LTC1911-1.5/LTC1911-1.8
Low Noise, High Efficiency,
Inductorless Step-Down
DC/DC Converter
FEATURES
s
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s
s
s
s
s
s
s
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DESCRIPTIO
Low Noise Constant Frequency Operation
2.7V to 5.5V Input Voltage Range
No Inductors
Typical Efficiency 25% Higher Than LDOs
Shutdown Disconnects Load from V
IN
Output Voltage: 1.8V
±4%
or 1.5V
±4%
Output Current: 250mA
Low Operating Current: I
IN
= 180µA Typ
Low Shutdown Current: I
IN
= 10µA Typ
Oscillator Frequency: 1.5MHz
Soft-Start Limits Inrush Current at Turn On
Short-Circuit and Overtemperature Protected
Available in an 8-Pin MSOP Package
The LTC
®
1911 is a switched capacitor step-down DC/DC
converter that produces a 1.5V or 1.8V regulated output
from a 2.7V to 5.5V input. The part uses switched capaci-
tor fractional conversion to achieve high efficiency over the
entire input range. No inductors are required. Internal cir-
cuitry controls the step-down conversion ratio to optimize
efficiency as the input voltage and load conditions vary.*
Typical efficiency is over 25% higher than that of a linear
regulator.
A unique constant frequency architecture provides a low
noise regulated output as well as lower input noise than
conventional charge pump regulators. High frequency
operation (f
OSC
= 1.5MHz) simplifies output filtering to
further reduce conducted noise. To optimize efficiency,
the part enters Burst Mode
®
operation under light load
conditions.
Low operating current (180µA with no load, 10µA in
shutdown) and low external parts count (two 1µF flying
capacitors and two 10µF bypass capacitors) make the
LTC1911 ideally suited for space constrained battery-
powered applications. The part is short-circuit and
overtemperature protected, and is available in an 8-pin
MSOP package.
APPLICATIO S
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Handheld Computers
Cellular Phones
Smart Card Readers
Portable Electronic Equipment
Handheld Medical Instruments
Low Power DSP Supplies
, LTC and LT are registered trademarks of Linear Technology Corporation.
Burst Mode is a registered trademark of Linear Technology Corporation.
*U.S. Patent #6,438,005
TYPICAL APPLICATIO
90
Single Cell Li-Ion to 1.8V DC/DC Converter
80
100mA
LTC1911-1.8
2.7V TO 5.5V INPUT
1-CELL Li-Ion
OR
3-CELL NiMH
10µF*
1µF*
1
2
3
4
*CERAMIC CAPACITOR
30
2
3
4
5
INPUT VOLTAGE (V)
6
1911 G05
V
IN
C2
+
C2
–
GND
SS/SHDN
V
OUT
C1
+
C1
–
8
6
7
5
1µF*
1911 TA01
EFFICIENCY (%)
70
60
50
IDEAL LDO
40
V
OUT
= 1.8V
V
OUT
= 1.8V
I
OUT
= 250mA
10µF*
U
Efficiency
250mA
1911f
U
U
1
LTC1911-1.5/LTC1911-1.8
ABSOLUTE
(Note 1)
AXI U
RATI GS
PACKAGE/ORDER I FOR ATIO
TOP VIEW
V
IN
C2
+
C2
–
GND
1
2
3
4
8
7
6
5
SS/SHDN
C1
+
V
OUT
C1
–
V
IN
to GND ...................................................– 0.3V to 6V
SS/SHDN to GND ........................ – 0.3V to (V
IN
+ 0.3V)
V
OUT
Short-Circuit Duration ............................ Indefinite
Operating Temperature Range (Note 2) .. – 40°C to 85°C
Storage Temperature Range ................. – 40°C to 150°C
Lead Temperature (Soldering, 10 sec).................. 300°C
ORDER PART
NUMBER
LTC1911EMS8-1.5
LTC1911EMS8-1.8
MS8 PART MARKING
LTMY
LTNU
MS8 PACKAGE
8-LEAD PLASTIC MSOP
T
JMAX
= 125°C,
θ
JA
= 160°C/ W
Consult LTC Marketing for parts specified with wider operating temperature ranges.
ELECTRICAL CHARACTERISTICS
PARAMETER
V
IN
Operating Voltage
V
OUT
V
IN
Operating Current
V
IN
Shutdown Current
Output Ripple
V
OUT
Short-Circuit Current
Switching Frequency
SS/SHDN Input Threshold
SS/SHDN Soft-Start Current
Turn-On Time
Load Regulation
Line Regulation
The
q
denotes specifications which apply over the full operating
temperature range, otherwise specifications are T
A
= 25°C. V
IN
= 3.6V, C1 = 1µF, C2 = 1µF, C
IN
= 10µF, C
OUT
= 10µF unless
otherwise noted.
