FEATURES
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LTC3251/
LTC3251-1.2/LTC3251-1.5
500mA High Efficiency,
Low Noise, Inductorless
Step-Down DC/DC Converter
DESCRIPTIO
The LTC
®
3251/LTC3251-1.2/LTC3251-1.5 are 2-phase
charge pump step-down DC/DC converters that produce a
regulated output from a 2.7V to 5.5V input. The parts use
switched capacitor fractional conversion to achieve twice
the typical efficiency of a linear regulator. No inductors are
required. V
OUT
is resistor programmable from 0.9V to 1.6V
or fixed at 1.2V or 1.5V, with up to 500mA of load current
available.
A unique 2-phase spread spectrum architecture provides
a very low noise regulated output as well as low noise at the
input.* The parts have four operating modes: Continuous
Spread Spectrum, Spread Spectrum with Burst Mode
operation, Super Burst
TM
mode operation and shutdown.
Low operating current (35µA in Burst Mode operation,
10µA in Super Burst mode operation) and low external
parts count make the LTC3251/LTC3251-1.2/LTC3251-1.5
ideally suited for space-constrained battery-powered
applications. The parts are short-circuit and overtempera-
ture protected, and are available in a thermally enhanced
10-pin MSOP package.
, LTC and LT are registered trademarks of Linear Technology Corporation.
Burst Mode is a registered trademark of Linear Technology Coareoration.
Super Burst is a trademark of Linear Technology Corporation.
*U.S. Patent #6, 411, 531
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Up to 500mA Output Current
No Inductors
2.7V to 5.5V Input Voltage Range
2x Efficiency Improvement Over LDOs
2-Phase, Spread Spectrum Operation
for Low Input and Output Noise
Shutdown Disconnects Load from V
IN
Adjustable Output Voltage Range: 0.9V to 1.6V
Fixed Output Voltages: 1.2V, 1.5V
Super Burst, Burst and Burst Defeat Operating Modes
Low Operating Current: I
IN
= 35µA (Burst Mode
®
Operation)
Super Burst Operating Current: I
IN
= 10µA
Low Shutdown Current: I
IN
= 0.01µA Typ
Soft-Start Limits Inrush Current at Turn-On
Short-Circuit and Overtemperature Protected
Available in a Thermally Enhanced
10-Pin MSOP Package
APPLICATIO S
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Handheld Devices
Cellular Phones
Portable Electronic Equipment
DSP Power Supplies
TYPICAL APPLICATIO
OFF ON
100
Spread Spectrum Step-Down Converter
EFFICIENCY (%)
1
9
MD0 MD1
1-CELL Li-Ion
OR
3-CELL NiMH
LTC3251-1.5
7
V
IN
V
OUT
3
8
C1
+
C2
+
1µF 4
6
C2
–
C1
–
5, 11
10
GND
MODE
2
V
OUT
= 1.5V
500mA
10µF
1µF
90
80
70
60
50
40
30
20
10
3251 TA01
1µF
0
U
3
U
U
1.5V Efficiency vs Input Voltage
(Burst Mode Operation)
I
OUT
= 200mA
LTC3251-1.5
LDO
3.5
4.5
4
INPUT VOLTAGE (V)
5
5.5
3251 TA02
32511215fa
1
LTC3251/
LTC3251-1.2/LTC3251-1.5
ABSOLUTE
(Notes 1, 7)
AXI U
RATI GS
Operating Temperature Range (Note 3) ... –40°C to 85°C
Storage Temperature Range .................. – 65°C to 150°C
Lead Temperature (Soldering, 10 sec)................... 300°C
V
IN
to GND ................................................... –0.3V to 6V
MD0, MD1, MODE and FB to GND . – 0.3V to (V
IN
+ 0.3V)
I
OUT
(Note 2) ...................................................... 650mA
PACKAGE/ORDER I FOR ATIO
TOP VIEW
MD0
V
IN
C1
+
C1
–
GND
1
2
3
4
5
10
9
8
7
6
FB
MD1
C2
+
V
OUT
C2
–
11
ORDER PART
NUMBER
LTC3251EMSE
MSE PART MARKING
LTB4
MSE PACKAGE
10-LEAD PLASTIC MSOP
EXPOSED PAD IS GND (PIN 11),
MUST BE SOLDERED TO PCB
T
JMAX
= 125°C,
θ
JA
= 40°C/W,
θ
JC
= 10°C/W
Consult LTC Marketing for parts specified with wider operating temperature ranges.
