Micropower DC-DC Converter ADP1173 a FEATURES Operates From 2.0 V to 30 V Input Voltages Only 110 mA Supply Current (Typical) Step-Up or Step-Down Mode Operation Very Few External Components Required Low Battery Detector On-Chip User-Adjustable Current Limit Internal 1 A Power Switch Fixed or Adjustable Output Voltage Versions 8-Pin DIP or SO-8 Package FUNCTIONAL BLOCK DIAGRAMS SET ADP1173 VIN The ADP1173 is part of a family of step-up/step-down switching regulators that operates from an input supply voltage of as little as 2 V to 12 V in step-up mode and to 30 V in step-down mode. The ADP1173 consumes as little as 110 µA in standby mode, making it ideal for applications that need low quiescent current. An auxiliary gain amplifier can serve as a low battery detector, linear regulator (under voltage lockout) or error amplifier. GAIN BLOCK/ ERROR AMP ILIM SW1 1.245V REFERENCE A1 OSCILLATOR DRIVER COMPARATOR APPLICATIONS Notebook and Palmtop Computers Cellular Telephones Flash Memory Vpp Generators 3 V to 5 V, 5 V to 12 V Converters 9 V to 5 V, 12 V to 5 V Converters Portable Instruments LCD Bias Generators GENERAL DESCRIPTION AO A2 GND SW2 FB SET ADP1173-3.3 ADP1173-5 ADP1173-12 AO A2 VIN GAIN BLOCK/ ERROR AMP 1.245V REFERENCE R1 SW1 A1 OSCILLATOR COMPARATOR DRIVER SW2 ADP1173-3.3: R1 = 456kΩ ADP1173-5: R1 = 250kΩ ADP1173-12: R1 = 87.4kΩ R2 753kΩ GND ILIM SENSE The ADP1173 can deliver 80 mA at 5 V from a 3 V input in step-up configuration or 100 mA at 5 V from a 12 V input in step-down configuration. For input voltages of less than 2 V use the ADP1073. REV. 0 Information furnished by Analog Devices is believed to be accurate and reliable. However, no responsibility is assumed by Analog Devices for its use, nor for any infringements of patents or other rights of third parties which may result from its use. No license is granted by implication or otherwise under any patent or patent rights of Analog Devices. One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A. Tel: 617/329-4700 World Wide Web Site: http://www.analog.com Fax: 617/326-8703 © Analog Devices, Inc., 1997 ADP1173–SPECIFICATIONS (@ T = 08C to +708C, V A Model Symbol Conditions QUIESCENT CURRENT IQ IN = 3 V unless otherwise noted) Typ Max Units Switch Off 110 150 µA QUIESCENT CURRENT, BOOST MODE IQ CONFIGURATION No Load, TA = +25°C ADP1173-3.3 ADP1173-5 ADP1173-12 135 135 250 INPUT VOLTAGE Step-Up Mode Step-Down Mode 2.0 ADP11731 1.20 ADP1173-3.32 ADP1173-52 ADP1173-122 3.14 4.75 11.4 VIN COMPARATOR TRIP POINT VOLTAGE OUTPUT SENSE VOLTAGE VOUT Min µA µA µA 12.6 30 V V 1.245 1.30 V 3.30 5.00 12.0 3.46 5.25 12.6 V V V COMPARATOR HYSTERESIS ADP1173 5 12 mV OUTPUT HYSTERESIS ADP1173-3.3 ADP1173-5 ADP1173-12 13 20 50 35 55 100 mV mV mV 16 24 32 kHz Full Load 43 55 63 % ILIM Tied to VIN 15 23 32 µs OSCILLATOR FREQUENCY fOSC DUTY CYCLE SWITCH ON TIME tON FEEDBACK PIN BIAS CURRENT ADP1173, VFB = 0 V 60 290 nA SET PIN BIAS CURRENT VSET = VREF 70 150 nA ISINK = 100 µA, VSET = 1.00 V 0.15 0.4 V 2.0 V ≤ VIN ≤ 5 V 5 V ≤ VIN ≤ 30 V 0.2 0.02 0.4 0.075 %/V %/V VIN = 3.0 V, ISW = 650 mA VIN = 5.0 V, ISW = 1 A, TA = +25°C VIN = 5.0 V, ISW = 1 A 0.5 0.85 V 0.8 1.0 1.4 V V 1.1 1.5 1.7 V V GAIN BLOCK OUTPUT LOW VOL REFERENCE LINE REGULATION SWSAT VOLTAGE, STEP-UP MODE SWSAT VOLTAGE, STEP-DOWN MODE GAIN BLOCK GAIN VSAT VSAT AV VIN = 12 V, TA = +25°C, ISW = 650 mA VIN = 12 V, ISW = 650 mA RL = 100 kΩ3 220 Ω from ILIM to VIN TA = +25°C CURRENT LIMIT CURRENT LIMIT TEMPERATURE COEFFICIENT SWITCH-OFF LEAKAGE CURRENT MAXIMUM EXCURSION BELOW GND VSW2 400 1000 V/V 400 mA –0.3 %/°C Measured at SW1 Pin TA = +25°C 1 10 µA ISW1 ≤ 10 µA, Switch Off TA = +25°C –400 –350 mV NOTES 1 This specification guarantees that both the high and low trip points of the comparator fall within the 1.20 V to 1.30 V range. 