LTC1517-5
Micropower, Regulated
5V Charge Pump in a
5-Pin SOT-23 Package
FEATURES
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DESCRIPTION
The LTC
®
1517-5 is a micropower charge pump DC/DC
converter that produces a regulated 5V output. The input
voltage range is 2.7V to 5V. 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
5V
±4%
Regulated Output
V
IN
Range: 2.7V to 5V
Output Current: 10mA (V
IN
≥
2.7V)
20mA (V
IN
≥
3V)
No Inductors
Ultrasmall Application Circuit (0.045in
2
)
800kHz 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
5.2
0.1µF
5
C1
–
LTC1517-5
V
IN
V
IN
2.7V TO 5V
3.3µF
1
GND
2
V
OUT
3
6.8µF
V
OUT
= 5V
±
4%
I
OUT
= 10mA (V
IN
≥
2.7V)
I
OUT
= 20mA (V
IN
≥
3V)
1517 TA01
C1
+
OUTPUT VOLTAGE (V)
4
5.1
T
A
= 25°C
C1 = 0.1µF
C
OUT
= 6.8µF
5.0
4.9
V
IN
= 2.7V V
IN
= 3V V
IN
= 3.3V
4.8
0
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40
60
20
OUTPUT CURRENT (mA)
80
1517 TA02
1
LTC1517-5
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 (Note 2).............................. – 40°C to 85°C
Storage Temperature Range ................. – 65°C to 150°C
Lead Temperature (Soldering, 10 sec).................. 300°C
ORDER PART
NUMBER
LTC1517CS5-5
LTC1517ES5-5
S5 PART MARKING
LTCX
LTTF
S5 PACKAGE
5-LEAD PLASTIC SOT-23
T
JMAX
= 125°C,
θ
JA
= 256°C/ W
Consult factory for Industrial and Military grade parts and for -3 and -3.3
version availability.
ELECTRICAL CHARACTERISTICS
V
IN
= 2.7V to 5V, 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
PARAMETER
Operating Input Voltage
Output Voltage
Input Supply Current
V
OUT
Ripple
Oscillator Frequency
V
OUT
Turn-On Time
V
IN
= 3V
2.7V
≤
V
IN
≤
5V, I
OUT
≤
10mA
3V
≤
V
IN
≤
5V, I
OUT
≤
20mA
2.7V
≤
V
IN
≤
5V, I
OUT
= 0
V
IN
= 3V, I
OUT
= 20mA, C
OUT
= 6.8µF
CONDITIONS
q
q
q
q
MIN
2.7
4.8
4.8
TYP
5.0
5.0
6
75
800
1
MAX
5
5.2
5.2
15
UNITS
V
V
V
µA
mV
P-P
kHz
ms
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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LTC1517-5
TYPICAL PERFORMANCE CHARACTERISTICS
Output Voltage vs Input Voltage
5.15
I
OUT
= 10mA
C
OUT
= 10µF
5.10
OUTPUT VOLTAGE (V)
EFFICIENCY (%)
V
RIPPLE P-P
(mV)
5.05
T
A
= 70°C
5.00
T
A
= 25°C
4.95
T
A
= 0°C
4.90
2.5
3.0
4.0
4.5
3.5
INPUT VOLTAGE (V)
No Load Input Current
vs Input Voltage
9
I
OUT
= 0mA
8
INPUT CURRENT (µA)
80
90
7
T
A
= 25°C
EFFICIENCY (%)
T
A
= 70°C
6
T
A
= 0°C
5
V
IN
= 3V
C
OUT
= 6.8µF
500µs/DIV
1517-5 G06
4
2.5
3.0
4.0
4.5
3.5
INPUT VOLTAGE (V)
U W
1517-5 G01
1517-5 G04
Efficiency vs Input Voltage
90
I
OUT
= 10mA
T
A
= 25°C
80
200
250
Output Ripple vs Input Voltage
I
OUT
= 10mA
C1 = 0.1µF
T
A
= 25°C
C
OUT
= 3.3µF
150
C
OUT
= 6.8µF
100
C
OUT
= 10µF
50
C
OUT
= 22µF
70
60
50
5.0
40
2.5
3.0
4.0
4.5
3.5
INPUT VOLTAGE (V)
5.0
1517-5 G02
0
2.5
3.0
4.0
4.5
3.5
INPUT VOLTAGE (V)
5.0
1517-5 G03
Efficiency vs Output Current
V
IN
= 3V
SHDN = 0V
T
A
= 25°C
Load Transient Response
I
OUT
0mA to 10mA
10mA/DIV
70
V
OUT
AC COUPLED
50mV/DIV
60
5.0
50
0.01
0.1
1
10
OUTPUT CURRENT (mA)
100
1517-5 G05
3
LTC1517-5
PIN FUNCTIONS
V
IN
(Pin 1):
Charge Pump Input Voltage. May be between
2.7V and 5V. 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
C1
–
CHARGE PUMP
3.75M
800kHz
OSC
LTC1517-5
1517 BD
4
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C1
0.1µF
C1
+
V
OUT
C
OUT
+
–
THERMAL
SHDN
1.25V
REF
1.25M
LTC1517-5
APPLICATIONS INFORMATION
Operation
The LTC1517-5 uses a switched-capacitor charge pump
to boost V
IN
to a 5V
±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 800kHz (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 LTC1517-5 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 and
lowest ESR 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 ca-
pacitor C1 with values of 0.1µF or 0.22µF. Smaller value
flying capacitors may be used in low I
OUT
applications.
Output Ripple
Normal LTC1517-5 operation produces voltage ripple on
the V
OUT
pin. Output voltage ripple is required for the part
to regulate. Low frequency ripple exists due to the hyster-
esis in the sense comparator and propagation delays 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
= 3V under maximum load is 100mV peak-to-peak
with a low ESR (< 0.5Ω) 3.3µF output capacitor (minimum
recommended C
OUT
). For applications requiring V
IN
to
exceed 3.3V or for applications requiring < 100mV 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 LTC1517-5 will draw
between 50mA and 200mA 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 LTC1517-5 will cycle in and out of
thermal shutdown indefinitely without latchup or damage
until the V
OUT
short is removed.
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