LTC1503-1.8/LTC1503-2
High Efficiency Inductorless
Step-Down DC/DC Converters
FEATURES
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DESCRIPTIO
Input Voltage Range: 2.4V to 6V
Fixed Output Voltages: 1.8V
±4%,
2V
±4%
Output Current: Up to 100mA
No Inductors
Typical Efficiency 25% Higher than LDOs
Low Operating Current: 25
µ
A
Low Shutdown Current: 5
µ
A
600kHz Switching Frequency
Shutdown Disconnects Load from V
IN
Soft-Start Limits Inrush Current at Turn-On
Short-Circuit and Overtemperature Protected
Available in 8-Pin MSOP and SO Packages
The LTC
®
1503-1.8/LTC1503-2 are switched capacitor
step-down DC/DC converters that produce a regulated
output from a 2.4V to 6V input. The parts use switched
capacitor fractional conversion to achieve high efficiency
over the entire input range. No inductors are required.
Internal circuitry controls the step-down conversion ratio
to optimize efficiency as the input voltage and load condi-
tions vary. Typical efficiency is 25% higher than that of a
low dropout (LDO) linear regulator.
Regulation is achieved by sensing the output voltage and
enabling the internal switching network as needed to
maintain a fixed output voltage. This method of regulation
enables the parts to achieve high efficiency at extremely
light loads. Low operating current (25µA with no load, 5µA
in shutdown) and low external parts count (two 1µF flying
capacitors and two 10µF bypass capacitors) make the
LTC1503-1.8/LTC1503-2 ideally suited for space con-
strained battery-powered applications. The parts are fully
short-circuit and overtemperature protected.
The LTC1503-1.8/LTC1503-2 are available in 8-pin MSOP
and SO packages.
, LTC and LT are registered trademarks of Linear Technology Corporation.
APPLICATIO S
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Cellular Phones
Handheld Computers
Smart Card Readers
Low Power DSP Supplies
Portable Electronic Equipment
Handheld Medical Instruments
TYPICAL APPLICATIO
Single Li-Ion to 2V DC/DC Converter
80
4
1-CELL Li-Ion OR
3-CELL NiMH
10µF
1µF
2
3
5
V
IN
C1
–
C1
+
V
OUT
C2
–
C2
+
1
8
6
7
1µF
10µF
V
OUT
= 2V
I
OUT
= 100mA
EFFICIENCY (%)
LTC1503-2
SHDN/SS GND
1503-1.8/2 TA01
U
Efficiency vs Input Voltage
100
I
OUT
= 100mA
I
OUT
= 1mA
60
“IDEAL” LDO
40
LTC1503-2
V
OUT
= 2V
20
2
3
4
INPUT VOLTAGE (V)
1503-1.8/2 TA02
U
U
5
6
1
LTC1503-1.8/LTC1503-2
ABSOLUTE
AXI U
RATI GS
V
IN
, C1
+
, C1
–
, C2
+
, C2
–
to GND ............... – 0.3V to 6.5V
SHDN/SS to GND ......................... – 0.3V to (V
IN
+ 0.3V)
V
OUT
Short-Circuit Duration ............................. Indefinite
Commercial Temperature Range ............ – 40°C to 85°C
PACKAGE/ORDER I FOR ATIO
TOP VIEW
V
OUT
C1
–
C1
+
V
IN
1
2
3
4
8 C2
–
7 GND
6 C2
+
5 SHDN/SS
ORDER PART
NUMBER
LTC1503CMS8-1.8
LTC1503CMS8-2
MS8 PART MARKING
LTFX
LTHN
V
OUT
1
C1
–
2
C1
+
3
V
IN
4
MS8 PACKAGE
8-LEAD PLASTIC MSOP
T
JMAX
= 125°C,
θ
JA
= 200°C/W
Consult factory for Military grade parts.
ELECTRICAL CHARACTERISTICS
The
q
denotes specifications which apply over the full operating temperature range, otherwise specifications are at T
A
= 25°C.
V
IN
= V
IN(MIN)
to V
IN(MAX)
, C1 = C2 = 1µF, C
IN
= C
OUT
= 10µF unless otherwise noted.