2 The output voltage waveform will exhibit a sawtooth shape due to the comparator hysteresis. The output voltage on the fixed output versions will always be within the specified range. 3 100 kΩ resistor connected between a 5 V source and the AO pin. Specifications subject to change without notice. –2– REV. 0 ADP1173 ABSOLUTE MAXIMUM RATINGS* PIN CONFIGURATIONS Supply Voltage (VIN) . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36 V SW1 Pin Voltage (VSW1) . . . . . . . . . . . . . . . . . . . . . . . . . 50 V SW2 Pin Voltage (VSW2) . . . . . . . . . . . . . . . . . . –0.5 V to VIN Feedback Pin Voltage (ADP1173) . . . . . . . . . . . . . . . . . . . 5 V Sense Pin Voltage (ADP1173, –3.3, –5, –12) . . . . . . . . . 36 V Maximum Power Dissipation . . . . . . . . . . . . . . . . . . 500 mW Maximum Switch Current . . . . . . . . . . . . . . . . . . . . . . . .1.5 A Operating Temperature Range . . . . . . . . . . . . . 0°C to +70°C Storage Temperature Range . . . . . . . . . . . . . –65°C to 150°C Lead Temperature, (Soldering, 10 sec) . . . . . . . . . . . . +300°C *Stresses above those listed under Absolute Maximum Ratings may cause permanent damage to the device. This is a stress rating only; functional operation of the device at these or any other conditions above those listed in the operational sections of this specification is not implied. Exposure to absolute maximum ratings for extended periods of time may affect device reliability. N-8 8-Lead Plastic DIP ILIM 1 VIN 2 ADP1173 Output Voltage Package Options* ADP1173AN ADP1173AR ADP1173AN-3.3 ADP1173AR-3.3 ADP1173AN-5 ADP1173AR-5 ADP1173AN-12 ADP1173AR-12 ADJ ADJ 3.3 V 3.3 V 5V 5V 12 V 12 V N-8 SO-8 N-8 SO-8 N-8 SO-8 N-8 SO-8 + +5V OUTPUT AT 100mA 56Ω 470µF 4X NICAD OR ALKALINE CELLS 1 2 ILIM VIN 470kΩ SET GND 5 + AO 6 + 470µF 2 ADP1173 7 SET SW1 3 TOP VIEW (Not to Scale) 4 5 GND *FIXED VERSIONS 8 FB (SENSE)* 6 AO 5 GND SW2 4 *FIXED VERSIONS PIN FUNCTION DESCRIPTIONS Mnemonic Function ILIM For normal conditions this pin is connected to VIN. When lower current is required, a resistor should be connected between ILIM and VIN. Limiting the switch current to 400 mA is achieved by connecting a 220 Ω resistor. VIN Input Voltage. SW1 Collector Node of Power Transistor. For step-down configuration, connect to VIN; for step-up configuration, connect to an inductor/diode. SW2 Emitter Node of Power Transistor. For stepdown configuration, connect to inductor/ diode; for step-up configuration, connect to ground. Do not allow this pin to drop more than a diode drop below ground. GND Ground. AO Auxiliary Gain (GB) Output. The open collector can sink 100 µA. SET Gain Amplifier Input. The amplifier has positive input connected to the SET pin and negative input is connected to 1.245 V reference. FB/SENSE On the ADP1173 (adjustable) version this pin is connected to the comparator input. On the ADP1173-3.3, ADP1173-5 and ADP1173-12, the pin goes directly to the internal application resistor that sets the output voltage. 470µF SW2 FB 8 4 1 VIN SW2 75kΩ SW1 3 ADP1173 7 IRF7203 ILIM 7 SET TOP VIEW 3 (Not to Scale) 6 AO *N = Plastic DIP, SO = Small Outline Package. L1* 100µH 8 FB (SENSE)* SW1 ORDERING GUIDE Model SO-8 8-Lead Plastic SO 240Ω 24kΩ *L1 = COILTRONICS CTX100-4 Figure 1. Step-Up or Step-Down Converter CAUTION ESD (electrostatic discharge) sensitive device. Electrostatic charges as high as 4000 V readily accumulate on the human body and test equipment and can discharge without detection. Although the ADP1173 features proprietary ESD protection circuitry, permanent damage may occur on devices subjected to high energy electrostatic discharges. Therefore, proper ESD precautions are recommended to avoid performance degradation or loss of functionality. REV. 0 –3– WARNING! ESD SENSITIVE DEVICE ADP1173 –Typical Performance