ELECTRICAL CHARACTERISTICS
PARAMETER
V
IN
Minimum Operating Voltage
V
IN
Maximum Operating Voltage
V
IN
Continuous Mode Operating Current
V
IN
Burst Mode Operating Current
V
IN
Super Burst Mode Operating Current
V
IN
Shutdown Current
V
FB
Regulation Voltage (LTC3251)
V
OUT
Regulation Voltage (LTC3251-1.2)
Continuous Mode or Burst Mode Operation
V
OUT
Regulation Voltage (LTC3251-1.2)
Super Burst Operation
V
OUT
Regulation Voltage (LTC3251-1.5)
Continuous Mode or Burst Mode Operation
The
q
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
IN
= 3.6V, C1 = C2 = 1µF, C
IN
= 1µF, C
OUT
= 10µF,
V
MODE
= 0V for LTC3251-1.2V or LTC3251-1.5, V
OUT
= 1.5V for LTC3251, all capacitors ceramic, unless otherwise noted.
CONDITIONS
(Notes 4,5)
(Note 5)
I
OUT
= 0mA, V
MD0
= 0, V
MD1
= V
IN
Spread Spectrum Disabled MODE = V
IN
I
OUT
= 0mA, V
MD0
= V
IN
, V
MD1
= 0
Spread Spectrum Disabled MODE = V
IN
I
OUT
= 0mA, V
MD0
= V
IN
, V
MD1
= V
IN
Spread Spectrum Disabled MODE = V
IN
V
MD0
= 0V, V
MD1
= 0V (Note 5)
I
OUT
= 0mA, 2.7V
≤
V
IN
≤
5.5V
I
OUT
≤
200mA, 2.7V
≤
V
IN
≤
5.5V (Note 5)
I
OUT
≤
300mA, 2.8V
≤
V
IN
≤
5.5V (Note 5)
I
OUT
≤
500mA, 3V
≤
V
IN
≤
5.5V (Note 5)
I
OUT
≤
40mA
I
OUT
≤
100mA, 3.1V
≤
V
IN
≤
5.5V (Note 5)
I
OUT
≤
200mA, 3.2V
≤
V
IN
≤
5.5V (Note 5)
I
OUT
≤
300mA, 3.3V
≤
V
IN
≤
5.5V (Note 5)
I
OUT
≤
500mA, 3.5V
≤
V
IN
≤
5.5V (Note 5)
I
OUT
≤
40mA
V
MD0
= 0, V
MD1
= V
IN
or V
MD0
= V
IN
, V
MD1
= 0
V
MD0
= V
IN
, V
MD1
= V
IN
0mA
≤
I
OUT
≤
500mA, Referred to FB Pin
q
q
q
q
q
q
q
q
q
q
q
q
q
q
q
q
q
q
q
V
OUT
Regulation Voltage (LTC3251-1.5)
Super Burst Operation
I
OUT
Continuous Output Current (LTC3251)
I
OUT
Super Burst Output Current (LTC3251)
Load Regulation (LTC3251)
2
U
U
W
W W
U
W
TOP VIEW
MD0
V
IN
C1
+
C1
–
GND
1
2
3
4
5
10
9
8
7
6
MODE
MD1
C2
+
V
OUT
C2
–
ORDER PART
NUMBER
LTC3251EMSE-1.2
LTC3251EMSE-1.5
MSE PART MARKING
LTAGM
LTABE
11
MSE PACKAGE
10-LEAD PLASTIC MSOP
EXPOSED PAD IS GND (PIN 11),
MUST BE SOLDERED TO PCB
T
JMAX
= 125°C,
θ
JA
= 40°C/W,
θ
JC
= 10°C/W
MIN
2.7
TYP
MAX
5.5
UNITS
V
V
mA
mA
µA
µA
µA
µA
µA
V
V
V
V
V
V
V
V
V
V
mA
mA
3
3.75
35
35
10
10
0.01
0.78
1.15
1.15
1.15
1.15
1.44
1.44
1.44
1.44
1.44
500
40
0.045
0.8
1.2
1.2
1.2
1.2
1.5
1.5
1.5
1.5
1.5
5
6
60
60
15
15
1
0.82
1.25
1.25
1.25
1.25
1.56
1.56
1.56
1.56
1.56
mV/mA
32511215fa
LTC3251/
LTC3251-1.2/LTC3251-1.5
ELECTRICAL CHARACTERISTICS
PARAMETER
Line Regulation (LTC3251)
Spread Spectrum Frequency Range
Spread Spectrum Disabled Frequency
MD0, MD1 Input High Voltage
MD0, MD1 Input Low Voltage
MD0, MD1 Input High Current
MD0, MD1 Input Low Current
FB Input Current (LTC3251)
MODE Input High Voltage (LTC3251-1.2/LTC3251-1.5)
MODE Input Low Voltage (LTC3251-1.2/LTC3251-1.5)
MODE Input High Current (LTC3251-1.2/LTC3251-1.5)
MODE Input Low Current (LTC3251-1.2/LTC3251-1.5)
Turn-On Time (Burst or Continuous Mode Operation)
Open-Loop Output Impedance (LTC3251)
The
q
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
IN
= 3.6V, C1 = C2 = 1µF, C
IN
= 1µF, C
OUT
= 10µF,
V
MODE
= 0V for LTC3251-1.2V or LTC3251-1.5, V
OUT
= 1.5V for LTC3251, all capacitors ceramic, unless otherwise noted.
