LTC1514-3.3/LTC1514-5
Step-Up/Step-Down Switched
Capacitor DC/DC Converters
with Low-Battery Comparator
FEATURES
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DESCRIPTION
The LTC
®
1514-3.3/LTC1514-5 are micropower switched
capacitor DC/DC converters that produce a regulated
output voltage by either stepping up or stepping down
the input voltage. Output voltage is fixed at either 3.3V
(LTC1514-3.3) or 5V (LTC1514-5) by an internal resistor
divider.
A unique architecture allows the parts to accommodate
a wide input voltage range (2V to 10V) while maintaining
±4%
regulation. Additional circuitry prevents excessive
inrush current and output voltage ripple when large V
IN
to V
OUT
differentials are present.
An internal uncommitted comparator is kept active in
shutdown. The comparator has an open-drain output for
flexible interfacing.
The parts are short-circuit and overtemperature pro-
tected. Battery life is maximized by very low operating
currents (I
CC
= 60µA typ, 10µA in shutdown). Both parts
are available in an SO-8 package.
, LTC and LT are registered trademarks of Linear Technology Corporation.
3.3V or 5V Output Voltages
2V to 10V Input Voltage Range
Up to 50mA Output Current
Only Three External Capacitors Required
Soft Start Limits Inrush Current at Turn-On
Low Operating Current: 60µA
Low Shutdown Current: 10µA
Shutdown Disconnects Load from V
IN
Short-Circuit and Overtemperature Protected
650kHz Switching Frequency
Low-Battery Comparator Active in Shutdown
Available in SO-8 Package
APPLICATIONS
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Battery-Operated Equipment
Smart Card Readers
Local Power Supplies
Handheld Instruments
Battery Backup Supplies
TYPICAL APPLICATION
5V Step-Up/Step-Down Power Supply with Low-Battery Detect
5.2
100k
1.33M
1%
ON OFF
LOW BAT
1
2
3
499k
1%
4
LTC1514-5
SHDN
LBO
LBI
GND
V
OUT
V
IN
C1
+
C1
–
OUTPUT VOLTAGE (V)
8
7
6
5
0.22µF
V
OUT
= 5V
I
OUT
= 50mA
5.1
I
OUT
= 10mA
+
10µF
+
10µF
1514 TA01
V
IN
4-CELL
NiCd
5.0
4.9
4.8
U
2
U
U
LTC1514-5 Output Voltage
vs Input Voltage
3
4
5
8
6
7
INPUT VOLTAGE (V)
9
10
LT1514 • TA02
1
LTC1514-3.3/LTC1514-5
ABSOLUTE
MAXIMUM
RATINGS
(Note 1)
PACKAGE/ORDER INFORMATION
TOP VIEW
SHDN 1
LBO 2
LBI 3
GND 4
8 V
OUT
7 V
IN
6 C1
+
5 C1
–
V
IN
to GND ................................................ – 0.3V to 12V
V
OUT
to GND ............................................. – 0.3V to 12V
SHDN, LBI, LBO to GND ........................... – 0.3V to 12V
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
LTC1514CS8-3.3
LTC1514CS8-5
LTC1514IS8-3.3
LTC1514IS8-5
S8 PART MARKING
15143
15145
1514I3
1514I5
S8 PACKAGE
8-LEAD PLASTIC SO
T
JMAX
= 125°C,
θ
JA
= 110°C/ W
Consult factory for Military grade parts.
ELECTRICAL CHARACTERISTICS
V
IN
= 2V to 10V, SHDN = 3V, C1 = 0.22µF, C
IN
= C
OUT
= 10µF, unless otherwise noted (Note 2).
PARAMETER
V
IN
Operating Voltage
V
OUT
(LTC1514-3.3)
V
OUT
(LTC1514-5)
V
IN
Operating Current
V
IN
Shutdown Current
Output Ripple
Switching Frequency
LBI Trip Point
LBI Trip Point Hysteresis
LBI Input Current
LBO V
OL
LBO Leakage Current
SHDN Input Threshold
SHDN Input Current
I
OUT
Short-Circuit Current
t
ON
LBI = 1.145V
I
SINK
= 100µA, V
IN
= 3V
V
LBO
= 5V, LBI = V
IN
V
IL
V
IH
SHDN = V
IN
SHDN = 0V
V
OUT
= 0V
Soft Start Turn-On Time
Note 2:
For V
IN
≥
8V, C
OUT
= 22µF.
