (Pin 4):
Switch Pin. Connect inductor and optional
Schottky diode here. Minimize trace length to keep EMI
down.
GND (Pin 5):
Signal and Power Ground for the IC.
V
DD
(Pin 6):
Power Source for the IC. Typically derived
from a higher voltage power converter. Requires an input
of 2.7V to 5.5V. A 2.2µF ceramic bypass capacitor is
recommended as close to the pins as possible.
V
OUT
(Pin 7):
Output of the Synchronous Rectifier.
FB (Pin 8):
Feedback Pin. Connect resistor divider tap
here. The output voltage can be adjusted from 1.5V to
5.5V. The feedback reference voltage is typically 1.25V.
V
C
(Pin 9):
Error Amp Output. A frequency compensation
network is connected to this pin to compensate the loop.
See the section “Compensating the Feedback Loop” for
guidelines.
SHDN (Pin 10):
Shutdown. Grounding this pin shuts down
the IC. Tie to >1V to enable (V
DD
or digital gate output).
During shutdown the output voltage will hold up to V
IN
minus a diode drop due to the body diode of the PMOS
synchronous switch. If the application requires a com-
plete disconnect during shutdown then refer to section
“Output Disconnect”.
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