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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: 120 Maximum Power Shutdown to 8A 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 8A 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.
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
Generating -15V from 15V
8 BOOST V+ 2 7 CAP+ OSC 3 6 GND SHDN 4 5 CAP- VOUT
Output Voltage vs Load Current, V + = 15V
-15 ROUT = 56 TA = 25C -14
OUTPUT VOLTAGE (V)
15V INPUT
+
10F
-15V OUTPUT 10F
1144 TA01
-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
PACKAGE/ORDER I FOR ATIO
TOP VIEW BOOST 1 CAP+ 2 GND 3 CAP- 4 8 7 6 5 V+ OSC SHDN VOUT
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................................................ 0C to 70C LTC1144I ............................................ - 40C to 85C Storage Temperature Range ................. - 65C to 150C Lead Temperature (Soldering, 10 sec).................. 300C
ORDER PART NUMBER LTC1144CN8 LTC1144IN8
N8 PACKAGE 8-LEAD PLASTIC DIP T JMAX = 110C, JA = 100C/W
TOP VIEW BOOST 1 CAP+ 2 GND 3 CAP- 4 8 7 6 5 V+ OSC SHDN VOUT
LTC1144CS8 LTC1144IS8 S8 PART MARKING 1144 1144I
S8 PACKAGE 8-LEAD PLASTIC SOIC T JMAX = 110C, JA = 130C/W
Consult factory for Military grade parts.
ELECTRICAL CHARACTERISTICS
V + = 15V, COSC = 0pF, TA = 25C, Test Circuit Figure 1, unless otherwise noted.
SYMBOL PARAMETER Supply Voltage Range IS Supply Current 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 0.10 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 kHz kHz % % A A
q q q
q q
0.002 56
0.002 56 90 10 4 93 99.9 0.5 4
ROUT
Output Resistance
q
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)
q
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 TA = 25C. 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: 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.
2
U
W
U
U
WW
W
LTC1144 TYPICAL PERFORMANCE CHARACTERISTICS
Output Resistance vs Supply Voltage
300 250
TA = 25C OSCILLATOR FREQUENCY (kHz)
OUTPUT RESISTANCE ()
OUTPUT RESISTANCE ()
200 150 100 50 0 2 4 6 10 12 14 8 SUPPLY VOLTAGE (V) 16 18
Oscillator Frequency as a Function of COSC
1000
TA = 25C 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), COSC (pF)
LTC1144 * TPC04
Output Voltage vs Load Current
0 TA = 25C V+ = 5V C1 = C2 = 10F BOOST = OPEN
10000
POWER CONVERSION EFFICIENCY (%)
-1
SUPPLY CURRENT (A)
OUTPUT VOLTAGE (V)
-2
-3 ROUT = 90 -4
-5
0
5
10 15 20 LOAD CURRENT (mA)
UW
LTC1144 * TPC01
Output Resistance vs Temperature
140 120 100 80 60 40 20 -55 -25 V + = 5V IL = 3mA
1000
Oscillator Frequency vs Supply Voltage
TA = 25C COSC = 0 BOOST = V +
100
V = 15V IL = 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 TA = 25C V + = 15V BOOST = V +
Output Voltage vs Load Current
0 TA = 25C V+ = 15V C1 = C2 = 10F BOOST = OPEN
-5
BOOST = OPEN OR GROUND 10
-10 ROUT = 56
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
TA = 25C C1 = C2 = 10F 1000 V + = 15V 100 V + = 5V 10
Power Conversion Efficiency and Supply Current vs Load Current
100 PEFF 80 IS 80
SUPPLY CURRENT (mA)
60
60
40
40 TA = 25C V+ = 15V 20 C1 = C2 = 10F 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 (%)
10F 90 10F 85 1F 80 1F 75 70 0.1 IL = 20mA 1 10 OSCILLATOR FREQUENCY (kHz) 100 IL = 3mA
OUTPUT RESISTANCE ()
80
PEFF
POWER CONVERSION EFFICIENCY (%)
60
40
IS
20
0
0
4
TA = 25C V + = 5V 10 C1 = C2 = 10F BOOST = OPEN (SEE TEST CIRCUIT) 0 12 16 20 8 LOAD CURRENT (mA)
LTC1144 * TPC10
Ripple Voltage vs Load Current
1500 V + = 5V TA = 25C C1 = C2 BOOST = 5V BOOST = OPEN 0.1F 0.1F 10F 500 1F
0
RIPPLE VOLTAGE (mV)
1000
OUTPUT VOLTAGE (V)
OUTPUT VOLTAGE (V)
1F
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. VOUT (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 connecting an external capacitor between this pin and ground. V + (Pin 8): Input Voltage.