q
q
q
q
q
q
q
q
CONDITIONS
LTC1514-3.3
LTC1514-5
2V
≤
V
IN
≤
8V, I
OUT
≤
15mA
3V
≤
V
IN
≤
8V, I
OUT
≤
50mA
2.7V
≤
V
IN
≤
10V, I
OUT
≤
15mA
3.3V
≤
V
IN
≤
10V, I
OUT
≤
50mA
V
IN
≤
5V, I
OUT
= 0, SHDN = 3V
V
IN
> 5V, I
OUT
= 0, SHDN = 3V
SHDN = 0V, V
IN
≤
5V
SHDN = 0V, V
IN
> 5V
Full Load (Note 2)
q
q
q
q
q
q
q
q
q
q
MIN
2.0
2.7
3.17
3.17
4.8
4.8
TYP
MAX
8
10
UNITS
V
V
V
V
V
V
µA
µA
µA
µA
mV
P-P
kHz
V
%
nA
V
µA
V
V
µA
µA
mA
ms
3.3
3.3
5
5
60
75
10
100
3.43
3.43
5.2
5.2
100
120
20
35
800
1.180
50
500
1.110
– 50
650
1.145
1
0.025
LBI Ramping Negative
q
0.4
1
–1
0.4
–1
–1
12
4
1
1
1.6
1
1
40
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.
2
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LTC1514-3.3/LTC1514-5
TYPICAL PERFORMANCE CHARACTERISTICS
LTC1514-3.3
Efficiency vs Output Current
100
V
OUT
= 3.3V
T
A
= 25°C
80
V
IN
= 2V
V
IN
= 4.4V
100
OUTPUT VOLTAGE RIPPLE (mV
P-P
)
EFFICIENCY (%)
60
V
IN
= 2.7V
V
IN
= 6V
EFFICIENCY (%)
40
20
0
0.01
0.1
1
10
OUTPUT CURRENT (mA)
LTC1514-5 Output Voltage Ripple
vs Input Voltage
250
3.45
V
OUT
= 5V
I
OUT
= 10mA
T
A
= 25°C
C
OUT
= 10µF
150
C
OUT
= 22µF
100
C
OUT
= 47µF
OUTPUT VOLTAGE RIPPLE (mV
P-P
)
3.35
OPERATING CURRENT (µA)
200
OUTPUT VOLTAGE (V)
50
0
0
2
6
4
INPUT VOLTAGE (V)
8
10
1514 G04
LTC1514-3.3
Efficiency vs Input Voltage
100
V
OUT
= 3.3V
I
OUT
= 10mA
T
A
= 25°C
SHUTDOWN SUPPLY CURRENT (µA)
80
EFFICIENCY (%)
EFFICIENCY (%)
60
40
20
0
2
6
4
INPUT VOLTAGE (V)
U W
100
1514 G01
LTC1514-5
Efficiency vs Output Current
250
V
IN
= 2.7V
80
V
IN
= 3.3V
60
V
IN
= 8V
V
IN
= 6V
LTC1514-3.3 Output Voltage
Ripple vs Input Voltage
V
OUT
= 3.3V
I
OUT
= 10mA
T
A
= 25°C
200
150
C
OUT
= 10µF
100
C
OUT
= 22µF
40
20
V
OUT
= 5V
T
A
= 25°C
0
0.01
0.1
1
10
OUTPUT CURRENT (mA)
100
1514 G02
50
C
OUT
= 47µF
0
0
2
6
4
INPUT VOLTAGE (V)
8
10
1514 G03
LTC1514-3.3 Output Voltage
vs Input Voltage
120
V
OUT
= 3.3V
C
OUT
= 10µF
T
A
= 25°C
LTC1514-5 Operating Current
vs Input Voltage
V
OUT
= 5V
I
OUT
= 0mA
100
3.40
80
25°C
60
85°C
–40°C
3.30
3.25
40
3.20
0
2
6
4
INPUT VOLTAGE (V)
8
10
1514 G05
20
0
2
6
4
INPUT VOLTAGE (V)
8
10
1514 G06
LTC1514-5
Efficiency vs Input Voltage
100
V
OUT
= 5V
I
OUT
= 10mA
T
A
= 25°C
25
LTC1514-X Shutdown Supply
Current vs Input Voltage
SHDN = 0V
20
80
15
25°C
10
–40°C
5
85°C
60
40
8
10
1514 G07
20
0
2
4
8
6
INPUT VOLTAGE (V)
10
12
1514 G08
0
2
6
4
INPUT VOLTAGE (V)
8
10
1514 G09
3
LTC1514-3.3/LTC1514-5
TYPICAL PERFORMANCE CHARACTERISTICS
LTC1514-5 Step-Down Mode
Load Transient Response
LTC1514-5 Step-Up Mode
Load Transient Response
V
OUT
AC COUPLED
100mV/DIV
I
OUT
50mA/DIV
V
IN
= 8V, V
OUT
= 5V, C
OUT
= 10µF, T
A
= 25°C
1514 G10
BLOCK DIAGRAM
V
IN
SHDN
LBO
PIN FUNCTIONS
SHDN (Pin 1):
Shutdown Input. A logic low on the SHDN
pin puts the part into shutdown mode. A logic high
(V
SHDN
≥
1.6V) enables the charge pump regulator. At
high V
IN
voltages, the SHDN pin may still be controlled
with 3V logic without causing a large rise in V
IN
quiescent
current. The SHDN pin may not float; connect to V
IN
if
unused.