PARAMETER
V
IN
Operating Voltage
V
OUT
V
IN
Operating Current
V
IN
Shutdown Current
Output Ripple Voltage
Efficiency
Switching Frequency
SHDN/SS Input Threshold
SHDN/SS Input Current
V
OUT
Short-Circuit Current
V
OUT
Turn-On Time
V
SHDN/SS
= 0V (Note 3)
V
SHDN/SS
= V
IN
V
OUT
= 0V (Note 4)
C
SS
= 0nF, V
IN
= 3.6V, C
OUT
= 10µF
C
SS
= 10nF
LTC1503-1.8, 0mA < I
OUT
< 100mA
LTC1503-2, 0mA < I
OUT
< 100mA
I
OUT
= 0mA
SHDN/SS = 0V
LTC1503-X, V
IN
= 3.6V, I
OUT
= 100mA
LTC1503-2, V
IN
= 3.6V, I
OUT
= 100mA
Oscillator Free Running
q
q
q
q
CONDITIONS
q
q
q
q
q
Note 1:
Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired.
Note 2:
The LTC1503C is guaranteed to meet specified performance from
0°C to 70°C and is designed, characterized and expected to meet these
extended temperature limits, but are not tested at – 40°C and 85°C. The
LTC1503I is guaranteed to meet the extended temperature limits.
2
U
U
W
W W
U
W
(Note 1)
Industrial Temperature Range ............... – 40°C to 85°C
Specified Temperature Range (Note 2) ... – 40°C to 85°C
Storage Temperature Range ................ – 65°C to 150°C
Lead Temperature (Soldering, 10 sec)................. 300°C
TOP VIEW
8 C2
–
7 GND
6 C2
+
5 SHDN/SS
ORDER PART
NUMBER
LTC1503CS8-1.8
LTC1503CS8-2
LTC1503IS8-1.8
LTC1503IS8-2
S8 PART MARKING
150318
15032
503I18
1503I2
S8 PACKAGE
8-LEAD PLASTIC SO
T
JMAX
= 125°C,
θ
JA
= 150°C/W
MIN
2.4
1.728
1.920
TYP
1.8
2.0
25
5
25
82.9
600
MAX
6
1.872
2.080
50
10
UNITS
V
V
V
µA
µA
mV
P-P
%
kHz
0.2
– 3.5
–1
8
0.35
–2
22
0.1
8
0.5
–1
1
50
V
µA
µA
mA
ms
ms
Note 3:
Currents flowing into the device are positive polarity. Currents
flowing out of the device are negative polarity.
Note 4:
When V
OUT
is less than 150mV, I
OUT
is limited to much less than
the maximum rated output current to prevent damage to the output
devices.
LTC1503-1.8/LTC1503-2
TYPICAL PERFOR A CE CHARACTERISTICS
LTC1503-X Input Operating
Current vs Input Voltage
50
I
OUT
= 0mA
10
INPUT SHUTDOWN CURRENT (µA)
T
A
= –40°C
5
T
A
= 25°C
T
A
= 85°C
OUTPUT VOLTAGE (V)
INPUT CURRENT (µA)
40
30
T
A
= 25°C
20
T
A
= –40°C
T
A
= 85°C
10
2
3
4
INPUT VOLTAGE (V)
LTC1503-2
Output Voltage vs Input Voltage
2.10
I
OUT
= 50mA
2.05
EFFICIENCY (%)
OUTPUT VOLTAGE (V)
T
A
= –40°C
2.00
T
A
= 85°C
T
A
= 25°C
1.95
I
OUT
= 1mA
60
“IDEAL”
LDO
40
EFFICIENCY (%)
1.90
2
3
4
INPUT VOLTAGE (V)
5
LTC1503-2
Efficiency vs Output Current
100
T
A
= 25°C
1.84
80
OUTPUT VOLTAGE (V)
EFFICIENCY (%)
T
A
= –40°C
1.80
T
A
= 85°C
1.78
T
A
= 25°C
OUTPUT VOLTAGE (V)
60
40
V
IN
= 5V
V
IN
= 4.4V
V
IN
= 3.6V
V
IN
= 3V
V
IN
= 2.4V
0.1
10
100
1
OUTPUT CURRENT (mA)
1000
20
0
0.01
U W
5
1503 G01
LTC1503-X Input Shutdown
Current vs Input Voltage
1.90
V
OUT
= 0V
V
SHDN
/SS = 0V
7.5
1.85
LTC1503-1.8
Output Voltage vs Input Voltage
I
OUT
= 50mA
T
A
= –40°C
1.80
T
A
= 25°C
1.75
T
A
= 85°C
2.5
6
0
1.70
2
3
4
INPUT VOLTAGE (V)
1503-1.8/2 TA02
5
6
2
3
4
INPUT VOLTAGE (V)
5
6
1503-1.8/2 G03
LTC1503-1.8
Efficiency vs Input Voltage
100
T
A
= 25°C
100
LTC1503-1.8
Efficiency vs Output Current