Characteristics 1.2 1.6 VIN = 3V 0.6 VIN = 5V 0.4 0.2 900 SWITCH CURRENT – mA VIN = 2V 0.8 1000 VCE(SAT) 1.2 SWITCH ON VOLTAGE – V VCE (SAT) – V 1.0 1100 1.4 1.0 0.8 0.6 0.4 700 600 500 400 300 0.2 0 0.4 0.6 0.8 1.0 SWITCH CURRENT – A 1.2 Figure 2. Saturation Voltage vs. Switch Current in Step-Up Mode VIN =24V WITH L = 500µH @ VOUT = 5V 120 110 500 400 300 VIN =12V WITH L = 250µH @ VOUT = 5V 100 70 60 50 30 20 0 1000 RLIM – Ω Figure 5. Maximum Switch Current vs. RLIM in Step-Down Mode 25.5 80 25 70 24.5 24 23.5 23 OSCILLATOR FREQUENCY 22.5 22 3 5 20 25 10 15 INPUT VOLTAGE – Volts 30 Figure 8. Oscillator Frequency vs. Input Voltage 0 QUIESCENT CURRENT 100 90 80 70 60 40 –40 100 200 300 400 500 600 700 800 900 SWITCH CURRENT – mA 0 25 70 85 TEMPERATURE – °C Figure 7. Quiescent Current vs. Temperature 450 60 VIN = 3V 50 40 30 20 10 –40 1000 50 Figure 6. Supply Current vs. Switch Current SET PIN BIAS CURRENT – nA OSCILLATOR FREQUENCY – kHz VIN = 2V 10 0 100 21.5 VIN = 5V 40 FEEDBACK PIN BIAS CURRENT – nA 200 80 100 RLIM – Ω Figure 4. Maximum Switch Current vs. RLIM in Step-Up Mode 90 SUPPLY CURRENT – mA SWITCH CURRENT – mA 600 100 10 0.75 100 800 700 0.15 0.25 0.35 0.45 0.55 0.65 SWITCH CURRENT – A Figure 3. Switch ON Voltage vs. Switch Current in Step-Down Mode 1000 900 200 0.0 0.05 QUIESCENT CURRENT – µA 0.2 2V < VIN < 5V 800 0 25 70 85 TEMPERATURE – °C Figure 9. Set Pin Bias Current vs. Temperature –4– 400 350 300 250 200 VIN = 3V 150 100 50 0 –40 0 25 70 85 TEMPERATURE – °C Figure 10. Feedback Pin Bias Current vs. Temperature REV. 0 ADP1173 APPLICATIONS Theory of Operation COMPONENT SELECTION General Notes on Inductor Selection The ADP1173 is a flexible, low power switch mode power supply (SMPS) controller. The regulated output voltage can be greater than the input voltage (boost or step-up mode) or less than the input (buck or step-down mode). This device uses a gated-oscillator technique to provide very high performance with low quiescent current. When the ADP1173 internal power switch turns on, current begins to flow in the inductor. Energy is stored in the inductor core while the switch is on, and this stored energy is then transferred to the load when the switch turns off. Both the collector and the emitter of the switch transistor are accessible on the ADP1173, so the output voltage can be higher, lower or of opposite polarity than the input voltage. A functional block diagram of the ADP1173 is shown on the front page. The internal 1.245 V reference is connected to one input of the comparator, while the other input is externally connected (via the FB pin) to a feedback network connected to the regulated output. When the voltage at the FB pin falls below 1.245 V, the 24 kHz oscillator turns on. A driver amplifier provides base drive to the internal power switch, and the switching action raises the output voltage. When the voltage at the FB pin exceeds 1.245 V, the oscillator is shut off. While the oscillator is off, the ADP1173 quiescent current is only 110 µA. The comparator includes a small amount of hysteresis, which ensures loop stability without requiring external components for frequency compensation. The maximum current in the internal power switch can be set by connecting a resistor between VIN and the ILIM pin. When the maximum current is exceeded, the switch is turned OFF. The current limit circuitry has a time delay of about 2 µs. If an external resistor is not used, connect ILIM to VIN. Further information on ILIM is included in the Limiting the Switch Current section of this data sheet. The ADP1173 internal oscillator provides 23 µs ON and 19 µs OFF times, which is ideal for applications where the ratio between VIN and VOUT is roughly a factor of two (such as converting +3 V to + 5 V). However, wider range conversions (such as generating +12 V from a +5 V supply) can easily be accomplished. An uncommitted gain block on the ADP1173 can be connected as a low battery detector. The inverting input of the gain block is internally connected to the 1.245 V reference. The noninverting input is available at the SET pin. A resistor divider, connected between VIN and GND with the junction connected to the SET pin, causes the AO output to go LOW when the low battery set point is exceeded. The AO output is an open collector NPN transistor which can sink 100 µA. The ADP1173 provides external connections for both the collector and emitter of its internal power switch, which permits both step-up and step-down modes of operation. For the stepup mode, the emitter (pin SW2) is connected to GND and the collector (pin SW1) drives the inductor. For step-down mode, the emitter drives the inductor while the collector is connected to VIN. The output voltage of the ADP1173 is set with two external resistors. Three fixed-voltage models are also available: ADP1173-3.3 (+3.3 V), ADP1173-5 (+5 V) and ADP1173-12 (+12 V). The fixed-voltage models are identical to the ADP1173, except that laser-trimmed voltage-setting resistors are included on the chip. On the fixed-voltage models of the ADP1173, simply connect the feedback pin (Pin 8) directly to the output voltage. REV. 0 To specify an inductor for the ADP1173, the proper values of inductance, saturation current and dc resistance must be determined. This process is not difficult, and specific equations for each circuit configuration are provided in this data sheet. In general terms, however, the inductance value must be low enough to store the required amount of energy (when both input voltage and switch ON time are at a minimum) but high enough that the inductor will not saturate when both VIN and switch ON time are at their maximum values. The inductor must also store enough energy to supply the load without saturating. Finally, the dc resistance of the inductor should be low, so that excessive power will not be wasted by heating the windings. For most ADP1173 applications, an inductor of 47 µH to 470 µH, with a saturation current rating of 300 mA to 1 A and dc resistance <1 Ω is suitable. Ferrite core inductors which meet these specifications are available in small, surfacemount packages. To minimize Electro-Magnetic Interference (EMI), a toroid or pot core type inductor is recommended. Rod core inductors are a lower cost alternative if EMI is not a problem. CALCULATING THE INDUCTOR VALUE Selecting the proper inductor value is a simple three-step process: 1. Define the operating parameters: minimum input voltage, maximum input voltage, output voltage and output current. 2. Select the appropriate conversion topology (step-up, stepdown, or inverting). 3. Calculate the inductor value, using the equations in the following sections. Inductor Selection—Step-Up Converter In a step-up, or boost, converter (Figure 14), the inductor must store enough power to make up the difference between the input voltage and the output voltage. The power that must be stored is calculated from the equation: P L = (V OUT +V D –V IN(MIN ) ) × ( IOUT ) (1) where VD is the diode forward voltage (≈ 0.5 V for a 1N5818 Schottky). Energy is only stored in the inductor while the ADP1173 switch is ON, so the energy stored in the inductor on each switching cycle must be must be equal to or greater than: PL f OSC in order for the ADP1173 to regulate the output voltage. –5– (2) ADP1173 When the internal power switch turns ON, current flow in the inductor increases at the rate of: I L (t) = –R′t V IN 1– e L R′ When selecting an inductor, the peak current must not exceed the maximum switch current of 1.5 A. If the equations shown above result in peak currents > 1.5 A, the ADP1073 should be