LTC1522
Micropower, Regulated
5V Charge Pump
DC/DC Converter
FEATURES
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DESCRIPTION
The LTC
®
1522 is a micropower charge pump DC/DC
converter that produces a regulated 5V output from a 2.7V
to 5V input supply. Extremely low supply current (6µA
typical with no load, < 1µA in shutdown) and low external
parts count (one 0.22µF flying capacitor and two 10µF
capacitors at V
IN
and V
OUT
) make the LTC1522 ideally
suited for small, light load battery-powered applications.
Typical efficiency (V
IN
= 3V) exceeds 75% with load
currents between 50µA and 20mA. Modulating the SHDN
pin keeps the typical efficiency above 75% with load
currents all the way down to 10µA.
The LTC1522 has thermal shutdown and can survive a
continuous short from V
OUT
to GND. In shutdown the
load is disconnected from V
IN
. The part is available in
8-pin MSOP and SO packages. The LTC1522 is pin
compatible with the LTC1516 in applications where
V
IN
≥
2.7V and I
OUT
≤
20mA.
, LTC and LT are registered trademarks of Linear Technology Corporation.
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Ultralow Power: Typical Operating I
CC
= 6µA
Short-Circuit/Thermal Protected
Regulated 5V
±4%
Output Voltage
2.7V to 5V Input Range
No Inductors
Very Low I
CC
in Shutdown: < 1µA
Output Current: 10mA (V
IN
≥
2.7V)
20mA (V
IN
≥
3V)
Shutdown Disconnects Load from V
IN
Internal Oscillator: 700kHz
Compact Application Circuit (< 0.1 in
2
)
8-Pin MSOP and SO Packages
APPLICATIONS
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SIM Interface Supplies for GSM Cellular Telephones
Li-Ion Battery Backup Supplies
Local 3V to 5V Conversion
Smart Card Readers
PCMCIA Local 5V Supplies
TYPICAL APPLICATION
Regulated 5V Output from a 2.7V to 5V Input
V
IN
2.7V TO 5V
1
Efficiency vs Output Current
90
V
IN
= 3V
+
10µF
2
3
NC
V
IN
V
OUT
C
+
0.22µF
NC
SHDN
LTC1522
GND
C
–
8
7
6
5
ON/OFF
80
EFFICIENCY (%)
+
10µF 4
70
SHDN = 0V
60
V
OUT
= 5V
±4%
I
OUT
= 0mA TO 10mA, V
IN
≥
2.7V
I
OUT
= 0mA TO 20mA, V
IN
≥
3V
1522 TA01
50
0.01
U
U
U
LOW I
Q
MODE
(SEE FIGURE 2)
0.1
1
10
OUTPUT CURRENT (mA)
100
1522 TA02
1
LTC1522
ABSOLUTE
MAXIMUM
RATINGS
(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
PACKAGE/ORDER INFORMATION
ORDER PART
NUMBER
TOP VIEW
NC 1
V
IN
2
V
OUT
3
C
+
4
8
7
6
5
NC
SHDN
GND
C
–
LTC1522CMS8
MS8 PART MARKING
LTCG
MS8 PACKAGE
8-LEAD PLASTIC MSOP
T
JMAX
= 125°C,
θ
JA
= 160°C/ W
Consult factory for Industrial and Military grade parts.
