LINER LTC1144IN8 Switched-capacitor wide input range voltage converter with shutdown Datasheet

LTC1144
Switched-Capacitor
Wide Input Range
Voltage Converter
with Shutdown
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DESCRIPTIO
FEATURES
■
■
■
■
■
■
■
■
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
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APPLICATI
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■
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■
■
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
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-bytwo, voltage level shifter, and four power MOSFETs. A
special logic circuit will prevent the power N-channel
switch substrate from turning on.
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■
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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.
TYPICAL APPLICATI
Output Voltage vs Load Current, V + = 15V
Generating –15V from 15V
–15
LTC1144
10µF
ROUT = 56Ω
TA = 25°C
15V INPUT
–14
–15V OUTPUT
10µF
1144 TA01
OUTPUT VOLTAGE (V)
+
8
BOOST
V+
2
7
CAP+
OSC
3
6
GND
SHDN
4
5
CAP–
VOUT
+
1
–13
–12
–11
–10
0
10
30
40
20
LOAD CURRENT (mA)
50
1144 TA02
1
LTC1144
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ABSOLUTE
PACKAGE/ORDER I FOR ATIO
(Note 1)
TOP VIEW
Supply Voltage (V +) (Transient) .............................. 20V
Supply Voltage (V +) (Operating) ............................. 18V
Input Voltage on Pins 1, 6, 7
(Note 2) ............................ – 0.3V < VIN < (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
ORDER PART
NUMBER
BOOST 1
8
V+
CAP+ 2
7
OSC
GND 3
6
SHDN
CAP– 4
5
VOUT
LTC1144CN8
LTC1144IN8
N8 PACKAGE
8-LEAD PLASTIC DIP
T JMAX = 110°C, θJA = 100°C/W
TOP VIEW
LTC1144CS8
LTC1144IS8
BOOST 1
8
V+
CAP+ 2
7
OSC
GND 3
6
SHDN
CAP– 4
5
VOUT
S8 PART MARKING
1144
1144I
S8 PACKAGE
8-LEAD PLASTIC SOIC
T JMAX = 110°C, θJA = 130°C/W
Consult factory for Military grade parts.
ELECTRICAL CHARACTERISTICS
V + = 15V, COSC = 0pF, TA = 25°C, Test Circuit Figure 1, unless otherwise noted.
SYMBOL PARAMETER
Supply Voltage Range
IS
Supply Current
ROUT
Output Resistance
CONDITIONS
RL = 10k
RL = ∞, Pins 1, 6 No Connection,
fOSC = 10kHz
SHDN = 0V, RL = ∞, Pins 1, 7
No Connection
V + = 5V, RL = ∞, Pins 1, 6
No Connection, fOSC = 4kHz
V + = 5V, SHDN = 0V, RL = ∞,
Pins 1, 7 No Connection
V + = 15V, IL = 20mA at 10kHz
●
MIN
2
●
●
LTC1144C
TYP
MAX
18
1.1
1.3
0.008 0.03
●
0.002
●
56
●
fOSC
V + = 5V, IL = 3mA at 4kHz
Oscillator Frequency
V + = 15V (Note 3)
V + = 5V
Power Efficiency
RL = 2k at 10kHz
Voltage Conversion Efficiency
RL = ∞
Oscillator Sink or Source Current V + = 5V (VOSC = 0V to 5V)
V + = 15V (VOSC = 0V to 15V)
The ● denotes specifications which apply over the full operating
temperature range; all other limits and typicals at TA = 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
2
●
●
●
90
97.0
90
10
4
93
99.9
0.5
4
MIN
2
0.10
0.13
0.015
LTC1144I
TYP
MAX
18
1.1
1.6
0.008 0.035
UNITS
V
mA
mA
mA
0.10
0.15
0.018
mA
mA
mA
100
140
300
Ω
Ω
Ω
kHz
kHz
%
%
µA
µA
0.002
100
120
250
56
90
97.0
90
10
4
93
99.9
0.5
4
inputs from sources operating from external supplies be applied prior to
power-up of the LTC1144.
Note 3: fOSC is tested with COSC = 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.
