LTC1517-3.3
Micropower, Regulated
3.3V Charge Pump in a
5-Pin SOT-23 Package
FEATURES
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DESCRIPTION
The LTC
®
1517-3.3 is a micropower charge pump DC/DC
converter that produces a regulated 3.3V output. The input
voltage range is 2V to 4.4V, allowing a single cell lithium
battery to produce a regulated 3.3V output over the entire life
of the battery. Extremely low operating current (typically 6µA
with no load) and low external parts count (one 0.1µF flying
capacitor and two small bypass capacitors at V
IN
and V
OUT
)
make the part ideally suited for small, light load battery-
powered applications. The total printed circuit board area of
the application circuit shown below is only 0.045in
2
.
The part operates as a Burst Mode
TM
switched-capacitor
voltage doubler to produce a regulated output. The part has
thermal shutdown capability and can survive a continuous
short circuit from V
OUT
to GND. The device is available in a
5-pin SOT-23 package.
, LTC and LT are registered trademarks of Linear Technology Corporation.
Burst Mode is a trademark of Linear Technology Corporation.
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Ultralow Power: I
CC
= 6
µ
A Typ
Short-Circuit/Thermal Protected
3.3V
±4%
Regulated Output
V
IN
Range: 2V to 4.4V
Output Current: 8mA (V
IN
≥
2V)
15mA (V
IN
≥
2.5V)
No Inductors
Ultrasmall Application Circuit (0.045in
2
)
700kHz Switching Frequency
Available in 5-Pin SOT-23
APPLICATIONS
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Cellular Telephones
Battery-Operated Equipment
Local Power Supplies
Handheld Instruments
PCMCIA Supplies
TYPICAL APPLICATION
Typical Output Voltage
vs Output Current
0.1µF
5
C1
–
LTC1517-3.3
V
IN
V
IN
2V TO 4.4V
3.3µF
1
GND
2
V
OUT
3
6.8µF
V
OUT
= 3.3V
±
4%
I
OUT
= 8mA (V
IN
≥
2V)
I
OUT
= 15mA (V
IN
≥
2.5V)
1517-3.3 TA01
3.40
T
A
= 25°C
C1 = 0.1µF
C
OUT
= 6.8µF
4
OUTPUT VOLTAGE (V)
C1
+
3.35
3.30
V
IN
= 2V
3.25
V
IN
= 2.5V
3.20
0
20
30
10
OUTPUT CURRENT (mA)
40
1517 G05
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LTC1517-3.3
ABSOLUTE
MAXIMUM
RATINGS
(Note 1)
PACKAGE/ORDER INFORMATION
TOP VIEW
V
IN
GND
V
OUT
1
2
3
4
C1
+
5
C1
–
V
IN
to GND ...................................................– 0.3V to 6V
V
OUT
to GND ................................................– 0.3V to 6V
V
OUT
Short-Circuit Duration ............................. Indefinite
Operating Temperature Range:
Commercial ............................................ 0°C to 70°C
Extended ............................................ – 40°C to 85°C
Storage Temperature Range ................. – 65°C to 150°C
Lead Temperature (Soldering, 10 sec).................. 300°C
ORDER PART
NUMBER
LTC1517CS5-3.3
LTC1517ES5-3.3
S5 PART MARKING
LTEF
LTTE
S5 PACKAGE
5-LEAD PLASTIC SOT-23
T
JMAX
= 125°C,
θ
JA
= 256°C/ W
Consult factory for Industrial and Military grade parts.
ELECTRICAL CHARACTERISTICS
V
IN
= 2V to 4.4V, C1 = 0.1µF, C
IN
= 3.3µF, C
OUT
= 6.8µF, T
MIN
to T
MAX
, unless otherwise noted.