ELECTRICAL CHARACTERISTICS
V
IN
= 2.7V to 5V, C
FLY
= 0.22µF, C
IN
= C
OUT
= 10µF, T
MIN
to T
MAX
unless otherwise specified. (Note 2)
SYMBOL PARAMETER
V
IN
Input Voltage
V
OUT
Output Voltage
I
CC
Operating Supply Current
Shutdown Supply Current
Output Ripple
Efficiency
Switching Frequency
SHDN Input Threshold
SHDN Input Current
V
OUT
Turn-On Time
CONDITIONS
q
f
OSC
V
IH
V
IL
I
IH
I
IL
t
ON
2.7V
≤
V
IN
≤
5V, I
OUT
≤
10mA
3V
≤
V
IN
≤
5V, I
OUT
≤
20mA
2.7V
≤
V
IN
≤
5V, I
OUT
= 0mA, SHDN = 0V
2.7V
≤
V
IN
≤
3.6V, I
OUT
= 0mA, SHDN = V
IN
3.6V < V
IN
≤
5V, I
OUT
= 0mA, SHDN = V
IN
V
IN
= 3V, I
OUT
= 10mA
V
IN
= 3V, I
OUT
= 10mA
Oscillator Free Running
V
SHDN
= V
IN
V
SHDN
= 0V
V
IN
= 3V, I
OUT
= 0mA
The
q
denotes specifications which apply over the specified 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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Commercial Temperature Range ................ 0°C to 70°C
Extended Commercial Operating
Temperature Range (Note 2) ............. – 40°C to 85°C
Storage Temperature Range ................ – 65°C to 150°C
Lead Temperature (Soldering, 10 sec)................. 300°C
TOP VIEW
NC 1
V
IN
2
V
OUT
3
C
+
4
8 NC
7 SHDN
6 GND
5 C
–
ORDER PART
NUMBER
LTC1522CS8
S8 PART MARKING
1522
S8 PACKAGE
8-LEAD PLASTIC SO
T
JMAX
= 125°C,
θ
JA
= 150°C/ W
q
q
q
q
q
MIN
2.7
4.8
4.8
TYP
5.0
5.0
6
0.005
70
82
700
MAX
5
5.2
5.2
15
1
2.5
q
q
q
q
(0.7)(V
IN
)
0.4
–1
–1
1
1
1
UNITS
V
V
V
µA
µA
µA
mV
P-P
%
kHz
V
V
µA
µA
ms
Note 2:
C grade device specifications are guaranteed over the 0°C to 70°C
temperature range. In addition, C grade device specifications are assured
over the – 40°C to 85°C temperature range by design or correlation, but
are not production tested.
LTC1522
TYPICAL PERFORMANCE CHARACTERISTICS
Output Voltage vs Input Voltage
5.15
I
OUT
= 10mA
C
OUT
= 10µF
5.10
OUTPUT VOLTAGE (V)
V
RIPPLE P-P
(mV)
EFFICIENCY (%)
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)
7
T
A
= 70°C
T
A
= 25°C
OUTPUT VOLTAGE (V)
6
T
A
= 0°C
5
4
2.5
3.0
4.0
4.5
3.5
INPUT VOLTAGE (V)
PIN FUNCTIONS
NC (Pin 1):
No Connect.
V
IN
(Pin 2):
Input Supply Voltage. Bypass V
IN
with a
≥
3.3µF low ESR capacitor.
V
OUT
(Pin 3):
5V Output Voltage (V
OUT
= 0V in Shutdown).
Bypass V
OUT
with a
≥
3.3µF low ESR capacitor.
C
+
(Pin 4):
Flying Capacitor, Positive Terminal.
C
–
(Pin 5):
Flying Capacitor, Negative Terminal.
GND (Pin 6):
Ground.
SHDN (Pin 7):
Active High CMOS Logic-Level Shutdown
Input. Drive SHDN low to enable the DC/DC converter. Do
not float.
NC (Pin 8):
No Connect.
U W
1522 G01
1522 G04
Efficiency vs Input Voltage
90
I
OUT
= 10mA
T
A
= 25°C
80
200
250
Output Ripple vs Input Voltage
I
OUT
= 10mA
C
FLY
= 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
1522 G02
0
2.5
3.0
4.0
4.5
3.5
INPUT VOLTAGE (V)
5.0
1522 G03
Typical Output Voltage
vs Output Current
5.2
T
A
= 25°C
C
FLY
= 0.1µF
C
OUT
= 6.8µF
Load Transient Response
5.1
I
OUT
0mA TO 10mA
10mA/DIV
5.0
V
IN
= 2.7V
4.9
V
OUT
AC COUPLED
50mV/DIV
V
IN
= 3V
V
IN
= 3.3V
V
IN
= 3V
C
OUT
= 10µF
500µs/DIV
1522 G06
5.0
4.8
0
40
60
20
OUTPUT CURRENT (mA)
80
1522 G05
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LTC1522
BLOCK DIAGRAM
V
IN
C
IN
10µF
+
S2A
C
+
S1A
1µA
S2B
C
–
CLOCK 1
S1B
CLOCK 2
CONTROL
LOGIC
COMP1
C
FLY
0.22µF
CHARGE PUMP SHOWN IN DISCHARGE CYCLE
APPLICATIONS INFORMATION
Operation
The LTC1522 uses a switched capacitor charge pump to
boost V
IN
to a regulated 5V
±4%
output voltage. Regula-
tion 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 COMP1. When the charge pump is enabled, a 2-phase,
nonoverlapping clock controls the charge pump switches.