CONDITIONS
I
OUT
= 500mA, 2.7V
≤
V
IN
≤
5.5V
f
MIN
Switching Frequency
f
MAX
Switching Frequency
MODE = V
IN
2.7V
≤
V
IN
≤
5.5V
2.7V
≤
V
IN
≤
5.5V
MD0 = V
IN
, MD1 = V
IN
MD0 = 0V, MD1 = 0V
V
FB
= 0.85V
2.7V
≤
V
IN
≤
5.5V
2.7V
≤
V
IN
≤
5.5V
MODE = V
IN
MODE = 0V
R
OL
= 3Ω, (Note 5)
V
IN
= 3V, I
OUT
= 200mA (Note 6)
q
q
q
q
q
q
q
q
q
q
q
q
q
MIN
0.7
1.3
0.4
–1
–1
–50
TYP
0.2
1.0
1.6
1.6
0.8
0.8
MAX
UNITS
%/V
MHz
MHZ
MHz
V
V
µA
µA
nA
%/V
IN
%/V
IN
µA
µA
ms
Ω
2
2
1.2
1
1
50
50
30
–1
–1
1
0.45
50
70
1
1
0.7
Note 1:
Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired.
Note 2:
Based on long term current density limitations.
Note 3:
The LTC3251E is guaranteed to meet specified performance 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 4:
Minimum operating voltage required for regulation is:
V
IN
≥
2 • (V
OUT
+ R
OL
• I
OUT
)
Note 5:
V
MODE
= 0V or V
MODE
= V
IN
for LTC3251-1.2/LTC3251-1.5.
Note 6:
Output not in regulation; R
OL
= (V
IN
/2 – V
OUT
)/I
OUT
.
(V
FB
= 0.76V). Burst or continuous mode operation.
Note 7:
This IC includes overtemperature protection that is intended to
protect the device during momentary overload conditions. Junction
temperature will exceed 125°C when overtemperature protection is active.
Continuous operation above the specified maximum operating junction
temperature may impair device reliability.
TYPICAL PERFOR A CE CHARACTERISTICS
No Load Supply Current vs Supply
Voltage (Continuous Mode Spread
Spectrum Enabled)
7
6
5
I
IN
(mA)
–40°C
25°C
85°C
I
IN
(µA)
4
3
2
1
0
2.7
I
CC
(mA)
3.2
3.7
4.2
V
IN
(V)
4.7
U W
5.2
3251 G01
No Load Supply Current vs Supply
Voltage (Continuous Mode,
Spread Spectrum Disabled)
10
9
8
7
6
5
4
3
2
1
0
2.7
3.2
3.7
4.2
V
IN
(V)
4.7
5.2
3251 G17
No Load Supply Current vs Supply
Voltage (Burst Mode Operation)
50
–40°C
25°C
85°C
45
85°C
40
25°C
35
–40°C
30
25
20
2.7
3.2
3.7
4.2
V
IN
(V)
4.7
5.2
3251 G02
32511215fa
3
LTC3251/
LTC3251-1.2/LTC3251-1.5
TYPICAL PERFOR A CE CHARACTERISTICS
No Load Supply Current
vs Supply Voltage
(Super Burst Mode Operation)
20
18
16
14
V
OUT
(V)
I
CC
(µA)
10
8
6
4
2
0
2.7
3.2
3.7
4.2
V
IN
(V)
4.7
25°C
–40°C
1.50
1.48
1.46
1.44
1.42
I
OUT
= 250mA
I
OUT
= 500mA
V
OUT
(V)
12
1.5V Output Voltage
vs Supply Voltage
(Super Burst Mode Operation)
1.60
1.58
1.56
1.54
1.30
T
A
= 25°C
0mA
10mA
40mA
1.28
1.26
1.24
V
OUT
(V)
V
OUT
(V)
1.50
1.48
1.46
1.44
1.42
1.40
3
3.5
4
4.5
V
IN
(V)
5
5.5
3251 G06
1.20
1.18
1.16
1.14
1.12
1.10
2.7
3.2
3.7
4.2
V
IN
(V)
4.7
5.2
3251 G18
V
FB
(V)
1.52
1.5V Output Efficiency vs Output
