1
LTC1516
Micropower, Regulated
5V Charge Pump
DC/DC Converter
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 (12
A typical
with no load, < 1
A in shutdown) and low external parts
count (two 0.22
F flying capacitors and two 10
F 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 50
A and 50mA. Modulating the SHDN pin keeps
the typical efficiency above 70% with load currents all the
way down to 10
A.
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.
s
Ultralow Power: Typical Operating I
CC
= 12
A
s
Short Circuit/Thermal Protection
s
Regulated 5V
4% Output
s
2V to 5V Input Range
s
No Inductors
s
I
CC
in Shutdown: < 1
A
s
Output Current: 20mA (V
IN
> 2V)
50mA (V
IN
> 3V)
s
Shutdown Disconnects Load from V
IN
s
Internal Oscillator: 600kHz
s
Compact Application Circuit (0.1 in
2
)
s
8-Pin SO Package
FEATURES
DESCRIPTIO
N
U
, LTC and LT are registered trademarks of Linear Technology Corporation.
Figure 1. Regulated 5V Output from a 2V to 5V Input
Efficiency vs Output Current
APPLICATIO
N
S
U
s
2-Cell to 5V Conversion
s
Li-Ion Battery Backup Supplies
s
Local 3V to 5V Conversion
s
5V Flash Memory Programmer
s
Smart Card Readers
TYPICAL APPLICATIO
N
U
1
2
3
4
8
7
6
5
C1
SHDN
GND
C2
C1
+
V
IN
V
OUT
C2
+
LTC1516
0.22
F
ON/OFF
10
F
10
F
V
OUT
= 5V
4%
I
OUT
= 0mA TO 20mA, V
IN
2V
I
OUT
= 0mA TO 50mA, V
IN
3V
0.22
F
V
IN
= 2V TO 5V
+
+
1516 F01
OUTPUT CURRENT (mA)
50
60
70
80
90
EFFICIENCY (%)
100
1516 TA01
0.01
0.1
1
10
SHDN = 0V
V
IN
= 3V
LOW I
Q
MODE
(SEE FIGURE 3)
2
LTC1516
ABSOLUTE
M
AXI
M
U
M
RATINGS
W
W
W
U
PACKAGE/ORDER I
N
FOR
M
ATIO
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(Note 1)
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
ELECTRICAL CHARACTERISTICS
V
IN
= 2V to 5V, C1 = C2 = 0.22
F, C
IN
= C
OUT
= 10
F, T
MIN
to T
MAX
unless otherwise specified (Note 3).
SYMBOL PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
V
IN
Input Voltage
q
2
5
V
V
OUT
Output Voltage
2V
V
IN
5V, I
OUT
20mA
q
4.8
5.2
V
3V
V
IN
3.6V, I
OUT
50mA
q
4.8
5.2
V
3.6V
V
IN
5V, I
OUT
50mA, T
A
= 25
C (Note 2)
4.8
5.2
V
I
CC
Supply Current
2V
V
IN
5V, I
OUT
= 0mA, SHDN = 0V
q
12
20
A
2V
V
IN
5V, I
OUT
= 0mA, SHDN = V
IN
q
0.005
1
A
Output Ripple
Full Load
100
mV
Efficiency
V
IN
= 3V, I
OUT
= 20mA
82
%
f
OSC
Switching Frequency
Full Load
600
kHz
V
IH
SHDN Input Threshold
q
(0.7)(V
IN
)
V
V
IL
q
0.4
V
I
IH
SHDN Input Current
V
SHDN
= V
IN
q
1
1
A
I
IL
V
SHDN
= 0V
q
1
1
A
t
ON
V
OUT
Turn-On Time
V
IN
= 3V, I
OUT
= 0mA (Note 3)
500
s
S8 PART MARKING
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.
1516
1516I
ORDER PART
NUMBER
LTC1516CS8
LTC1516IS8
T
JMAX
= 125
C,
JA
= 150
C/ W
1
2
3
4
8
7
6
5
TOP VIEW
C1
SHDN
GND
C2
C1
+
V
IN
V
OUT
C2
+
S8 PACKAGE
8-LEAD PLASTIC SO
Consult factory for Military grade parts.
3
LTC1516
TYPICAL PERFOR
M
A
N
CE CHARACTERISTICS
U
W
Output Voltage vs Input Voltage
Efficiency vs Input Voltage
No Load Supply Current vs
Input Voltage
Output Current vs Input Voltage
INPUT VOLTAGE (V)
50
60
70
80
90
EFFICIENCY (%)
5.0
1516 G01
2.0
2.5
3.0
4.0
4.5
3.5
I
OUT
= 10mA
INPUT VOLTAGE (V)
0
40
20
100
120
80
60
MAXIMUM OUTPUT CURRENT (mA)
5
1516 G02
2
3
4
C1 = C2
= 0.22
F
C1 = C2
= 0.047
F
C1 = C2
= 0.022
F
C1 = C2
= 0.1
F
C1 = C2 = 0.01
F
C
OUT
= 10
F
T
A
= 25
C
INPUT VOLTAGE (V)
5
10
15
20
SUPPLY CURRENT (
A)
5
1516 G03
2
3
4
INPUT VOLTAGE (V)
I
OUT
= 20mA
4.90
4.95
5.05
5.00
5.10
OUTPUT VOLTAGE (V)
6
5
1516 G04
2
1
3
4
OUTPUT CURRENT (mA)
4.90
5.10
5.05
5.00
4.95
OUTPUT VOLTAGE (V)
1516 G05
0.01
0.1
1
10
100
V
IN
= 3V
Output Voltage vs Output Current
I
OUT
,
0mA TO 25mA,
10mA/DIV
V
OUT
,
AC COUPLED,
100mV/DIV
1516 G04
Load Transient Response, V
IN
= 3V
PI
N
FU
N
CTIO
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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.
4
LTC1516
BLOCK DIAGRA
M
W
COMP1
COMP2
COMP3
V
REF
CLOCK 1
CLOCK 2
CONTROL
LOGIC
V
OS
S3
S2A
S2B
S2C
S1A
S1B
S1C
S1D
0.22
F
10
F
0.22
F
C1
+
C1
C2
+
C2
10
F
V
OUT
SHDN
LTC1516 BD
CHARGE PUMP SHOWN IN TRIPLER MODE, DISCHARGE CYCLE
V
IN
CHARGE PUMP
+
+
APPLICATIO
N
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FOR
M
ATIO
N
W
U
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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 8
A (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 (< 1
A) 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.
5
LTC1516
APPLICATIO
N
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FOR
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higher ripple due to higher output voltage dV/dt. High ESR
capacitors (ESR > 0.5
) 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 (22
F 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 10
F to 22
F tantalum
capacitor in parallel with a 1
F to 3.3
F 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 (0.022
F to 0.1
F) 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.
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 10
F or greater. If the
input source impedance is very low, C
IN
may not be
needed. Increasing the size of C
OUT
to 22
F 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 0.1
F to
1
F. Note that large value flying caps (> 0.22
F) will
increase output ripple unless C
OUT
is also increased. For
very low load applications, C1 and C2 may be reduced to
0.01
F to 0.047
F. 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 10
F
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 (> 0.22
F) also
increase ripple for the same reason. Large output current
load and/or a small output capacitor (< 10
F) results in
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.
V
OUT
5V
LTC1516
3
15
F
TANTALUM
1
F
CERAMIC
V
OUT
5V
V
OUT
+
LTC1516
3
1516 F02
2
10
F
V
OUT
+
10
F
+
Figure 2. Output Ripple Reduction Techniques
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