LTC1516
Micropower, Regulated
5V Charge Pump
DC/DC Converter
FEATURES
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DESCRIPTION
The LTC
®
1516 is a micropower charge pump DC/DC
converter that produces a regulated 5V output from a 2V
to 5V supply. Extremely low supply current (12µA typical
with no load, < 1µA in shutdown) and low external parts
count (two 0.22µF flying capacitors and two 10µF capaci-
tors at V
IN
and V
OUT
) make the LTC1516 ideally suited for
small, light load battery-powered applications. Typical
efficiency (V
IN
= 3V) exceeds 70% with load currents
between 50µA and 50mA. Modulating the SHDN pin keeps
the typical efficiency above 70% with load currents all the
way down to 10µA.
The LTC1516 operates as either a doubler or a tripler
depending on V
IN
and output load conditions to improve
overall efficiency. The part has thermal shutdown and can
survive a continuous short from V
OUT
to GND. In shut-
down the load is disconnected from V
IN
.
The LTC1516 is available in an 8-pin SO package in both
commercial and industrial temperature grades.
, LTC and LT are registered trademarks of Linear Technology Corporation.
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Ultralow Power: Typical Operating I
CC
= 12µA
Short Circuit/Thermal Protection
Regulated 5V
±4%
Output
2V to 5V Input Range
No Inductors
I
CC
in Shutdown: < 1µA
Output Current: 20mA (V
IN
> 2V)
50mA (V
IN
> 3V)
Shutdown Disconnects Load from V
IN
Internal Oscillator: 600kHz
Compact Application Circuit (0.1 in
2
)
8-Pin SO Package
APPLICATIONS
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2-Cell to 5V Conversion
Li-Ion Battery Backup Supplies
Local 3V to 5V Conversion
5V Flash Memory Programmer
Smart Card Readers
TYPICAL APPLICATION
0.22µF
Efficiency vs Output Current
90
V
IN
= 3V
1
2
C1
+
V
IN
V
OUT
C2
+
0.22µF
C1
–
SHDN
LTC1516
GND
C2
–
8
80
+
10µF
3
10µF 4
EFFICIENCY (%)
V
IN
= 2V TO 5V
7
6
5
ON/OFF
70
+
SHDN = 0V
60
V
OUT
= 5V
±4%
I
OUT
= 0mA TO 20mA, V
IN
≥
2V
I
OUT
= 0mA TO 50mA, V
IN
≥
3V
50
0.01
1516 • F01
Figure 1. Regulated 5V Output from a 2V to 5V Input
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LOW I
Q
MODE
(SEE FIGURE 3)
0.1
1
10
OUTPUT CURRENT (mA)
100
1516 • TA01
1
LTC1516
ABSOLUTE
MAXIMUM
RATINGS
(Note 1)
PACKAGE/ORDER INFORMATION
TOP VIEW
C1
+
1
V
IN
2
V
OUT
3
C2
+
4
8 C1
–
7 SHDN
6 GND
5 C2
–
V
IN
to GND ...................................................– 0.3V to 6V
V
OUT
to GND ................................................– 0.3V to 6V
SHDN to GND ..............................................– 0.3V to 6V
V
OUT
Short-Circuit Duration ............................. Indefinite
Operating Temperature Range
Commercial ............................................. 0°C to 70°C
Industrial ............................................ – 40°C to 85°C
Storage Temperature Range ................. – 65°C to 150°C
Lead Temperature (Soldering, 10 sec).................. 300°C
ORDER PART
NUMBER
LTC1516CS8
LTC1516IS8
S8 PART MARKING
1516
1516I
S8 PACKAGE
8-LEAD PLASTIC SO
T
JMAX
= 125°C,
θ
JA
= 150°C/ W
Consult factory for Military grade parts.
ELECTRICAL CHARACTERISTICS
SYMBOL PARAMETER
V
IN
Input Voltage
V
OUT
Output Voltage
CONDITIONS
V
IN
= 2V to 5V, C1 = C2 = 0.22µF, C
IN
= C
OUT
= 10µF, T
MIN
to T
MAX
unless otherwise specified (Note 3).