LTC1144
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TYPICAL PERFORMANCE CHARACTERISTICS
Output Resistance
vs Supply Voltage
140
300
200
150
100
50
V + = 5V
IL = 3mA
100
80
60
+
V = 15V
IL = 20mA
40
0
2
6
10 12 14
8
SUPPLY VOLTAGE (V)
4
16
20
–55 –25
18
OSCILLATOR FREQUENCY (kHz)
120
OUTPUT RESISTANCE (Ω)
100
LTC1144 • TPC01
BOOST = V +
10
1
BOOST = OPEN OR GROUND
0.1
BOOST = V +
100
BOOST = OPEN OR GROUND
10
100
SUPPLY CURRENT (µA)
30
LTC1144 • TPC07
50
1000
V + = 15V
100
V + = 5V
10
1
0.01
PEFF
80
100
LTC1144 • TPC08
80
IS
60
60
40
40
20
0
1
10
0.1
OSCILLATOR FREQUENCY (kHz)
60
100
100
TA = 25°C
C1 = C2 = 10µF
25
20
30
40
LOAD CURRENT (mA)
0
TA = 25°C
V+ = 15V
20
C1 = C2 = 10µF
BOOST = OPEN
(SEE TEST CIRCUIT)
0
10
30
40
50
20
LOAD CURRENT (mA)
SUPPLY CURRENT (mA)
10
15
20
LOAD CURRENT (mA)
10
Power Conversion Efficiency and
Supply Current vs Load Current
–4
5
–10
LTC1144 • TPC06
10000
ROUT = 90Ω
–5
0
125
Supply Current as a Function of
Oscillator Frequency
0
18
TA = 25°C
V+ = 15V
C1 = C2 = 10µF
BOOST = OPEN
LTC1144 • TPC05
Output Voltage vs Load Current
16
–15
0
25
50
75
TEMPERATURE (°C)
LTC1144 • TPC04
–3
8
10 12
14
SUPPLY VOLTAGE (V)
ROUT = 56Ω
1
–55 –25
100
10
1000
1
10000
EXTERNAL CAPACITANCE (PIN 7 TO GND), COSC (pF)
–2
6
Output Voltage vs Load Current
0
OUTPUT VOLTAGE (V)
OSCILLATOR FREQUENCY (kHz)
OSCILLATOR FREQUENCY (kHz)
100
TA = 25°C
V+ = 5V
C1 = C2 = 10µF
BOOST = OPEN
4
LTC1144 • TPC03
TA = 25°C
V + = 15V
0.01
OUTPUT VOLTAGE (V)
2
Oscillator Frequency
vs Temperature
TA = 25°C
V + = 15V
0
BOOST = OPEN OR GROUND
10
125
1000
–1
BOOST = V +
100
LTC1144 • TPC02
Oscillator Frequency as a
Function of COSC
1000
TA = 25°C
COSC = 0
1
50
25
75
0
TEMPERATURE (°C)
POWER CONVERSION EFFICIENCY (%)
OUTPUT RESISTANCE (Ω)
1000
TA = 25°C
250
–5
Oscillator Frequency
vs Supply Voltage
Output Resistance vs Temperature
LTC1144 • TPC09
3
LTC1144
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TYPICAL PERFORMANCE CHARACTERISTICS
Power Conversion Efficiency
vs Oscillator Frequency
30
60
20
IS
TA = 25°C
V + = 5V
10
C1 = C2 = 10µF
BOOST = OPEN
(SEE TEST CIRCUIT)
0
12
16
20
8
LOAD CURRENT (mA)
20
4
0
100µF
95
100µF
10µF
90
10µF
85
IL = 3mA
1µF
80
1µF
10µF
1000
0
0.1
100
–1
0.1µF
10µF
500
1µF
Output Voltage vs Load Current
0
V + = 5V
TA = 25°C
C1 = C2
BOOST = 5V
BOOST = OPEN
0.1µF 10µF
–2
0.1µF
1µF
1µF
–3
10µF
–5
V + = 15V
TA = 25°C
C1 = C2
BOOST = 15V
BOOST = OPEN
0.1µF
–10
0.1µF
–4
10
0.1
1
LOAD CURRENT (mA)
100
–5
0.001
0.01
10
0.1
1
LOAD CURRENT (mA)
LTC1144 • TPC13
100
–15
0.001
LTC1144 • G14
1µF
1µF
10µF
10µF
10µF
0
0.01
100
LTC1144 • TPC12
Output Voltage vs Load Current
0.1µF
1
10
OSCILLATOR FREQUENCY (kHz)
LTC1144 • TPC11
0
1µF
1µF
100µF
1
10
OSCILLATOR FREQUENCY (kHz)
0.1
OUTPUT VOLTAGE (V)
RIPPLE VOLTAGE (mV)
1000
2000
IL = 20mA
70
Ripple Voltage vs Load Current
V + = 5V
TA = 25°C
C1 = C2
BOOST = 5V
BOOST =
OPEN
TA = 25°C
V + = 15V
75
LTC1144 • TPC10
1500
3000
TA = 25°C, V + = 15V
BOOST = OPEN
OUTPUT VOLTAGE (V)
40
POWER CONVERSION EFFICIENCY (%)
40
SUPPLY CURRENT (mA)
POWER CONVERSION EFFICIENCY (%)
PEFF
80
0
100
50
100
Output Resistance
vs Oscillator Frequency
OUTPUT RESISTANCE (Ω)
Power Conversion Efficiency and
Supply Current vs Load Current
0.01
10
0.1
1
LOAD CURRENT (mA)
100
LTC1144 • TPC15
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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.