CONDITIONS
q
MIN
2.7
1.44
1.73
q
q
q
q
TYP
1.5
1.8
180
10
5
12
600
MAX
5.5
1.56
1.87
350
20
UNITS
V
V
V
µA
µA
mV
P-P
mV
P-P
mA
LTC1911-1.5, 0mA
≤
I
OUT
≤
250mA, V
IN
= 2.7V to 5.5V
LTC1911-1.8, 0mA
≤
I
OUT
≤
250mA, V
IN
= 2.7V to 5.5V
I
OUT
= 0mA, V
IN
= 2.7V to 5.5V
SS/SHDN = 0V, V
IN
= 2.7V to 5.5V
I
OUT
= 10mA
I
OUT
= 250mA
V
OUT
= 0V
Oscillator Free Running
1.2
q
1.5
0.6
–2
0.01
0.03
10
0.13
0.3
1.8
1
–1
0.3
–5
V
SS/SHDN
= 0V (Note 3)
V
SS/SHDN
= V
IN
C
SS
= 0pF, V
IN
= 3.3V
C
SS
= 10nF, V
IN
= 3.3V
0V
≤
I
OUT
≤
250mA
0V
≤
I
OUT
≤
250mA
q
mV/mA
%/V
Note 1:
Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired.
Note 2:
The LTC1911E 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 3:
Currents flowing into the device are positive polarity. Currents
flowing out of the device are negative polarity.
2
U
MHz
V
µA
µA
ms
ms
1911f
W
U
U
W W
W
LTC1911-1.5/LTC1911-1.8
TYPICAL PERFOR A CE CHARACTERISTICS
Input Operating Current
vs Input Voltage
210
200
INPUT CURRENT (µA)
190
T
A
= 25°C
180
170
T
A
= –40°C
160
150
2
3
4
INPUT VOLTAGE (V)
1911 G01
11
T
A
= 25°C
T
A
= –40°C
OUTPUT VOLTAGE (V)
INPUT CURRENT (µA)
T
A
= 85°C
LTC1911-1.5
Output Voltage vs Input Voltage
1.55
I
OUT
= 250mA
T
A
= –40°C
T
A
= 25°C
1.53
T
A
= 85°C
100
90
OUTPUT VOLTAGE (V)
EFFICIENCY (%)
1.51
70
250mA
60
50
IDEAL LDO
40
EFFICIENCY (%)
1.49
1.47
30
1.45
2
3
4
INPUT VOLTAGE (V)
LTXXXX • TPCXX
5
LTC1911-1.5
Efficiency vs Output Current
90
80
OUTPUT VOLTAGE (V)
EFFICIENCY (%)
70
60
50
V
IN
:
40
30
2.8V
3.3V
3.7V
1
10
100
OUTPUT CURRENT (mA)
4.3V
5.1V
5.5V
1000
1911 G07
OUTPUT VOLTAGE (V)
U W
5
6
6
Input Shutdown Current
vs Input Voltage
15
V
OUT
= 0V
V
(SS/SHDN)
= 0V
T
A
= 85°C
1.90
LTC1911-1.8
Output Voltage vs Input Voltage
I
OUT
= 250mA
T
A
= –40°C
T
A
= 25°C
T
A
= 85°C
13
1.85
1.80
9
1.75
7
5
2
3
4
INPUT VOLTAGE (V)
1.70
5
6
1911 G02
2
3
4
INPUT VOLTAGE (V)
5
6
1911 G03
LTC1911-1.5 Efficiency vs Input
Voltage (Falling Input Voltage)
90
80
70
60
LTC1911-1.8
Efficiency vs Output Current
100mA
80
V
IN
:
50
40
30
2.7V
3.2V
3.7V
4.2V
5.1V
5.5V
1000
1911 G06
20
2
3
4
INPUT VOLTAGE (V)
5
6
1911 G05
1
100
10
OUTPUT CURRENT (mA)
LTC1911-1.8
Output Voltage vs Output Current
1.84
1.54
V
IN
= 3.6V
T
A
= –40°C
T
A
= 25°C
T
A
= 85°C
LTC1911-1.5
Output Voltage vs Output Current
V
IN
= 3.6V
T
A
= 85°C
T
A
= 25°C
1.82
1.52
1.80
1.50
T
A
= –40°C
1.78
1.48
1.76
1.46
1.74
0.1
10
1
100
OUTPUT CURRENT (mA)
1000
1911 G08
1.44
0.1
10
1
100
OUTPUT CURRENT (mA)
1000
1911 G09
1911f
3
LTC1911-1.5/LTC1911-1.8
TYPICAL PERFOR A CE CHARACTERISTICS
Start-Up Time
vs Soft-Start Capacitor
100
V
IN
= 3.6V
T
A
= –40°C
T
A
= 25°C
T
A
= 85°C
30
25
OUTPUT RIPPLE (mV
P-P
)
START-UP TIME (ms)
10
20
15
C
OUT
= 10µF
10
5
C
OUT
= 22µF
FREQUENCY (MHz)
1
0.1
0.1
1
10
SOFT-START CAPACITOR (nF)
LTC1911-1.8 Output Voltage Ripple
V
OUT
50mV/DIV
2-TO-1 MODE
V
IN
= 5V
V
OUT
50mV/DIV
3-TO-2 MODE
V
IN
= 3.6V
V
OUT
50mV/DIV
1-TO-1 MODE
V
IN
= 2.7V
I
OUT
= 250mA
100ns/DIV
ALL WAVEFORMS AC COUPLED
1911 G12
PI FU CTIO S
V
IN
(Pin 1):
Input Supply Voltage. V
IN
may be between
2.7V and 5.5V. Suggested bypass for V
IN
is a 10µF (1µF
min) ceramic low ESR capacitor.