considered. This device has a 72% duty cycle, so more energy is stored in the inductor on each cycle. This results in greater output power. (3) where L is in henrys and R' is the sum of the switch equivalent resistance (typically 0.8 Ω at +25°C) and the dc resistance of the inductor. In most applications, where the voltage drop across the switch is small compared to VIN , a simpler equation can be used: I L (t) = V IN t L The peak current must be evaluated for both minimum and maximum values of input voltage. If the switch current is high when VIN is at its minimum, then the 1.5 A limit may be exceeded at the maximum value of VIN. In this case, the ADP1173’s current limit feature can be used to limit switch current. Simply select a resistor (using Figure 4) that will limit the maximum switch current to the IPEAK value calculated for the minimum value of VIN. This will improve efficiency by producing a constant IPEAK as VIN increases. See the Limiting the Switch Current section of this data sheet for more information. (4) Replacing “t” in the above equation with the ON time of the ADP1173 (23 µs, typical) will define the peak current for a given inductor value and input voltage. At this point, the inductor energy can be calculated as follows: 1 E L = LI 2 PEAK 2 Note that the switch current limit feature does not protect the circuit if the output is shorted to ground. In this case, current is only limited by the dc resistance of the inductor and the forward voltage of the diode. (5) As previously mentioned, EL must be greater than PL/fOSC so the ADP1173 can deliver the necessary power to the load. For best efficiency, peak current should be limited to 1 A or less. Higher switch currents will reduce efficiency, because of increased saturation voltage in the switch. High peak current also increases output ripple. As a general rule, keep peak current as low as possible to minimize losses in the switch, inductor and diode. Inductor Selection—Step-Down Converter The step-down mode of operation is shown in Figure 15. Unlike the step-up mode, the ADP1173’s power switch does not saturate when operating in the step-down mode. Therefore, switch current should be limited to 650 mA in this mode. If the input voltage will vary over a wide range, the ILIM pin can be used to limit the maximum switch current. If higher output current is required, the ADP1111 should be considered. In practice, the inductor value is easily selected using the equations above. For example, consider a supply that will generate 9 V at 50 mA from a 3 V source. The inductor power required is, from Equation 1: The first step in selecting the step-down inductor is to calculate the peak switch current as follows: P L = (9V + 0.5V – 3V )×(50 mA) = 325 mW I PEAK = On each switching cycle, the inductor must supply: PL f OSC 325 mW = =13.5 µJ 24 kHz VSW = voltage drop across the switch VD = diode drop (0.5 V for a 1N5818) IOUT = output current VOUT = the output voltage VIN = the minimum input voltage V IN 3V t= 23 µs =138 µH I L(MAX ) 500 mA As previously mentioned, the switch voltage is higher in stepdown mode than step-up mode. VSW is a function of switch current and is therefore a function of VIN, L, time and VOUT. For most applications, a VSW value of 1.5 V is recommended. Substituting a standard inductor value of 100 µH, with 0.2 Ω dc resistance, will produce a peak switch current of: I PEAK = (6) where DC = duty cycle (0.55 for the ADP1173) The required inductor power is fairly low in this example, so the peak current can also be low. Assuming a peak current of 500 mA as a starting point, Equation 4 can be rearranged to recommend an inductor value: L= 2IOUT V OUT +V D DC V IN –V SW +V D The inductor value can now be calculated: –1.0 Ω × 23 µs 3V 1– e 100 µH = 616 mA 1.0 Ω L= Once the peak current is known, the inductor energy can be calculated from Equation 5: V IN(MIN ) –V SW –V OUT × tON I PEAK (7) where tON = switch ON time (23 µs) If the input voltage will vary (such as an application that must operate from a 12 V to 24 V source) an RLIM resistor should be selected from Figure 5. The RLIM resistor will keep switch current constant as the input voltage rises. Note that there are separate RLIM values for step-up and step-down modes of operation. 