LBO (Pin 2):
Open-Drain, Low-Battery Comparator Out-
put. This pin will pull low whenever the voltage on the LBI
pin is less than the internal reference voltage (1.145V typ).
LBI (Pin 3):
Low-Battery Comparator Input. The voltage
on this pin is compared to the internal reference voltage
(1.145V). The LBO output will sink current when the
voltage on the LBI pin is less than 1.145V typ. The low-
4
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V
OUT
AC COUPLED
100mV/DIV
50mA
0mA
I
OUT
50mA/DIV
V
IN
= 3.3V, V
OUT
= 5V, C
OUT
= 10µF, T
A
= 25°C
1514 G11
W
C1
–
C1
+
STEP-UP/STEP-DOWN
CHARGE PUMP
V
OUT
–
650kHz
OSCILLATOR
+
–
+
1.145V
V
REF
LBI
GND
1514 BD
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U
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LTC1514-3.3/LTC1514-5
PIN FUNCTIONS
battery comparator and 1.145V reference are kept alive in
shutdown.
GND (Pin 4):
Ground. Should be tied to a ground plane for
best performance.
C1
–
(Pin 5):
Charge Pump Flying Capacitor, Negative
Terminal.
C1
+
(Pin 6):
Charge Pump Flying Capacitor, Positive
Terminal.
V
IN
(Pin 7):
Charge Pump Input Voltage. May be between
2V and 8V (LTC1514-3.3) or between 2.7V and 10V
(LTC1514-5). V
IN
should be bypassed with a
≥
10µF low
ESR capacitor as close as possible to the pin for best
performance.
V
OUT
(Pin 8):
Regulated Output Voltage. The output volt-
age is internally set to either 3.3V (LTC1514-3.3) or to 5V
(LTC1514-5) using an internal resistor divider. V
OUT
should
be bypassed with a
≥
10µF low ESR capacitor as close as
possible to the pin for best performance.
APPLICATIONS INFORMATION
Regulator Operation
The regulator section of the LTC1514-3.3/LTC1514-5
consists of a charge pump, reference, comparator and
some logic. The divided down output voltage is com-
pared to the internal reference voltage. When the divided
output drops below the reference voltage, the charge
pump is enabled, which boosts the output back into
regulation. Hysteresis in the comparator forces the regu-
lator to burst on and off and causes approximately
100mV of peak-to-peak ripple to appear at the output. By
enabling the charge pump only when needed, the
LTC1514-3.3 and LTC1514-5 are able to achieve high
efficiencies with low output load currents.
Each part’s charge pump has a unique architecture that
allows the input voltage to be either stepped up or
stepped down to produce a regulated output. Internal
circuitry senses the V
IN
to V
OUT
differential voltage and
controls the charge pump operating mode. In addition,
the effective output impedance of the charge pump is
internally adjusted to prevent large inrush currents and
allow for a wide input voltage range. When the input
voltage is lower than the output voltage, the charge pump
operates as a step-up voltage doubler. When the input
voltage is greater than the output, the charge pump
operates as a step-down gated switch.
Capacitor Selection
For best performance, low ESR capacitors are recom-
mended 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 (< 0.5Ω), C
IN
may not be
needed. Increasing the size of C
OUT
to 22µF or greater will
reduce output voltage ripple—particularly with high V
IN
voltages (8V or greater). A ceramic capacitor is recom-
mended for the flying capacitor C1 with a value of 0.1µF
or 0.22µF. Smaller value flying capacitors may be used in
low output current applications.
Output Ripple
Normal LTC1514-3.3/LTC1514-5 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 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 (V
IN
< 8V) under maxi-
mum load is 100mV peak-to-peak with a low ESR (< 0.5Ω)
10µF output capacitor. For applications requiring V
IN
to
exceed 8V, a 22µF or larger C
OUT
capacitor is recom-
mended to maintain max ripple in the 100mV range.
The magnitude of the ripple voltage depends on several
factors. High input voltages increase the output ripple
since more charge is delivered to C
OUT
per charging
cycle. A large C1 flying capacitor (> 0.22µF) also
increases ripple in step-up mode for the same reason.
Large output current load and/or a small output capacitor
(< 10µF) results in higher ripple due to higher output
voltage dV/dt. High ESR capacitors (ESR > 0.5Ω) on the
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