LTC1515 Series
Step-Up/Step-Down
Switched Capacitor DC/DC
Converters with Reset
FEATURES
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DESCRIPTION
The LTC
®
1515, LTC1515-3/5 and LTC1515-3.3/5 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
adjustable using an external resistor divider (LTC1515) or
programmable to either 3V/5V (LTC1515-3/5) or 3.3V/5V
(LTC1515-3.3/5) using a logic pin.
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 power-on reset circuit forces the POR pin low
on initial power-up. The POR output remains low until
200ms (typ) after V
OUT
is in regulation.
The parts are short-circuit and overtemperature protected.
Battery life is maximized by very low operating currents
(I
CC
= 60µA typ, I
CC
< 1µA in shutdown). All three parts are
available in an SO-8 package.
, LTC and LT are registered trademarks of Linear Technology Corporation.
Adjustable/Selectable 3V, 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
Very Low Shutdown Current: < 1µA
Shutdown Disconnects Load from V
IN
V
OUT
Programmable to 3V/5V or 3.3V/5V
Short-Circuit and Overtemperature Protected
650kHz Switching Frequency
Open-Drain Power-On Reset Output
Daisy-Chained Control Outputs
Available in SO-8 Package
APPLICATIONS
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SIM Interface in GSM Cellular Telephones
Smart Card Readers
Local Power Supplies
Portable Equipment
TYPICAL APPLICATION
Programmable 3.3V/5V Power Supply with Power-On Reset
100k
LTC1515-X 5V Output vs Input Voltage
5.2
I
OUT
= 10mA
5/3 = 3V
OUTPUT VOLTAGE (V)
ON OFF
RESET
5V 3.3V
1
2
SHDN
V
OUT
8
V
OUT
= 3.3V OR 5V
I
OUT
= 50mA
5.1
7
POR
V
IN
LTC1515-3.3/5
3
6
5/3
C1
+
4
GND
C1
–
5
0.22µF
+
10µF
+
10µF
V
IN
4-CELL
NiCd
5.0
4.9
LTC1515 • TA01
4.8
2
U
U
U
3
4
5
8
6
7
INPUT VOLTAGE (V)
9
10
LT1515 • TA02
1
LTC1515 Series
ABSOLUTE
MAXIMUM
RATINGS
(Note 1)
V
IN
to GND ................................................ – 0.3V to 12V
V
OUT
to GND ............................................. – 0.3V to 12V
SHDN, 5/3, FB to GND .............................. – 0.3V to 12V
V
OUT
Short-Circuit Duration ............................. Indefinite
PACKAGE/ORDER I FOR ATIO
TOP VIEW
SHDN 1
POR 2
FB 3
GND 4
8
7
6
5
V
OUT
V
IN
C1
+
C1
–
ORDER PART
NUMBER
SHDN 1
LTC1515CS8
LTC1515IS8
S8 PART MARKING
1515
1515I
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
CONDITIONS
V
OUT
= 5V
V
OUT
= 3V/3.3V
V
OUT
= ADJ
2V
≤
V
IN
≤
8V, I
OUT
≤
15mA
3V
≤
V
IN
≤
8V, I
OUT
≤
50mA
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
LTC1515, V
FB
Ramping Negative
LTC1515
LTC1515, V
IN
= 3V, Step-Up Mode
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)
Full Load
V
IL
V
IH
5/3, SHDN = V
IN
5/3, SHDN = 0V
FB = 1.232V
I
SINK
= 100µA, V
IN
= 3V
q
q
q
q
q
q
q
q
q
q
q
q
q
q
q
q
q
q
q
q
q
V
OUT
= 3V (LTC1515-3/5)
V
OUT
= 3.3V (LTC1515-3.3/5)
V
OUT
= 5V (LTC1515-3/5, LTC1515-3.3/5)
V
FB
Feedback Voltage
V
FB
Feedback Hysteresis
Effective Output Resistance
V
IN
Operating Current