SHDN (Pin 6): Shutdown Pin. Tie to V + pin or leave floating
for normal operation. Tie to ground when in shutdown
mode.
CAP – (Pin 4): Negative Terminal for Pump Capacitor.
OSC (Pin 7): Oscillator Input Pin. This pin can be overdriven
with an external clock or can be slowed down by connecting an external capacitor between this pin and ground.
VOUT (Pin 5): Output of the Converter.
V + (Pin 8): Input Voltage.
GND (Pin 3): Ground Reference.
4
LTC1144
TEST CIRCUITS
V+
15V
IS
1
8
2
C1
10µF
+
3
EXTERNAL
OSCILLATOR R
L
7
LTC1144
4
6
IL
5
COSC
C2
10µF
VOUT
+
1144 F01
Figure 1.
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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, discharging 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
V2
f
RL
C1
C2
1144 F02
REQUIV
V1
C2
REQUIV =
A new variable REQUIV has been defined such that REQUIV
= 1/(f × C1). Thus, the equivalent circuit for the switchedcapacitor network is as shown in Figure 3.
1144 F03
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)
BOOST
SW1
φ
10X
(1)
Rewriting in terms of voltage and impedance equivalence,
V1 − V2 V1 − V2
=
 1  REQUIV
 f × C1


1
f × C1
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 onresistance and output voltage ripple, the simple theory,
although not exact, provides an intuitive feel for how the
device works.
If the switch is cycled f times per second, the charge
transfer per unit time (i.e., current) is:
I=
RL
Figure 3. Switched-Capacitor Equivalent Circuit
Figure 2. Switched-Capacitor Building Block
I = f × ∆q = f × C1(V1 – V2)
V2
OSC
OSC
(7)
÷2
φ
CAP +
(2)
SW2
+
C1
CAP –
(4)
VOUT
(5)
+
SHDN
(6)
GND
(3)
C2
1144 F04
Figure 4. LTC1144 Switched-Capacitor
Voltage Converter Block Diagram
5
LTC1144
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APPLICATI
S I FOR ATIO
and hence the efficiency, is set by the output impedance.
As frequency is decreased, the output impedance will
eventually be dominated by the 1/(f × C1) term and power
efficiency will drop.
V+
9I
BOOST
(1)
Note also that power efficiency decreases as frequency
goes up. This is caused by internal switching losses which
occur due to some finite charge being lost on each
switching cycle. This charge loss per unit cycle, when
multiplied by the switching frequency, becomes a current
loss. At high frequency this loss becomes significant and
the power efficiency starts to decrease.