T
A
= 25°C
I
OUT
= 100mA
80
80
60
40
V
IN
= 5V
V
IN
= 4.4V
V
IN
= 3.6V
V
IN
= 3V
V
IN
= 2.4V
0.1
10
100
1
OUTPUT CURRENT (mA)
1000
20
6
1503 G03
20
2
3
4
INPUT VOLTAGE (V)
5
6
1503-1.8/2 G05
0
0.01
1503-1.8/2 G06
LTC1503-1.8
Output Voltage vs Output Current
V
IN
= 3.3V
LTC1503-2
Output Voltage vs Output Current
2.04
V
IN
= 3.3V
1.82
2.02
T
A
= –40°C
2.00
T
A
= 85°C
1.98
T
A
= 25°C
1.76
1.96
1.74
0.01
0.1
10
100
1
OUTPUT CURRENT (mA)
1000
1.94
0.01
0.1
10
100
1
OUTPUT CURRENT (mA)
1000
1503-1.8/2 G07
1503-1.8/2 G08
1503-1.8/2 G09
3
LTC1503-1.8/LTC1503-2
TYPICAL PERFOR A CE CHARACTERISTICS
LTC1503-X Output Short-Circuit
Current vs Input Voltage
40
V
OUT
SHORTED TO GND
100
OUTPUT CURRENT (mA)
T
A
= –40°C
20
T
A
= 85°C
10
START-UP TIME (ms)
30
0
2
Output Load Transient Response
(LTC1503-1.8,1mA to 100mA Step)
100mA
I
OUT
50mA/DIV
1mA
V
OUT
50mV/DIV
AC COUPLED
1ms/DIV
1503-1.8/2 G12
PI FU CTIO S
V
OUT
(Pin 1):
Regulated Output Voltage. V
OUT
is discon-
nected from V
IN
during shutdown. Bypass V
OUT
to ground
with a
≥
10µF low ESR capacitor.
C1
–
(Pin 2):
Flying Capacitor One Negative Terminal.
C1
+
(Pin 3):
Flying Capacitor One Positive Terminal.
V
IN
(Pin 4):
Input Voltage. V
IN
may be between 2.4V and
6V. Bypass V
IN
to ground with a
≥10µF
low ESR capacitor.
SHDN/SS (Pin 5):
Shutdown/Soft-Start Control. The pin
is designed to be driven with an external open-drain
output. Holding the SHDN/SS pin below 0.25V will force
the part into shutdown mode. An internal pull-up current
of 2µA will force the SHDN/SS 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 SHDN/SS pin and ground. Capacitance on
the SHDN/SS 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 for a known output
capacitor, the user can control the inrush current during
4
U W
3
LTC1503-X Start-Up Time
vs Soft-Start Capacitor
V
IN
= 3.6V
10
T
A
= –40°C
1
T
A
= 25°C
T
A
= 85°C
0.1
T
A
= 25°C
4
INPUT VOLTAGE (V)
5
6
1503-1.8/2 G10
0.01
0.01
1
10
0.1
SOFT-START CAPACITOR (nF)
100
1503-1.8/2 G10
Output Ripple, C
OUT
= 10µF
Output Ripple, C
OUT
= 22µF
V
OUT
10mV/DIV
AC COUPLED
V
OUT
10mV/DIV
AC COUPLED
5µs/DIV
V
IN
= 3.6V
V
OUT
= 2V
I
OUT
= 100mA
C
OUT
= 10µF CERAMIC
1503-1.8/2 G13
5µs/DIV
V
IN
= 3.6V
V
OUT
= 2V
I
OUT
= 100mA
C
OUT
= 22µF CERAMIC
1503-1.8/2 G14
U
U
U
LTC1503-1.8/LTC1503-2
PI FU CTIO S
turn-on (see Applications Information). If neither of the
two functions are desired, the pin may be floated or tied
to V
IN
.
C2
+
(Pin 6):
Flying Capacitor Two Positive Terminal.
GND (Pin 7):
Ground. Connect to a ground plane for best
performance.
C2
–
(Pin 8):
Flying Capacitor Two Negative Terminal.
BLOCK DIAGRA
V
IN
C
IN
680k
330k
990k
SHORT CIRCUIT
MODE SKIP
600kHz
OSCILLATOR
V
IN
2µA
REG ENABLE
COMP1
SOFT-START
350mV
V
REF
RAMP
SHDN/SS
+
SHDN
350mV
+
–
LTC1503-2
1503-1.8/2 BD
+
COMP2
–
–
–
+
+
+
+
–
+
W
U
U
U
+
–
MODE
CONTROL
STEP-DOWN
CHARGE
PUMP
C1
+
C1
–
C2
+
+
–
V
OUT
C2
–
V
OUT
C
OUT
+
150mV
800k
10mV
1.2M
1.2V
V
REF
GND
5
嵌入式系统
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