LTC1144
Switched-Capacitor
Wide Input Range
Voltage Converter
with Shutdown
FEATURES
s
s
s
s
s
s
DESCRIPTIO
s
s
Wide Operating Supply Voltage Range: 2V to 18V
Boost Pin (Pin 1) for Higher Switching Frequency
Simple Conversion of 15V to –15V Supply
Low Output Resistance: 120Ω Maximum
Power Shutdown to 8µA with SHDN Pin
Open Circuit Voltage Conversion Efficiency:
99.9% Typical
Power Conversion Efficiency: 93% Typical
Easy to Use
The LTC1144 is a monolithic CMOS switched-capacitor
voltage converter. It performs supply voltage conversion
from positive to negative from an input range of 2V to 18V,
resulting in complementary output voltages of –2V to
–18V. Only two noncritical external capacitors are needed
for the charge pump and charge reservoir functions.
The converter has an internal oscillator that can be
overdriven by an external clock or slowed down when
connected to a capacitor. The oscillator runs at a 10kHz
frequency when unloaded. A higher frequency outside the
audio band can also be obtained if the Boost Pin is tied to
V
+
. The SHDN pin reduces supply current to 8µA and can
be used to save power when the converter is not in use.
The LTC1144 contains an internal oscillator, divide-by-
two, voltage level shifter, and four power MOSFETs. A
special logic circuit will prevent the power N-channel
switch substrate from turning on.
APPLICATI
s
s
s
s
s
s
s
S
Conversion of 15V to
±15V
Supplies
Inexpensive Negative Supplies
Data Acquisition Systems
High Voltage Upgrade to LTC1044 or 7660
Voltage Division and Multiplications
Automotive Applications
Battery Systems with Wall Adapter/Charger
TYPICAL APPLICATI
LTC1144
1
2
BOOST
CAP
+
GND
CAP
–
Generating –15V from 15V
8
7
6
5
10µF
1144 TA01
Output Voltage vs Load Current, V
+
= 15V
–15
R
OUT
= 56Ω
T
A
= 25°C
–14
OUTPUT VOLTAGE (V)
V
+
OSC
SHDN
V
OUT
15V INPUT
+
10µF
3
4
–15V OUTPUT
–13
–12
–11
–10
0
10
30
40
20
LOAD CURRENT (mA)
50
1144 TA02
U
+
UO
UO
1
LTC1144
ABSOLUTE
(Note 1)
AXI U
RATI GS
20V
18V
PACKAGE/ORDER I FOR ATIO
TOP VIEW
BOOST 1
CAP
+
Supply Voltage (V
+
) (Transient) ..............................
Supply Voltage (V
+
) (Operating) .............................
8
7
6
5
V
+
ORDER PART
NUMBER
LTC1144CN8
LTC1144IN8
Input Voltage on Pins 1, 6, 7
(Note 2) ............................ – 0.3V < V
IN
< (V
+
) + 0.3V
Output Short-Circuit Duration
V
+
≤
10V .................................................... Indefinite
V
+
≤
15V ........................................................ 30 sec
V
+
≤
20V ............................................. Not Protected
Power Dissipation ............................................. 500mW
Operating Temperature Range
LTC1144C................................................ 0°C to 70°C
LTC1144I ............................................ – 40°C to 85°C
Storage Temperature Range ................. – 65°C to 150°C
Lead Temperature (Soldering, 10 sec).................. 300°C
2
OSC
SHDN
V
OUT
GND 3
CAP
–
4
N8 PACKAGE
8-LEAD PLASTIC DIP
T
JMAX
= 110°C,
θ
JA
= 100°C/W
TOP VIEW
BOOST 1
CAP
+
2
GND 3
CAP
–
8
7
6
5
V
+
OSC
SHDN
V
OUT
LTC1144CS8
LTC1144IS8
S8 PART MARKING
1144
1144I
4
S8 PACKAGE
8-LEAD PLASTIC SOIC
T
JMAX
= 110°C,
θ
JA
= 130°C/W
Consult factory for Military grade parts.