1 E L = (100 µH )× (616 mA)2 =19 µJ 2 The inductor energy of 19 µJ is greater than the PL/fOSC requirement of 13.5 µJ, so the 100 µH inductor will work in this application. By substituting other inductor values into the same equations, the optimum inductor value can be selected. –6– REV. 0 ADP1173 For example, assume that +5 V at 300 mA is required from a 12 V to +24 V input. Deriving the peak current from Equation 6 yields: I PEAK I PEAK = 2 × 300 mA 5 + 0.5 = 12 – 1.5 + 0.5 = 545 mA 0.55 The peak current can then be inserted into Equation 7 to calculate the inductor value: L= To avoid exceeding the maximum switch current when the input voltage is at +24 V, an RLIM resistor should be specified. Using the step-down curve of Figure 5, a value of 180 Ω will limit the switch current to 600 mA. Inductor Selection—Positive-to-Negative Converter The configuration for a positive-to-negative converter using the ADP1173 is shown in Figure 17. As with the step-up converter, all of the output power for the inverting circuit must be supplied by the inductor. The required inductor power is derived from the formula: P L = (|V OUT|+V D ) × ( IOUT ) (8) The ADP1173 power switch does not saturate in positive-tonegative mode. The voltage drop across the switch can be modeled as a 0.75 V base-emitter diode in series with a 0.65 Ω resistor. When the switch turns on, inductor current will rise at a rate determined by: _R't VL 1– e L R' where R' = 0.65 Ω + RL(DC) where VL = VIN – 0.75 V For example, assume that a –5 V output at 50 mA is to be generated from a +4.5 V to +5.5 V source. The power in the inductor is calculated from Equation 8: P L = (|−5V|+ 0.5V ) × (50 mA) = 275 mW During each switching cycle, the inductor must supply the following energy: P L 275 mW = =11.5 µJ f OSC 24 kHz –0.85 Ω × 23 µs 4.5V – 0.75V 220 µH 1– e = 375 mA 0.65 Ω + 0.2 Ω Once the peak current is known, the inductor energy can be calculated from Equation 5: 1 E L = (220 µH ) × (375 mA)2 =15.5 µJ 2 12 –1.5 – 5 × 23 µs = 232 µH 545 mA Since 232 µH is not a standard value, the next lower standard value of 220 µH would be specified. I L (t) = Using a standard inductor value of 220 µH, with 0.2 Ω dc resistance, will produce a peak switch current of: (9) The inductor energy of 15.5 µJ is greater than the PL/fOSC requirement of 11.5 µJ, so the 220 µH inductor will work in this application. The input voltage only varies between 4.5 V and 5.5 V in this example. Therefore, the peak current will not change enough to require an RLIM resistor and the ILIM pin can be connected directly to VIN. Care should be taken to ensure that the peak current does not exceed 650 mA. CAPACITOR SELECTION For optimum performance, the ADP1173’s output capacitor must be carefully selected. Choosing an inappropriate capacitor can result in low efficiency and/or high output ripple. Ordinary aluminum electrolytic capacitors are inexpensive, but often have poor Equivalent Series Resistance (ESR) and Equivalent Series Inductance (ESL). Low ESR aluminum capacitors, specifically designed for switch mode converter applications, are also available, and these are a better choice than general purpose devices. Even better performance can be achieved with tantalum capacitors, although their cost is higher. Very low values of ESR can be achieved by using OS-CON* capacitors (Sanyo