Current (Burst Mode Operation)
100
90
80
V
IN
= 3.3V
V
IN
= 3.6V
100
90
80
EFFICIENCY (%)
EFFICIENCY (%)
60
50
40
30
20
10
0
V
IN
= 4V
V
IN
= 5V
EFFICIENCY (%)
70
MD0 = V
IN
, MD1 = 0V
0.1
1
10
I
OUT
(mA)
100
1000
3251 G08
4
U W
85°C
5.2
3251 G02
1.5V Output Voltage vs Supply
Voltage (Burst Mode Operation/
Continuous Mode)
1.60
1.58
1.56
1.54
1.52
I
OUT
= 0mA
1.300
1.2V Output Voltage vs Supply
Voltage (Burst Mode Operation/
Continuous Mode)
1.280
1.260
1.240
1.220
1.200
1.180
1.160
1.140
1.120
I
OUT
= 500mA
I
OUT
= 250mA
I
OUT
= 0mA
T
A
= 25°C
T
A
= 25°C
1.40
3
3.5
4
4.5
V
IN
(V)
5
5.5
3251 G04
1.100
2.7
3.2
3.7
4.2
V
IN
(V)
4.7
5.2
3251 G05
1.2V Output Voltage
vs Supply Voltage
(Super Burst Mode Operation)
T
A
= 25°C
0mA
10mA
40mA
0.805
FB Voltage vs Output Current
(Burst Mode Operation/
Continuous Mode)
T
A
= 25°C
V
OUT
= 1.5V
0.800
1.22
0.795
0.790
0.785
0.780
0
100
200
300
400
I
OUT
(mA)
500
600
3251 G07
1.2V Output Efficiency vs Output
Current (Burst Mode Operation)
100
V
IN
= 3V
V
IN
= 2.7V
90
80
V
IN
= 3.5V
V
IN
= 4.5V
70
60
50
40
30
20
10
MD0 = V
IN
, MD1 = 0V
1
10
I
OUT
(mA)
100
1000
3251 G19
1.5V Output Efficiency vs Output
Current (Super Burst Mode
Operation)
V
IN
= 3.6V
V
IN
= 3.3V
70
60
50
40
30
20
10
0
0.1
V
IN
= 4V
V
IN
= 5V
0
MD0 = MD1 = V
IN
0.1
1
I
OUT
(mA)
3251 G09
10
100
32511215fa
LTC3251/
LTC3251-1.2/LTC3251-1.5
TYPICAL PERFOR A CE CHARACTERISTICS
MD0/MD1 Input Threshold Voltage
vs Supply Voltage
1.2
1.1
MD0/MD1 THRESHOLD (V)
1.0
0.9
0.8
0.7
0.6
0.5
0.4
2.7
3.2
3.7
4.2
V
IN
(V)
4.7
5.2
3251 G10
–40°C
25°C
85°C
FREQUENCY (MHz)
Output Transient Response
(Continuous Mode)
I
OUT
450mA
50mA
I
OUT
450mA
50mA
V
OUT
20mV/DIV
(AC)
T
A
= 25°C
10µs/DIV
C
OUT
= 10µF X5R 6.3V
V
OUT
= 1.5V
Supply Transient Response
(Continuous Mode)
V
IN
4.5V
3.5V
SPREAD
SPECT
ENABLED
10mV/DIV (AC)
V
OUT
20mV/DIV (AC)
20µs/DIV
T
A
= 25°C
C
OUT
= 10µF X5R 6.3V
I
OUT
= 250mA
V
OUT
= 1.5V
U W
Max/Min Oscillator Frequency
vs Supply Voltage
2.0
1.9
1.8
1.7
1.6
1.5
1.4
1.3
1.2
1.1
1.0
0.9
0.8
2.7
3.2
3.7
85°C MIN
4.2
V
IN
(V)
4.7
5.2
3251 G11
–40°C MAX
25°C MAX
85°C MAX
25°C MIN
–40°C MIN
Output Transient Response
(Burst Mode Operation)
V
IN
V
OUT
20mV/DIV
(AC)
V
OUT
20mV/DIV
(AC)
3251 G13
10µs/DIV
T
A
= 25°C
C
OUT
= 10µF X5R 6.3V
V
OUT
= 1.5V
3251 G14
LTC3251-1.5 Output Voltage
Ripple
SPREAD
SPECT
DISABLED
10mV/DIV (AC)
200ns/DIV
T
A
= 25°C
C
OUT
= 10µF X5R 6.3V
I
OUT
= 500mA
V
OUT
= 1.5V
3251 G15
3251 G16
32511215fa
5
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