POWER CONVERSION EFFICIENCY (%)
300
80
70
200
OUTPUT
RESISTANCE
0.1
1144 F06
Figure 6. Oscillator
OUTPUT RESISTANCE (Ω)
400
85
75
≈20pF
I
GND
(3)
500
POWER
CONVERSION
EFFICIENCY
90
9I
SCHMITT
TRIGGER
600
V + = 15V, C1 = C2 = 10µF
IL = 20mA, TA = 25°C
95
OSC
(7)
100
1
10
OSCILLATOR FREQUENCY (kHz)
V+
REQUIRED FOR
TTL LOGIC
NC
+
C1
1
8
2
7
3
LTC1144
4
6
5
100k
OSC INPUT
–(V +)
+
100
I
0
100
C2
1144 F07
1144 F05
Figure 7. External Clocking
Figure 5. Power Conversion Efficiency and Output
Resistance vs Oscillator Frequency
SHDN (Pin 6)
The LTC1144 has a SHDN pin that will disable the internal
oscillator when it is pulled low. The supply current will also
drop to 8µA.
OSC (Pin 7) and Boost (Pin 1)
The switching frequency can be raised, lowered or driven
from an external source. Figure 6 shows a functional
diagram of the oscillator circuit.
By connecting the boost pin (pin 1) to V +, the charge and
discharge current is increased, and hence the frequency is
increased by approximately 10 times. Increasing the frequency will decrease output impedance and ripple for
higher load currents.
Loading pin 7 with more capacitance will lower the frequency. Using the boost (pin 1) in conjunction with exter-
6
nal capacitance on pin 7 allows user selection of the
frequency over a wide range.
Driving the LTC1144 from an external frequency source
can be easily achieved by driving pin 7 and leaving the
boost pin open as shown in Figure 7. The output current
from pin 7 is small, typically 4µA, so a logic gate is capable
of driving this current. The choice of using a CMOS logic
gate is best because it can operate over a wide supply
voltage range (3V to 15V) and has enough voltage swing
to drive the internal Schmitt trigger shown in Figure 6. For
5V applications, a TTL logic gate can be used by simply
adding an external pull-up resistor (see Figure 7).
Capacitor Selection
External capacitors C1 and C2 are not critical. Matching is
not required, nor do they have to be high quality or tight
tolerance. Aluminum or tantalum electrolytics are excellent
choices, with cost and size being the only consideration.
LTC1144
UO
TYPICAL APPLICATI
S
V IN
2V TO 18V
Negative Voltage Converter
Figure 8 shows a typical connection which will provide a
negative supply from an available positive supply. This
circuit operates over full temperature and power supply
ranges without the need of any external diodes.
The output voltage (pin 5) characteristics of the circuit are
those of a nearly ideal voltage source in series with a 56Ω
resistor. The 56Ω output impedance is composed of two
terms: 1) the equivalent switched capacitor resistance
(see Theory of Operation), and 2) a term related to the onresistance of the MOS switches.
V+
2V TO 18V
1
8
2
3
10µF
Vd
1N4148
+
5
+
+
10µF
) × C1
=
VOUT = 2(VIN – 1)
10µF
1144 F09
Figure 9. Voltage Doubler
Ultra-Precision Voltage Divider
An ultra-precision voltage divider is shown in Figure 10. To
achieve the 0.0002% accuracy indicated, the load current
should be kept below 100nA. However, with a slight loss
in accuracy, the load current can be increased.
1
VOUT = –V +
10µF
C1
10µF
1144 F08
1
5 × 103 × 10 × 10−6
+
Notice that the above equation for REQUIV is not a capacitive reactance equation (X C = 1/ωC) and does not contain
a 2π term.
The exact expression for output impedance is extremely
complex, but the dominant effect of the capacitor is clearly
shown in Figure 5. For C1 = C2 = 10µF, the output
impedance goes from 56Ω at fOSC = 10kHz to 250Ω at
fOSC = 1kHz. As the 1/(f × C) term becomes large compared
to the switch on-resistance term, the output resistance is
determined by 1/(f × C) only.
3
7
LTC1144
6
4
V+ ±0.002%
2
TMIN ≤ TA ≤ TMAX
IL ≤ 100nA
= 20Ω
8
2
At an oscillator frequency of 10kHz and C1 = 10µF, the first
term is:
OSC / 2
6
4
Figure 8. Negative Voltage Converter
(f
LTC1144
3
Vd +
1N4148
V+
4V TO 36V
5
TMIN ≤ TA ≤ TMAX
1
7
6
4
REQUIV =
8
2
7
LTC1144
+
+
1
+
5
C2
10µF
1144 F10
Figure 10. Ultra-Precision Voltage Divider
Battery Splitter
A common need in many systems is to obtain (+) and (–)
supplies from a single battery or single power supply
system. Where current requirements are small, the circuit
shown in Figure 11 is a simple solution. It provides
symmetrical ± output voltages, both equal to one half the
input voltage. The output voltages are both referenced to
pin 3 (output common).