q
I
CC
Supply Current
Output Ripple
Efficiency
Switching Frequency
SHDN Input Threshold
SHDN Input Current
V
OUT
Turn-On Time
f
OSC
V
IH
V
IL
I
IH
I
IL
t
ON
2V
≤
V
IN
≤
5V, I
OUT
≤
20mA
3V
≤
V
IN
≤
3.6V, I
OUT
≤
50mA
3.6V
≤
V
IN
≤
5V, I
OUT
≤
50mA, T
A
= 25°C (Note 2)
2V
≤
V
IN
≤
5V, I
OUT
= 0mA, SHDN = 0V
2V
≤
V
IN
≤
5V, I
OUT
= 0mA, SHDN = V
IN
Full Load
V
IN
= 3V, I
OUT
= 20mA
Full Load
q
q
q
q
MIN
2
4.8
4.8
4.8
TYP
12
0.005
100
82
600
(0.7)(V
IN
)
–1
–1
500
MAX
5
5.2
5.2
5.2
20
1
q
q
V
SHDN
= V
IN
V
SHDN
= 0V
V
IN
= 3V, I
OUT
= 0mA (Note 3)
q
q
0.4
1
1
UNITS
V
V
V
V
µA
µA
mV
%
kHz
V
V
µA
µA
µs
The
q
denotes specifications which 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:
At input voltages > 3.6V and ambient temperatures >70°C,
continuous power dissipation must be derated to maintain junction
temperatures below 125°C. Derate 6mW/°C above 70°C in SO-8.
Note 3:
The LTC1516 is tested with the capacitors shown in Figure 1.
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LTC1516
TYPICAL PERFORMANCE CHARACTERISTICS
Efficiency vs Input Voltage
90
I
OUT
= 10mA
MAXIMUM OUTPUT CURRENT (mA)
EFFICIENCY (%)
80
60
40
20
0
C1 = C2
= 0.1µF
C1 = C2
= 0.047µF
C1 = C2
= 0.022µF
C1 = C2 = 0.01µF
SUPPLY CURRENT (µA)
80
70
60
50
2.0
2.5
3.0
3.5
4.0
INPUT VOLTAGE (V)
4.5
5.0
Output Voltage vs Input Voltage
5.10
I
OUT
= 20mA
5.05
5.05
5.10
OUTPUT VOLTAGE (V)
OUTPUT VOLTAGE (V)
5.00
4.95
4.90
1
2
3
4
INPUT VOLTAGE (V)
5
6
1516 • G04
PIN FUNCTIONS
C1
+
(Pin 1):
Flying Capacitor 1, Positive Terminal.
V
IN
(Pin 2):
Input Supply Voltage.
V
OUT
(Pin 3):
5V Output Voltage (V
OUT
= 0V in Shutdown).
C2
+
(Pin 4):
Flying Capacitor 2, Positive Terminal.
C2
–
(Pin 5):
Flying Capacitor 2, Negative Terminal.
GND (Pin 6):
Ground.
SHDN (Pin 7):
Active High CMOS Logic-Level Shutdown
Input.
C1
–
(Pin 8):
Flying Capacitor 1, Negative Terminal.
U W
1516 • G01
Output Current vs Input Voltage
120
C
OUT
= 10µF
T
A
= 25°C
100
C1 = C2
= 0.22µF
No Load Supply Current vs
Input Voltage
20
15
10
5
5
2
3
4
INPUT VOLTAGE (V)
2
3
4
INPUT VOLTAGE (V)
5
1516 • G03
1516 • G02
Output Voltage vs Output Current
V
IN
= 3V
Load Transient Response, V
IN
= 3V
I
OUT
,
0mA TO 25mA,
10mA/DIV
5.00
V
OUT
,
AC COUPLED,
100mV/DIV
4.95
1516 • G04
4.90
0.01
0.1
1
10
OUTPUT CURRENT (mA)
100
1516 • G05
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LTC1516
BLOCK DIAGRAM
V
IN
10µF
+
S2A
S1A
S2B
C2
–
COMP1
S1B
CLOCK 1
COMP2
C1
+
S1C
S2C
C1
–
S1D
S3
V
REF
CHARGE PUMP
CLOCK 2
COMP3
V
OS
CONTROL
LOGIC
C2
+
0.22µF
0.22µF
CHARGE PUMP SHOWN IN TRIPLER MODE, DISCHARGE CYCLE
APPLICATIONS INFORMATION
Operation
The LTC1516 uses a switched capacitor charge pump to
boost V
IN
from 2V to 5V to a regulated 5V
±4%
output
voltage. Regulation is achieved by sensing the output
voltage through an internal resistor divider and enabling
the charge pump when the output voltage droops below
the lower trip point of COMP2. When the charge pump is
enabled, a 2-phase, nonoverlapping clock controls the
charge pump switches. Clock 1 closes the S1 switches
which enable the flying capacitors, C1 and C2, to charge
up to the V
IN
voltage. Clock 2 closes the S2 switches which
stack C1 and C2 in series with V
IN
and connect the top
plate of C2 to the output capacitor at V
OUT
. This sequence
of charging and discharging continues at a free-running
frequency of 600kHz (typ) until the output has risen to the
upper trip point of COMP2 and the charge pump is
disabled. When the charge pump is disabled, the LTC1516
draws only 8µA (typ) from V
IN
which provides high
efficiency at low load conditions.