ELECTRICAL CHARACTERISTICS
V
+
= 15V, C
OSC
= 0pF, T
A
= 25°C, Test Circuit Figure 1, unless otherwise noted.
SYMBOL PARAMETER
Supply Voltage Range
I
S
Supply Current
CONDITIONS
R
L
= 10k
R
L
=
∞
, Pins 1, 6 No Connection,
f
OSC
= 10kHz
SHDN = 0V, R
L
=
∞
, Pins 1, 7
No Connection
V
+
= 5V, R
L
=
∞
, Pins 1, 6
No Connection, f
OSC
= 4kHz
V
+
= 5V, SHDN = 0V, R
L
=
∞
,
Pins 1, 7 No Connection
V
+
= 15V, I
L
= 20mA at 10kHz
V
+
= 5V, I
f
OSC
Oscillator Frequency
L
= 3mA at 4kHz
q
q
q
MIN
2
LTC1144C
TYP
MAX
18
1.1
1.3
0.008 0.03
0.10
0.13
0.015
100
120
250
MIN
2
LTC1144I
TYP
MAX
18
1.1
1.6
0.008 0.035
0.10
0.15
0.018
100
140
300
UNITS
V
mA
mA
mA
mA
mA
mA
Ω
Ω
Ω
kHz
kHz
%
%
µA
µA
q
q
0.002
56
0.002
56
90
10
4
93
99.9
0.5
4
R
OUT
Output Resistance
q
q
V
+
= 15V (Note 3)
V
+
= 5V
Power Efficiency
R
L
= 2k at 10kHz
Voltage Conversion Efficiency
R
L
=
∞
Oscillator Sink or Source Current V
+
= 5V (V
OSC
= 0V to 5V)
V
+
= 15V (V
OSC
= 0V to 15V)
q
q
90
97.0
90
10
4
93
99.9
0.5
4
90
97.0
The
q
denotes specifications which apply over the full operating
temperature range; all other limits and typicals at T
A
= 25°C.
Note 1:
Absolute maximum ratings are those values beyond which the life
of a device may be impaired.
Note 2:
Connecting any input terminal to voltages greater than V
+
or less
than ground may cause destructive latch-up. It is recommended that no
inputs from sources operating from external supplies be applied prior to
power-up of the LTC1144.
Note 3:
f
OSC
is tested with C
OSC
= 100pF to minimize the effects of test
fixture capacitance loading. The 0pF frequency is correlated to this 100pF
test point, and is intended to simulate the capacitance at pin 7 when the
device is plugged into a test socket and no external capacitor is used.
2
U
W
U
U
W W
W
LTC1144
TYPICAL PERFORMANCE CHARACTERISTICS
Output Resistance
vs Supply Voltage
300
250
T
A
= 25°C
OSCILLATOR FREQUENCY (kHz)
OUTPUT RESISTANCE (Ω)
OUTPUT RESISTANCE (Ω)
200
150
100
50
0
2
4
6
10 12 14
8
SUPPLY VOLTAGE (V)
16
18
Oscillator Frequency as a
Function of C
OSC
1000
T
A
= 25°C
V
+
= 15V
OSCILLATOR FREQUENCY (kHz)
100
BOOST = V
+
10
OSCILLATOR FREQUENCY (kHz)
100
OUTPUT VOLTAGE (V)
1
BOOST = OPEN OR GROUND
0.1
0.01
100
10
1000
1
10000
EXTERNAL CAPACITANCE (PIN 7 TO GND), C
OSC
(pF)
LTC1144 • TPC04
Output Voltage vs Load Current
0
T
A
= 25°C
V