Corporation, San Diego, CA). These devices are fairly small, available with tape-and-reel packaging, and have very low ESR. The effects of capacitor selection on output ripple are demonstrated in Figures 11, 12, and 13. These figures show the output of the same ADP1173 converter, which was evaluated with three different output capacitors. In each case, the peak switch current is 500 mA and the capacitor value is 100 µF. Figure 11 shows a Panasonic HF-series* radial aluminum electrolytic. When the switch turns off, the output voltage jumps by about 90 mV and then decays as the inductor discharges into the capacitor. The rise in voltage indicates an ESR of about 0.18 Ω. In Figure 12, the aluminum electrolytic has been replaced by a Sprague 593D-series* tantalum device. In this case the output jumps about 35 mV, which indicates an ESR of 0.07 Ω. Figure 13 shows an OS-CON SA series capacitor in the same circuit, and ESR is only 0.02 Ω. *All trademarks are properties of their respective holders. REV. 0 –7– ADP1173 DIODE SELECTION In specifying a diode, consideration must be given to speed, forward voltage drop and reverse leakage current. When the ADP1173 switch turns off, the diode must turn on rapidly if high efficiency is to be maintained. Schottky rectifiers, as well as fast signal diodes such as the 1N4148, are appropriate. The forward voltage of the diode represents power that is not delivered to the load, so VF must also be minimized. Again, Schottky diodes are recommended. Leakage current is especially important in low current applications, where the leakage can be a significant percentage of the total quiescent current. For most circuits, the 1N5818 is a suitable companion to the ADP1173. This diode has a VF of 0.5 V at 1 A, 4 µA to 10 µA leakage, and fast turn-on and turn-off times. A surface mount version, the MBRS130T3, is also available. For applications where the ADP1173 is “off” most of the time, such as when the load is intermittent, a silicon diode may provide higher overall efficiency due to lower leakage. For example, the 1N4933 has a 1 A capability, but with a leakage current of less than 1 µA. The higher forward voltage of the 1N4933 reduces efficiency when the ADP1173 delivers power, but the lower leakage may outweigh the reduction in efficiency. Figure 11. Aluminum Electrolytic For switch currents of 100 mA or less, a Schottky diode such as the BAT85 provides a VF of 0.8 V at 100 mA and leakage less than 1 µA. A similar device, the BAT54, is available in a SOT23 package. Even lower leakage, in the 1 nA to 5 nA range, can be obtained with a 1N4148 signal diode. General purpose rectifiers, such as the 1N4001, are not suitable for ADP1173 circuits. These devices, which have turn-on times of 10 µs or more, are too slow for switching power supply applications. Using such a diode “just to get started” will result in wasted time and effort. Even if an ADP1173 circuit appears to function with a 1N4001, the resulting performance will not be indicative of the circuit performance when the correct diode is used. Figure 12. Tantalum Electrolytic CIRCUIT OPERATION, STEP-UP (BOOST) MODE In boost mode, the ADP1173 produces an output voltage that is higher than the input voltage. For example, +12 V can be generated from a +5 V logic power supply or +5 V can be derived from two alkaline cells (+3 V). Figure 16 shows an ADP1173 configured for step-up operation. The collector of the internal power switch is connected to the output side of the inductor, while the emitter is connected to GND. When the switch turns on, pin SW1 is pulled near ground. This action forces a voltage across L1 equal to VIN–VCE(SAT), and current begins to flow through L1. This current reaches a final value (ignoring second-order effects) of: Figure 13. OS-CON Capacitor If low