LTC1144 Switched-Capacitor Wide Input Range Voltage Converter with Shutdown U 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 UO APPLICATI ■ ■ ■ ■ ■ ■ 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. UO ■ S 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 U U RATI GS W W W W AXI U U 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 U W 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 U W 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 U U U 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. U W U UO 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 W U U UO 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 UO 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 U 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