V
IN
Shutdown Current
Output Ripple
Switching Frequency
5/3, SHDN Input Threshold
5/3, SHDN Input Current
FB Input Current
POR Output Low Voltage
2
U
U
W
W W
U
W
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
TOP VIEW
8
7
6
5
V
OUT
V
IN
C1
+
C1
–
POR 2
5/3 3
GND 4
ORDER PART NUMBER
LTC1515CS8-3/5
LTC1515CS8-3.3/5
LTC1515IS8-3/5
LTC1515IS8-3.3/5
S8 PART MARKING
151535
515335
515I35
15I335
S8 PACKAGE
8-LEAD PLASTIC SO
T
JMAX
= 125°C,
θ
JA
= 110°C/W
MIN
2.7
2.0
2.0
2.88
2.88
3.17
3.17
4.8
4.8
1.190
TYP
MAX
10
8
10
UNITS
V
V
V
V
V
V
V
V
V
V
%
Ω
µA
µA
µA
µA
mV
P-P
kHz
V
V
µA
µA
nA
V
3.0
3.0
3.3
3.3
5.0
5.0
1.232
1
3.12
3.12
3.43
3.43
5.2
5.2
1.275
30
60
75
100
135
1
25
100
500
0.4
–1
–1
– 50
0.05
650
1.0
1.0
800
1.6
1
1
50
0.4
LTC1515 Series
ELECTRICAL CHARACTERISTICS
V
IN
= 2V to 10V, SHDN = 3V, C1 = 0.22µF, C
IN
= C
OUT
= 10µF unless otherwise noted (Note 2).
PARAMETER
POR Leakage Current
POR Trip Point (With Respect to V
OUT
)
POR Trip Point Hysteresis
I
OUT
Short-Circuit Current
t
ON
POR Delay
V
OUT
= 0V
Soft Start Turn-On Time
After V
OUT
Above POR Threshold
q
q
CONDITIONS
V
POR
= 5V
V
OUT
Ramping Negative
q
q
MIN
–1
– 10
TYP
– 7.5
1
12
4
MAX
1
–5
40
280
UNITS
µA
%
%
mA
ms
ms
140
200
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:
For V
IN
≥
8V, C
OUT
= 22µF.
TYPICAL PERFORMANCE CHARACTERISTICS
LTC1515-X
3.3V Efficiency vs Output Current
100
V
OUT
= 3.3V
T
A
= 25°C
80
V
IN
= 2V
EFFICIENCY (%)
80
V
IN
= 3.3V
60
V
IN
= 8V
OUTPUT VOLTAGE RIPPLE (mV
P-P
)
V
IN
= 4.4V
EFFICIENCY (%)
60
V
IN
= 2.7V
V
IN
= 6V
40
20
0
0.01
0.1
1
10
OUTPUT CURRENT (mA)
LTC1515-X 5V Output Voltage
Ripple vs Input Voltage
250
OUTPUT VOLTAGE RIPPLE (mV
P-P
)
3.45
C
OUT
= 10µF
150
C
OUT
= 22µF
100
C
OUT
= 47µF
OPERATING CURRENT (µA)
200
V
OUT
= 5V
I
OUT
= 10mA
T
A
= 25°C
OUTPUT VOLTAGE (V)
50
0
0
2
6
4
INPUT VOLTAGE (V)
8
10
1515 G04
U W
100
1515 G01
LTC1515-X
5V Efficiency vs Output Current
100
V
IN
= 2.7V
V
IN
= 6V
LTC1515-X 3.3V Output Voltage
Ripple vs Input Voltage
250
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
1515 G02
50
C
OUT
= 47µF
0
0
2
6
4
INPUT VOLTAGE (V)
8
10
1515 G03
LTC1515-X 3.3V Output Voltage
vs Input Voltage
120
V
OUT
= 3.3V
I
OUT
= 10mA
C
OUT
= 10µF
T
A
= 25°C
LTC1515-X Operating Current
vs Input Voltage
V
OUT
= 5V
I
OUT
= 0mA
100
3.40
3.35
80
25°C
60
85°C
–40°C
3.30
3.25
40
3.20
0
2
6
4
INPUT VOLTAGE (V)
8
10
1515 G05
20
0
2
6
4
INPUT VOLTAGE (V)
8
10
1515 G06
3
LTC1515 Series
TYPICAL PERFORMANCE CHARACTERISTICS
LTC1515-X
3V Efficiency vs Input Voltage
100
V
OUT
= 3V
I
OUT
= 10mA
T
A
= 25°C
80
100
V
OUT
= 3.3V
I
OUT
= 10mA
TA = 25°C
80
EFFICIENCY (%)
60
EFFICIENCY (%)
EFFICIENCY (%)
40
20
0
2
6
4
INPUT VOLTAGE (V)
LTC1515-X Shutdown Supply
Current vs Input Voltage
25
SHDN = 0V
POSITIVE SUPPLY CURRENT (µA)
20
15
85°C
25°C
5
–40°C
10
0
0
2
6
4
INPUT VOLTAGE (V)
8
10
1515 G12
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 part. 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.