4
UW
10F
LTC1144 * TPC13
Power Conversion Efficiency vs Oscillator Frequency
50
100 100F 95 100F TA = 25C, V + = 15V BOOST = OPEN
Output Resistance vs Oscillator Frequency
3000 TA = 25C V + = 15V
40
SUPPLY CURRENT (mA)
2000 10F 1F
30
20
1000
100F 0 0.1 1 10 OSCILLATOR FREQUENCY (kHz) 100
LTC1144 * TPC11
LTC1144 * TPC12
Output Voltage vs Load Current
V + = 5V TA = 25C C1 = C2 BOOST = 5V BOOST = OPEN 0.1F 10F 0.1F -3 1F 1F 10F -4
Output Voltage vs Load Current
0 V + = 15V TA = 25C C1 = C2 BOOST = 15V BOOST = OPEN
-1
-5
-2
0.1F -10 0.1F 1F 1F 10F 10F 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 10F 8 7 LTC1144 6 5 EXTERNAL OSCILLATOR R L V+ 15V IS
+
3 4
IL VOUT
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, 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 f RL C1 C2
1144 F02
V1 C2 REQUIV = 1 f x C1 RL
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 onresistance 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 x q = f x C1(V1 - V2) Rewriting in terms of voltage and impedance equivalence,
BOOST 10X (1) OSC OSC (7)
/2
I=
V1 - V2 V1 - V2 = 1 REQUIV f x C1
SHDN (6)
A new variable REQUIV has been defined such that REQUIV = 1/(f x C1). Thus, the equivalent circuit for the switchedcapacitor network is as shown in Figure 3.
Figure 4. LTC1144 Switched-Capacitor Voltage Converter Block Diagram
+
COSC
C2 10F
1144 F01
U
REQUIV V2
1144 F03
W
U
UO
CAP + (2)

+
C1
CAP - (4)
VOUT (5) C2
+
GND (3)
1144 F04
5
LTC1144
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 x C1) term and power efficiency will drop. 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.
100
POWER CONVERSION EFFICIENCY (%)
95 90 85 80 75 70
V + = 15V, C1 = C2 = 10F IL = 20mA, TA = 25C POWER CONVERSION EFFICIENCY
600 500
OUTPUT RESISTANCE ()
400 300 200
OUTPUT RESISTANCE
100 0 100
0.1
1 10 OSCILLATOR FREQUENCY (kHz)
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 8A. 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-
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 4A, 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.
6
+
U
V+ 9I BOOST (1) I OSC (7) 20pF SCHMITT TRIGGER 9I GND (3) I
1144 F06
W
U
UO
Figure 6. Oscillator
REQUIRED FOR TTL LOGIC NC 1 2 LTC1144 8 7 6 5 -(V +) C2
1144 F07
V+
100k OSC INPUT
+
C1
3 4
LTC1144
TYPICAL APPLICATI
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 56 resistor. The 56 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 2 8 7 LTC1144 6 5 10F
1144 F08
+
10F
3 4
TMIN TA TMAX
Figure 8. Negative Voltage Converter
At an oscillator frequency of 10kHz and C1 = 10F, the first term is: REQUIV =
(f
1
OSC / 2
) x C1
=
5 x 103 x 10 x 10-6
Notice that the above equation for REQUIV is not a capacitive reactance equation (X C = 1/C) and does not contain a 2 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 = 10F, the output impedance goes from 56 at fOSC = 10kHz to 250 at fOSC = 1kHz. As the 1/(f x C) term becomes large compared to the switch on-resistance term, the output resistance is determined by 1/(f x C) only. Voltage Doubling 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.