Clock 1 closes the S1 switches which enables the flying
capacitor to charge up to the V
IN
voltage. Clock 2 closes
the S2 switches that stack C
FLY
in series with V
IN
and
connect the top plate of C
FLY
to the output capacitor at
V
OUT
. This sequence of charging and discharging contin-
ues at a free-running frequency of 700kHz (typ) until the
output has risen to the upper trip point of COMP1 and the
charge pump is disabled. When the charge pump is
disabled, the LTC1522 draws only 4µA (typ) from V
IN
which provides high efficiency at low load conditions.
In shutdown mode, all circuitry is turned off and the part
draws only leakage current 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 should not
be floated; it must be driven with a logic high or low.
Short-Circuit/Thermal Protection
During short-circuit conditions, the LTC1522 will draw
between 100mA and 200mA from V
IN
causing a rise in
the junction temperature. On-chip thermal shutdown
circuitry disables the charge pump once the junction
temperature exceeds
≈
160°C, and reenables the charge
pump once the junction temperature falls back to
≈
145°C.
The LTC1522 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
(< 0.5Ω) 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 (aluminum capacitors are not recommended
because of their high ESR). If the input source impedance
is very low, C
IN
may not be needed. Increasing the size of
C
OUT
to 10µF or greater will reduce output voltage ripple.
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W
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SHDN
+
V
OUT
C
OUT
10µF
+
–
V
REF
CHARGE PUMP
LTC1522 BD
U
U
LTC1522
APPLICATIONS INFORMATION
A ceramic capacitor is recommended for the flying capaci-
tor with a value in the range of 0.1µF to 0.22µF. Note that
a large value flying cap (> 0.22µF) will increase output
ripple unless C
OUT
is also increased. For very low load
applications, C
FLY
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 LTC1522 operation produces voltage ripple on the
V
OUT
pin. Output voltage ripple is required for the LTC1522
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 50mV
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. A large flying capacitor (> 0.22µF) also increases
ripple 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 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 1).
LTC1522
3
V
OUT
U
W
U
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+
15µF
TANTALUM
1µF
CERAMIC
V
OUT
5V
LTC1522
3
V
OUT
3.9Ω
+
10µF
TANTALUM
+
10µF
TANTALUM
V
OUT
5V
1522 F01
Figure 1. Output Ripple Reduction Techniques
In low load or high V
IN
applications, smaller values for
C
FLY
may be used to reduce output ripple. A smaller flying
capacitor (0.01µF to 0.047µF) delivers 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.
Inrush Currents
During normal operation, V
IN
will experience current tran-
sients in the 50mA to 100mA range whenever the charge
pump is enabled. During start-up, these inrush currents
may approach 250mA. For this reason, it is important to
minimize the source resistance between the input supply
and the V
IN
pin. Too much source resistance may result in
regulation problems or even prevent start-up.
Ultralow Quiescent Current (I
Q
= 2.1µA)
Regulated Supply
The LTC1522 contains an internal resistor divider (refer to
the Block Diagram) that draws only 1µA (typ) from V
OUT
.
During no-load conditions, the internal load causes a
droop rate of only 100mV per second on V
OUT
with
C
OUT
= 10µF. Applying a 2Hz to 100Hz, 95% to 98% duty
cycle signal to the SHDN pin ensures that the circuit of
Figure 2 comes out of shutdown frequently enough to
maintain regulation during no-load or low-load condi-
tions. Since the part spends nearly all of its time in
shutdown, the no-load quiescent current (see Figure 3a) is
approximately equal to (V
OUT
)(1µA)/(V
IN
)(Efficiency).
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