VB
18V
+
C1
10µF
+
1
8
2
7
3
LTC1144
4
Voltage Doubling
VB /2
9V
6
5
–VB /2
–9V
+
Figure 9 shows a two-diode capacitive voltage doubler.
With a 15V input, the output is 29.45V with no load and
28.18V with a 10mA load.
C2
10µF
OUTPUT
COMMON
1144 F11
Figure 11. Battery Splitter
Information furnished by Linear Technology Corporation is believed to be accurate and reliable.
However, no responsibility is assumed for its use. Linear Technology Corporation makes no representation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
7
LTC1144
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TYPICAL APPLICATI
S
9V
Regulated –5V Output Voltage
1
Figure 12 shows a regulated –5V output with a 9V input.
With a 0mA to 5mA load current, the ROUT is below 20Ω.
8
2
+
7
LTC1144
3
1µF
6
4
2N2369
5
36k
Paralleling for Lower Output Resistance
300k
Additional flexibility of the LTC1144 is shown in Figure 13.
Two LTC1144s are connected in parallel to provide a lower
effective output resistance. However, if the output resistance is dominated by 1/(f × C1), increasing the capacitor
size (C1) or increasing the frequency will be of more
benefit than the paralleling circuit shown.
+
3
LTC1144
6
5
4
1144 F12
Figure 12. A Regulated – 5V Supply
V+
8
1
7
2
C1
10µF
+
8
1
– 5V
100µF
7
2
+
C1
10µF
3
LTC1144
6
5
4
VOUT = –(V +)
+
C2
20µF
1/4 CD4077*
* THE EXCLUSIVE NOR GATE
SYNCHRONIZES BOTH LTC1144s
TO MINIMIZE RIPPLE
1144 F13
Figure 13. Paralleling for Lower Output Resistance
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PACKAGE DESCRIPTION
Dimemsions in inches (millimeters) unless otherwise noted.
0.300 – 0.320
(7.620 – 8.128)
N8 Package
8-Lead Plastic DIP
0.009 – 0.015
(0.229 – 0.381)
(
+0.025
0.325 –0.015
+0.635
8.255
–0.381
)
0.045 – 0.065
(1.143 – 1.651)
0.400
(10.160)
MAX
0.130 ± 0.005
(3.302 ± 0.127)
8
7
6
5
0.065
(1.651)
TYP
0.250 ± 0.010
(6.350 ± 0.254)
0.045 ± 0.015
(1.143 ± 0.381)
0.100 ± 0.010
(2.540 ± 0.254)
0.125
(3.175)
MIN
0.020
(0.508)
MIN
1
2
4
3
0.018 ± 0.003
(0.457 ± 0.076)
0.189 – 0.197
(4.801 – 5.004)
0.010 – 0.020
× 45°
(0.254 – 0.508)
S8 Package
8-Lead Plastic SOIC
0.008 – 0.010
(0.203 – 0.254)
0.053 – 0.069
(1.346 – 1.752)
7
6
5
0°– 8° TYP
0.016 – 0.050
0.406 – 1.270
0.014 – 0.019
(0.355 – 0.483)
*THESE DIMENSIONS DO NOT INCLUDE MOLD FLASH OR PROTRUSIONS.
MOLD FLASH OR PROTRUSIONS SHALL NOT EXCEED 0.006 INCH (0.15mm).
8
8
0.004 – 0.010
(0.101 – 0.254)
Linear Technology Corporation
0.050
(1.270)
BSC
0.150 – 0.157
(3.810 – 3.988)
0.228 – 0.244
(5.791 – 6.197)
1
2
3
4
LT/GP 0494 10K • PRINTED IN USA
1630 McCarthy Blvd., Milpitas, CA 95035-7487
(408) 432-1900 ● FAX: (408) 434-0507 ● TELEX: 499-3977
 LINEAR TECHNOLOGY CORPORATION 1994
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