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.
+
UO
+
S
V IN 2V TO 18V 1 2 3 4 LTC1144 8 7 6 5 Vd + 1N4148 Vd 1N4148
+ +
+
10F
VOUT = 2(VIN - 1) 10F
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.
V+ 4V TO 36V 1 8 7 LTC1144 6 5
VOUT = -V +
C1 10F V+ 0.002% 2 TMIN TA TMAX IL 100nA
2
+
3 4
+
C2 10F
1144 F10
Figure 10. Ultra-Precision Voltage Divider
1
= 20
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).
1 VB 18V 8 7 LTC1144 6 5 C2 10F -VB /2 -9V VB /2 9V
+
C1 10F
2
+
3 4
OUTPUT COMMON
1144 F11
7
LTC1144
TYPICAL APPLICATI
Regulated -5V Output Voltage Figure 12 shows a regulated -5V output with a 9V input. With a 0mA to 5mA load current, the ROUT is below 20. Paralleling for Lower Output Resistance 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 x C1), increasing the capacitor size (C1) or increasing the frequency will be of more benefit than the paralleling circuit shown.
1 2 C1 10F 8 7 LTC1144 6 5 C1 10F 1 2
Figure 12. A Regulated - 5V Supply
V+
8 7 LTC1144 6 5 VOUT = -(V +) C2 20F
+
3 4
+
3 4
1/4 CD4077*
* THE EXCLUSIVE NOR GATE SYNCHRONIZES BOTH LTC1144s TO MINIMIZE RIPPLE
1144 F13
Figure 13. Paralleling for Lower Output Resistance
PACKAGE DESCRIPTION
0.300 - 0.320 (7.620 - 8.128)
Dimemsions in inches (millimeters) unless otherwise noted.
0.400 (10.160) MAX 8 7 6 5
0.045 - 0.065 (1.143 - 1.651)
0.130 0.005 (3.302 0.127)
N8 Package 8-Lead Plastic DIP
0.009 - 0.015 (0.229 - 0.381)
0.065 (1.651) TYP 0.125 (3.175) MIN 0.020 (0.508) MIN
(
+0.025 0.325 -0.015 +0.635 8.255 -0.381
)
0.045 0.015 (1.143 0.381) 0.100 0.010 (2.540 0.254)
1
2
3
0.018 0.003 (0.457 0.076) 0.189 - 0.197 (4.801 - 5.004)
0.010 - 0.020 x 45 (0.254 - 0.508)
S8 Package 8-Lead Plastic SOIC
0.053 - 0.069 (1.346 - 1.752) 0- 8 TYP
0.004 - 0.010 (0.101 - 0.254)
8
7
0.008 - 0.010 (0.203 - 0.254)
0.016 - 0.050 0.406 - 1.270
0.014 - 0.019 (0.355 - 0.483)
0.050 (1.270) BSC
0.228 - 0.244 (5.791 - 6.197)
*THESE DIMENSIONS DO NOT INCLUDE MOLD FLASH OR PROTRUSIONS. MOLD FLASH OR PROTRUSIONS SHALL NOT EXCEED 0.006 INCH (0.15mm).
1
2
8
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7487
(408) 432-1900 q FAX: (408) 434-0507 q TELEX: 499-3977
LT/GP 0494 10K * PRINTED IN USA
(c) LINEAR TECHNOLOGY CORPORATION 1994
+
+
U
UO
S
9V 1 2 8 7 LTC1144 6 5 36k 2N2369
+
1F
3 4
300k - 5V 100F
1144 F12
0.250 0.010 (6.350 0.254)
4
6
5
0.150 - 0.157 (3.810 - 3.988)
3
4

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