+
= 5V
C1 = C2 = 10µF
BOOST = OPEN
10000
POWER CONVERSION EFFICIENCY (%)
–1
SUPPLY CURRENT (µA)
OUTPUT VOLTAGE (V)
–2
–3
R
OUT
= 90Ω
–4
–5
0
5
10
15
20
LOAD CURRENT (mA)
U W
LTC1144 • TPC01
Output Resistance vs Temperature
140
120
100
80
60
40
20
–55 –25
V
+
= 5V
I
L
= 3mA
1000
Oscillator Frequency
vs Supply Voltage
T
A
= 25°C
C
OSC
= 0
BOOST = V
+
100
V
+
= 15V
I
L
= 20mA
10
BOOST = OPEN OR GROUND
1
50
25
75
0
TEMPERATURE (°C)
100
125
2
4
6
8
10 12
14
SUPPLY VOLTAGE (V)
16
18
LTC1144 • TPC02
LTC1144 • TPC03
Oscillator Frequency
vs Temperature
1000
T
A
= 25°C
V
+
= 15V
BOOST = V
+
Output Voltage vs Load Current
0
T
A
= 25°C
V
+
= 15V
C1 = C2 = 10µF
BOOST = OPEN
–5
BOOST = OPEN OR GROUND
10
–10
R
OUT
= 56Ω
1
–55 –25
–15
0
25
50
75
TEMPERATURE (°C)
100
125
0
10
20
30
40
LOAD CURRENT (mA)
50
60
LTC1144 • TPC05
LTC1144 • TPC06
Supply Current as a Function of
Oscillator Frequency
100
T
A
= 25°C
C1 = C2 = 10µF
1000
V
+
= 15V
100
V
+
= 5V
10
Power Conversion Efficiency and
Supply Current vs Load Current
100
P
EFF
80
I
S
80
SUPPLY CURRENT (mA)
60
60
40
40
T
A
= 25°C
V
+
= 15V
20
C1 = C2 = 10µF
BOOST = OPEN
(SEE TEST CIRCUIT)
0
10
30
40
50
20
LOAD CURRENT (mA)
LTC1144 • TPC09
20
25
30
1
0.01
0
1
10
0.1
OSCILLATOR FREQUENCY (kHz)
100
0
LTC1144 • TPC07
LTC1144 • TPC08
3
LTC1144
TYPICAL PERFORMANCE CHARACTERISTICS
Power Conversion Efficiency and
Supply Current vs Load Current
100
POWER CONVERSION EFFICIENCY (%)
10µF
90
10µF
85
1µF
80
1µF
75
70
0.1
I
L
= 20mA
1
10
OSCILLATOR FREQUENCY (kHz)
100
I
L
= 3mA
OUTPUT RESISTANCE (Ω)
80
P
EFF
POWER CONVERSION EFFICIENCY (%)
60
40
I
S
20
0
0
4
T
A
= 25°C
V
+
= 5V
10
C1 = C2 = 10µF
BOOST = OPEN
(SEE TEST CIRCUIT)
0
12
16
20
8
LOAD CURRENT (mA)
LTC1144 • TPC10
Ripple Voltage vs Load Current
1500
V
+
= 5V
T
A
= 25°C
C1 = C2
BOOST = 5V
BOOST =
OPEN
0.1µF
0.1µF
10µF
500
1µF
0
RIPPLE VOLTAGE (mV)
1000
OUTPUT VOLTAGE (V)
OUTPUT VOLTAGE (V)
1µF
0
0.01
10
0.1
1
LOAD CURRENT (mA)
PI FU CTIO S
Boost (Pin 1):
This pin will raise the oscillator frequency
by a factor of 10 if tied high.
CAP
+
(Pin 2):
Positive Terminal for Pump Capacitor.
GND (Pin 3):
Ground Reference.
CAP
–
(Pin 4):
Negative Terminal for Pump Capacitor.
V
OUT
(Pin 5):
Output of the Converter.
SHDN (Pin 6):
Shutdown Pin. Tie to V
+
pin or leave floating
for normal operation. Tie to ground when in shutdown
mode.