SYMBOL
V
IN
V
OUT
I
CC
f
OSC
t
ON
I
SC
PARAMETER
Operating Input Voltage
Output Voltage
Input Supply Current
V
OUT
Ripple
Oscillator Frequency
V
OUT
Turn-On Time
Output Short-Circuit Current
V
IN
= 2.5V
V
IN
= 3V
2V
≤
V
IN
≤
4.4V, I
OUT
≤
8mA
2.5V
≤
V
IN
≤
4.4V, I
OUT
≤
15mA
2V
≤
V
IN
≤
4.4V, I
OUT
= 0
V
IN
= 2.5V, I
OUT
= 15mA, C
OUT
= 6.8µF
CONDITIONS
q
q
q
q
MIN
2.0
3.17
3.17
TYP
3.3
3.3
6
50
700
1
60
MAX
4.4
3.43
3.43
15
UNITS
V
V
V
µA
mV
P-P
kHz
ms
mA
The
q
denotes specifications that apply over the full operating
temperature range.
Note 1:
Absolute Maximum Ratings are those values beyond which the life
of the device may be impaired.
Note 2:
Extended grade parts are 100% tested at T
A
= 25°C. Performance
at – 40°C and 85°C is assured by design, characterization and correlation
with statistical process controls.
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LTC1517-3.3
TYPICAL PERFORMANCE CHARACTERISTICS
Output Voltage vs Input Voltage
3.40
I
OUT
= 8mA
C
OUT
= 6.8µF
OUTPUT VOLTAGE (V)
3.35
T
A
= 70°C
3.30
T
A
= 0°C
3.25
T
A
= 25°C
EFFICIENCY (%)
80
V
RIPPLE P-P
(mV)
100
I
OUT
= 8mA
T
A
= 25°C
150
3.20
2.0
2.5
3.5
4.0
3.0
INPUT VOLTAGE (V)
No Load Input Current vs
Input Voltage
10
I
OUT
= 0mA
8
T
A
= 70°C
6
T
A
= 0°C
4
T
A
= 25°C
EFFICIENCY (%)
INPUT CURRENT (µA)
2
2.0
2.5
3.5
4.0
3.0
INPUT VOLTAGE (V)
Typical Output Current
vs Temperature
50
V
OUT
SHORT-CIRCUIT CURRENT (mA)
V
OUT
= 3.3V
C1 = 0.1µF
40
OUTPUT CURRENT (mA)
30
V
IN
= 2.5V
20
V
IN
= 2V
10
0
–50
–25
0
25
50
TEMPERATURE (°C)
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1517 G01
1517 G04
Efficiency vs Input Voltage
200
Output Ripple vs Input Voltage
I
OUT
= 8mA
C1 = 0.1µF
C
IN
= 3.3µF
T
A
= 25°C
C
OUT
= 3.3µF
100
C
OUT
= 6.8µF
50
C
OUT
= 10µF
60
40
4.5
20
2.0
2.5
3.5
4.0
3.0
INPUT VOLTAGE (V)
4.5
1517 G02
0
2.0
2.5
3.5
4.0
3.0
INPUT VOLTAGE (V)
4.5
1517 G03
Typical Efficiency vs
Output Current
100
T
A
= 25°C
C1 = 0.1µF
C
OUT
= 6.8µF
V
IN
= 2V
V
IN
= 2.5V
60
V
OUT
AC COUPLED
50mV/DIV
I
OUT
0mA to 10mA
5mA/DIV
Load Transient Response
80
40
20
V
IN
= 2.5V
C
OUT
= 6.8µF
500µs/DIV
1517 G06
4.5
0
0.001
0.01
1
10
0.1
OUTPUT CURRENT (mA)
100
1517 TA02
V
OUT
Short-Circuit Current
vs Input Voltage
200
T
A
= 25°C
C1 = 0.1µF
160
V
IN
= 2.7V
120
80
40
75
100
1517 G09
0
2.0
2.5
3.5
4.0
3.0
INPUT VOLTAGE (V)
4.5
1517 G10
3
LTC1517-3.3
TYPICAL PERFORMANCE CHARACTERISTICS
Oscillator Frequency vs
Input Voltage
900
T
A
= 25°C
OSCILLATOR FREQUENCY (kHz)
900
V
IN
= 2.5V
OSCILLATOR FREQUENCY (kHz)
800
700
600
500
2.0
2.5
3.5
4.0
3.0
INPUT VOLTAGE (V)
PIN FUNCTIONS
V
IN
(Pin 1):
Charge Pump Input Voltage. May be between
2V and 4.4V. V
IN
should be bypassed with a
≥
3.3µF low
ESR capacitor as close as possible to the pin for best
performance.