C2
+
(Pin 2):
Flying Capacitor Two Positive Terminal.
C2
–
(Pin 3):
Flying Capacitor Two Negative Terminal.
GND (Pin 4):
Ground. Connect to a ground plane for best
performance.
C1
–
(Pin 5):
Flying Capacitor One Negative Terminal.
V
OUT
(Pin 6):
Regulated Output Voltage. V
OUT
is discon-
nected from V
IN
during shutdown. Bypass V
OUT
with a
≥
10µF ceramic low ESR capacitor (4µF min, ESR < 0.1Ω
max).
C1
+
(Pin 7):
Flying Capacitor One Positive Terminal.
SS/SHDN (Pin 8):
Soft-Start/Shutdown Control Pin. This
pin is designed to be driven with an external open-drain
output. Holding the SS/SHDN pin below 0.3V will force
the LTC1911-X into shutdown mode. An internal pull-up
current of 2µA will force the SS/SHDN voltage to climb to
V
IN
once the device driving the pin is forced into a Hi-Z
state. To limit inrush current on start-up, connect a
capacitor between the SS/SHDN pin and GND. Capaci-
tance on the SS/SHDN pin will limit the dV/dt of the pin
during turn on which, in turn, will limit the dV/dt of V
OUT
.
By selecting an appropriate soft-start capacitor, the user
can control the inrush current for a known output capaci-
tor during turn-on (see Application Information). If nei-
ther of the two functions are desired, the pin may be left
floating or tied to V
IN
.
1911f
4
U W
1911 G10
Output Ripple
vs Output Load Current
1.60
Oscillator Frequency
vs Input Supply Voltage
T
A
= –40°C
C
OUT
= 4.7µF
1.55
T
A
= 25°C
1.50
1.45
T
A
= 85°C
0
1.40
0
100
150
200
250
50
OUTPUT LOAD CURRENT (mA)
300
2.5
3.0
3.5
4.0
V
IN
(V)
4.5
5.0
5.5
1911 G15
100
1911 G11
Output Current Transient Response
250mA
I
OUT
25mA
4V
V
IN
500mV/DIV
3V
Line Transient Response
V
OUT
20mV/DIV
V
OUT
20mV/DIV
V
IN
= 3.6V
10µs/DIV
1911 G13
I
OUT
= 225mA
20µs/DIV
1911 G14
U
U
U
LTC1911-1.5/LTC1911-1.8
SI PLIFIED BLOCK DIAGRA
1
C
IN
V
IN
300k
+
50k
–
MODE
CONTROL
STEP-DOWN
CHARGE
PUMP
+
150k
SHDN
–
R
SENSE
ADJ
OFFSET
+
AMP1
–
V
REF
COMP1
OVERTEMP
DETECT
1.5MHz
OSCILLATOR
V
IN
2µA
8
600mV
+
1911 BD
+
SS/SHDN
SHDN
W
R
A
C1
+
7
C1
C1
–
–
W
5
C2
+
2
C2
3
C2
–
V
OUT
6
C
OUT
+
–
–
+
COMP2
BURST
THRESHOLD
60k
+
–
SHORT-CIRCUIT
THRESHOLD
–
AMP2
+
–
600mV
140k
SOFT-START
V
REF
RAMP
+
+
1.26V
V
REF
GND
4
1911f
5
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