To achieve the highest efficiency over the entire V
IN
range,
the LTC1516 operates as either a doubler or a tripler
depending on V
IN
and output load conditions. COMP1 and
COMP2 determine whether the charge pump is in doubler
mode or tripler mode. COMP1 forces the part into tripler
mode if V
IN
is < 2.55V, regardless of output load. When V
IN
is > 2.55V, the part will be in doubler mode using only C2
as a flying capacitor. In doubler mode, if the output droops
by 50mV under heavy loads, COMP3 will force the charge
pump into tripler mode until V
OUT
climbs above the upper
trip point of COMP3. Under these V
IN
and load conditions,
the nominal V
OUT
will be approximately 50mV lower than
the no load nominal V
OUT
. This method of sensing V
IN
and
output load results in efficiency greater than 80% with V
IN
between 2.5V and 3V.
In shutdown mode, all circuitry is turned off and the part
draws only leakage current (< 1µA) from the V
IN
supply.
V
OUT
is also disconnected from V
IN
. The SHDN pin is a
CMOS input with a threshold of approximately V
IN
/2;
however, the SHDN pin can be driven by logic levels that
exceed the V
IN
voltage. The part enters shutdown mode
when a logic high is applied to the SHDN pin. The SHDN pin
cannot float; it must be driven with a logic high or low.
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SHDN
V
OUT
+
10µF
LTC1516 • BD
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LTC1516
APPLICATIONS INFORMATION
Short-Circuit/Thermal Protection
During short-circuit conditions, the LTC1516 will draw
between 200mA and 400mA from V
IN
causing a rise in
the junction temperature. On-chip thermal shutdown
circuitry disables the charge pump once the junction
temperature exceeds 135°C, and reenables the charge
pump once the junction temperature falls back to 115°C.
The LTC1516 will cycle in and out of thermal shutdown
indefinitely without latchup or damage until the V
OUT
short
is removed.
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 10µF or greater. If the
input source impedance is very low, C
IN
may not be
needed. Increasing the size of C
OUT
to 22µF or greater will
reduce output voltage ripple.
Ceramic or tantalum capacitors are recommended for the
flying caps C1 and C2 with values in the range of 0.1µF to
1µF. Note that large value flying caps (> 0.22µF) will
increase output ripple unless C
OUT
is also increased. For
very low load applications, C1 and C2 may be reduced to
0.01µF to 0.047µF. This will reduce output ripple at the
expense of efficiency and maximum output current.
Output Ripple
Normal LTC1516 operation produces voltage ripple on the
V
OUT
pin. Output voltage ripple is required for the LTC1516
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 due to ESR (Equivalent Series
Resistance) in the output capacitor. Typical output ripple
under maximum load is 100mV
P-P
with a low ESR 10µF
output capacitor.
The magnitude of the ripple voltage depends on several
factors. High input voltages (V
IN
> 3.3V) increase the output
ripple since more charge is delivered to C
OUT
per clock
cycle. Large C1 and C2 flying capacitors (> 0.22µF) also
increase ripple for the same reason. Large output current
load and/or a small output capacitor (< 10µF) results in
LTC1516
3
V
OUT
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higher ripple due to higher output voltage dV/dt. High ESR
capacitors (ESR > 0.5Ω) on the output pin cause high
frequency voltage spikes on V
OUT
with every clock cycle.
There are several ways to reduce the output voltage ripple.
A larger C
OUT
capacitor (22µF or greater) will reduce both
the low and high frequency ripple due to the lower C
OUT
charging and discharging dV/dt and the lower ESR typi-
cally found with higher value (larger case size) capacitors.
A low ESR ceramic output capacitor will minimize the high
frequency ripple, but will not reduce the low frequency
ripple unless a high capacitance value is chosen. A reason-
able compromise is to use a 10µF to 22µF tantalum
capacitor in parallel with a 1µF to 3.3µF ceramic capacitor
on V
OUT
to reduce both the low and high frequency ripple.
An RC filter may also be used to reduce high frequency
voltage spikes (see Figure 2).
In low load or high V
IN
applications, smaller values for C1
and C2 may be used to reduce output ripple. The smaller
C1 and C2 flying capacitors (0.022µF to 0.1µF) deliver less
charge per clock cycle to the output capacitor resulting in
lower output ripple. However, the smaller value flying caps
also reduce the maximum I
OUT
capability as well as
efficiency.
LTC1516
3
V
OUT
+
15µF
TANTALUM
1µF
CERAMIC
V
OUT
5V
2Ω
+
10µF
+
10µF
V
OUT
5V
1516 F02
Figure 2. Output Ripple Reduction Techniques
Inrush Currents
During normal operation, V
IN
will experience current tran-
sients in the 100mA to 200mA range whenever the charge
pump is enabled. During start-up, these inrush currents
may approach 500mA. For this reason, it is important to
minimize the source resistance between the input supply
and the V
IN
pin to prevent start-up problems and large
input voltage transients.
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