GND (Pin 2):
Ground. Should be tied to a ground plane for
best performance.
V
OUT
(Pin 3):
Regulated Output Voltage. V
OUT
should be
bypassed with a
≥
3.3µF low ESR capacitor as close as
possible to the pin for best performance.
C1
+
(Pin 4):
Charge Pump Flying Capacitor Positive
Terminal.
C1
–
(Pin 5):
Charge Pump Flying Capacitor Negative
Terminal.
SI PLIFIED BLOCK DIAGRA
V
IN
C
IN
700kHz
OSC
4
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Oscillator Frequency vs
Temperature
800
700
600
500
4.5
1517 G07
400
–50
–25
0
25
50
TEMPERATURE (°C)
75
100
1517 G08
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C1
0.1µF
C1
–
C1
+
V
OUT
2.05M
C
OUT
CHARGE PUMP
+
–
THERMAL
SHDN
1.25V
REF
1.25M
1517-3.3 BD
LTC1517-3.3
APPLICATIONS INFORMATION
Operation
The LTC1517-3.3 uses a switched-capacitor charge pump
to boost V
IN
to a 3.3V
±4%
regulated output. The part
achieves regulation by sensing the output voltage through
an internal resistor divider and enabling the charge pump
when the divided output droops below the comparator’s
lower trip point (set by V
REF
). When the charge pump is
enabled, a 2-phase nonoverlapping clock controls the
internal charge pump switches. Flying capacitor C1 is
charged to V
IN
on phase one of the clock. On phase two of
the clock, C1 is stacked in series with V
IN
and connected
to V
OUT
through an internal switch. This sequence of
charging and discharging the flying capacitor occurs at a
free running frequency of 700kHz (typ) and continues until
the divided output voltage reaches the upper trip point of
the comparator. Once the output is back in regulation, the
charge pump is disabled. This method of bursting the
charge pump on and off enables the LTC1517-3.3 to
achieve high efficiency at extremely low output loads.
Capacitor Selection
For best performance, it is recommended that low ESR
capacitors be used for both C
IN
and C
OUT
to reduce noise
and ripple. The C
IN
and C
OUT
capacitors should be either
ceramic or tantalum and should be 3.3µF or greater.
Ceramic capacitors will provide the smallest size for a
given capacitance. If the input source impedance is very
low (< 0.5Ω), C
IN
may not be needed. Ceramic capacitors
are recommended for the flying capacitor C1 with values
of 0.1µF or 0.22µF. Smaller value flying capacitors may be
used in low I
OUT
applications.
Output Ripple
Normal LTC1517-3.3 operation produces voltage ripple
on the V
OUT
pin. Output voltage ripple is required for the
parts to regulate. Low frequency ripple exists due to the
hysteresis in the sense comparator and propagation de-
lays in the charge pump enable/disable circuits. High
frequency ripple is also present mainly from the ESR
(equivalent series resistance) in the output capacitor.
Typical output ripple with V
IN
= 2.5V under maximum load
is 75mV peak-to-peak with a low ESR 3.3µF output capaci-
tor (minimum recommended C
OUT
). For applications
requiring V
IN
to exceed 3.3V or for applications requiring
less than 75mV of peak-to-peak ripple, a 6.8µF to 10µF
C
OUT
capacitor is recommended. Slight further decreases
in output ripple can be achieved by using C
OUT
capacitors
larger than 10µF.
Short-Circuit/Thermal Protection
During short-circuit conditions, the LTC1517-3.3 will draw
between 20mA and 150mA from V
IN
, causing a rise in
junction temperature. On-chip thermal shutdown circuitry
disables the charge pump once the junction temperature
exceeds approximately 160°C. The charge pump is
reenabled once the junction temperature drops to approxi-
mately 145°C. The LTC1517-3.3 will cycle in and out of
thermal shutdown indefinitely without latchup or damage
until the V
OUT
short is removed.
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