POR (Pin 2):
Open-Drain Power-On Reset Output. This pin
will pull low upon initial power-up, during shutdown or
until V
OUT
has been within 6.5% of its regulated value for
more than 200ms typ.
5/3 (LTC1515-X) (Pin 3):
Output Voltage Select. A logic
high on the 5/3 pin will force V
OUT
to regulate to 5V. A logic
low will force V
OUT
to 3V (LTC1515-3/5) or 3.3V (LTC1515-
3.3/5). As with the SHDN pin, the 5/3 pin may be driven with
3V logic over the entire V
IN
range. The 5/3 pin may not float.
FB (LTC1515) (Pin 3):
Feedback Input. The voltage on this
pin is compared to the internal reference voltage (1.232V)
to keep the output in regulation. An external resistor divider
is required between V
OUT
and FB to adjust the output
voltage. Total divider resistance should not exceed 2M.
GND (Pin 4):
Ground. Should be tied to a ground plane for
best performance.
C1
–
(Pin 5):
Charge Pump Flying Capacitor, Negative
Terminal.
4
U W
8
10
1515 G09
LTC1515-X
3.3V Efficiency vs Input Voltage
100
LTC1515-X
5V Efficiency vs Input Voltage
V
OUT
= 5V
I
OUT
= 10mA
TA = 25°C
80
60
60
40
40
20
0
2
6
4
INPUT VOLTAGE (V)
8
10
1515 G07
20
2
4
8
6
INPUT VOLTAGE (V)
10
12
1515 G08
LTC1515-X Step-Down Mode
5V Load Transient Response
LTC1515-X Step-Up Mode
5V Load Transient Response
V
OUT
AC COUPLED
100mV/DIV
V
OUT
AC COUPLED
100mV/DIV
I
OUT
50mA/DIV
50mA
0mA
I
OUT
50mA/DIV
V
IN
= 8V, V
OUT
= 5V, C
OUT
= 10µF, T
A
= 25°C
1515 G10
V
IN
= 3.3V, V
OUT
= 5V, C
OUT
= 10µF, T
A
= 25°C
1515 G11
U
U
U
LTC1515 Series
PIN FUNCTIONS
C1
+
(Pin 6):
Charge Pump Flying Capacitor, Positive
Terminal.
V
IN
(Pin 7):
Charge Pump Input Voltage. May be between
2V and 10V. 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. Pin selectable to
either 3V/5V, 3.3V/5V or adjustable using an external
resistor divider (LTC1515). V
OUT
should be bypassed with
a
≥
10µF low ESR capacitor as close as possible to the pin
for best performance.
SI PLIFIED BLOCK DIGRAM
V
IN
SHDN
650kHz
OSCILLATOR
POR
RESET
COUNTER
EN
APPLICATIONS INFORMATION
Regulator Operation
The regulator section of the LTC1515, LTC1515-3/5 and
LTC1515-3.3/5 consists of a charge pump, reference,
comparator and some logic. The divided down output
voltage is compared to the internal reference voltage.
When the divided output drops below the reference volt-
age, the charge pump is enabled, which boosts the output
back into regulation. Hysteresis in the comparator forces
the regulator 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 parts
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.
U
W
W
U
U
U
U
W
U
C1
–
C1
+
STEP-UP/STEP-DOWN
CHARGE PUMP
V
OUT
(LTC1515-X)
(LTC1515-X)
–
EN
+
FB
(LTC1515)
V
OS
–
+
1.232V
V
REF
5/3
(LTC1515-X)
GND
LTC1515 • BD
5
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