OSC (Pin 7):
Oscillator Input Pin. This pin can be overdriven
with an external clock or can be slowed down by connect-
ing an external capacitor between this pin and ground.
V
+
(Pin 8):
Input Voltage.
4
U W
10µF
LTC1144 • TPC13
Power Conversion Efficiency
vs Oscillator Frequency
50
100
100µF
95
100µF
T
A
= 25°C, V
+
= 15V
BOOST = OPEN
Output Resistance
vs Oscillator Frequency
3000
T
A
= 25°C
V
+
= 15V
40
SUPPLY CURRENT (mA)
2000
10µF
1µF
30
20
1000
100µF
0
0.1
1
10
OSCILLATOR FREQUENCY (kHz)
100
LTC1144 • TPC11
LTC1144 • TPC12
Output Voltage vs Load Current
V
+
= 5V
T
A
= 25°C
C1 = C2
BOOST = 5V
BOOST = OPEN
0.1µF 10µF
0.1µF
–3
1µF
1µF
10µF
–4
Output Voltage vs Load Current
0
V
+
= 15V
T
A
= 25°C
C1 = C2
BOOST = 15V
BOOST = OPEN
–1
–5
–2
0.1µF
–10
0.1µF
1µF
1µF
10µF
10µF
0.01
10
0.1
1
LOAD CURRENT (mA)
100
100
–5
0.001
0.01
10
0.1
1
LOAD CURRENT (mA)
100
–15
0.001
LTC1144 • G14
LTC1144 • TPC15
U
U
U
LTC1144
TEST CIRCUITS
1
2
C1
+
10µF
3
4
LTC1144
8
7
6
5
EXTERNAL
OSCILLATOR R
L
V
+
15V
I
S
I
L
V
OUT
Figure 1.
APPLICATI
S I FOR ATIO
Theory of Operation
To understand the theory of operation of the LTC1144, a
review of a basic switched-capacitor building block is
helpful.
In Figure 2, when the switch is in the left position, capacitor
C1 will charge to voltage V1. The total charge on C1 will be
q1 = C1V1. The switch then moves to the right, discharg-
ing C1 to voltage V2. After this discharge time, the charge
on C1 is q2 = C1V2. Note that charge has been transferred
from the source V1 to the output V2. The amount of charge
transferred is:
∆q
= q1 – q2 = C1(V1 – V2)
V1
f
R
L
C1
C2
1144 F02
V1
C2
R
EQUIV
=
1
f
×
C1
R
L
Figure 3. Switched-Capacitor Equivalent Circuit
V2
Examination of Figure 4 shows that the LTC1144 has the
same switching action as the basic switched-capacitor
building block. With the addition of finite switch on-
resistance and output voltage ripple, the simple theory,
although not exact, provides an intuitive feel for how the
device works.
For example, if you examine power conversion efficiency
as a function of frequency (see Figure 5), this simple
theory will explain how the LTC1144 behaves. The loss,
V
+
(8)
SW1
SW2
Figure 2. Switched-Capacitor Building Block
If the switch is cycled f times per second, the charge
transfer per unit time (i.e., current) is:
I = f
× ∆q
= f
×
C1(V1 – V2)
Rewriting in terms of voltage and impedance equivalence,
BOOST
10X
(1)
OSC
OSC
(7)
÷
2
I
=
V1
−
V2 V1
−
V2
=
1
R
EQUIV
f
×
C1
SHDN
(6)
A new variable R
EQUIV
has been defined such that R
EQUIV
= 1/(f
×
C1). Thus, the equivalent circuit for the switched-
capacitor network is as shown in Figure 3.
Figure 4. LTC1144 Switched-Capacitor
Voltage Converter Block Diagram
+
C
OSC
C2
10µF
1144 F01
U
R
EQUIV
V2
1144 F03
W
U
UO
CAP
+
(2)
φ
φ
+
C1
CAP
–
(4)
V
OUT
(5)
C2
+
GND
(3)
1144 F04
5
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