output ripple is important, the user should consider the ADP3000. This device switches at 400 kHz, and the higher switching frequency simplifies the design of the output filter. Consult the ADP3000 data sheet for additional details. All potential current paths must be considered when analyzing very low power applications, and this includes capacitor leakage current. OS-CON capacitors have leakage in the 5 µA to 10 µA range, which will reduce efficiency when the load is also in the microampere range. Tantalum capacitors, with typical leakage in the 1 µA to 5 µA range, are recommended for very low power applications. I PEAK ≅ V IN –V CE(SAT ) × 23 µs L where 23 µs is the ADP1173 switch’s “on” time. –8– REV. 0 ADP1173 L1 D1 VOUT VIN R3* R1 1 2 ILIM VIN SW1 3 + ADP1173 GND SW2 5 4 FB C1 8 R2 * = OPTIONAL Figure 14. Step-Up Mode Operation When the switch turns off, the magnetic field collapses. The polarity across the inductor changes, current begins to flow through D1 into the load and the output voltage is driven above the input voltage. The output voltage is fed back to the ADP1173 via resistors R1 and R2. When the voltage at pin FB falls below 1.245 V, SW1 turns “on” again and the cycle repeats. The output voltage is therefore set by the formula: R1 V OUT =1.245 V × 1+ R2 The circuit of Figure 14 shows a direct current path from VIN to VOUT, via the inductor and D1. Therefore, the boost converter is not protected if the output is short circuited to ground. When the switch turns off, the magnetic field collapses. The polarity across the inductor changes and the switch side of the inductor is driven below ground. Schottky diode D1 then turns on and current flows into the load. Notice that the Absolute Maximum Rating for the ADP1173’s SW2 pin is 0.5 V below ground. To avoid exceeding this limit, D1 must be a Schottky diode. Using a silicon diode in this application will generate forward voltages above 0.5 V, which will cause potentially damaging power dissipation within the ADP1173. The output voltage of the buck regulator is fed back to the ADP1173’s FB pin by resistors R1 and R2. When the voltage at pin FB falls below 1.245 V, the internal power switch turns “on” again and the cycle repeats. The output voltage is set by the formula: R1 V OUT =1.245 V × 1+ R2 When operating the ADP1173 in step-down mode, the output voltage is impressed across the internal power switch’s emitterbase junction when the switch is off. To protect the switch, the output voltage should be limited to 6.2 V or less. If a higher output voltage is required, a Schottky diode should be placed in series with SW2, as shown in Figure 16. If high output current is required in a step-down converter, the ADP1111 or ADP3000 should be considered. These devices offer higher frequency operation, which reduces inductor size, and an external pass transistor can be added to reduce RON of the switch. CIRCUIT OPERATION, STEP-DOWN (BUCK) MODE VIN RLIM 100Ω The ADP1173’s step-down mode is used to produce an output voltage lower than the input voltage. For example, the output of four NiCd cells (+4.8 V) can be converted to a +3.3 V logic supply. C2 I PEAK VIN R3 100Ω C2 1 2 3 ILIM VIN SW1 FB 8 ADP1173 GND SW2 4 VOUT + D1 1N5818 FB 8 ADP1173 GND 1N5818 L1 SW2 4 VOUT + 5 D1 1N5818 C1 R1 R2 Figure 16. Step-Down Mode, VOUT > 6.2 V C1 R1 R2 The ADP1173 can convert a positive input voltage to a negative output voltage, as shown in Figure 17. This circuit is essentially identical to the step-down application of Figure 15, except that the “output” side of the inductor is connected to power ground. When the ADP1173’s internal power switch turns off, current flowing in the inductor forces the output (–VOUT) to a negative potential. The ADP1173 will continue to turn the switch on Figure 15. Step-Down Mode Operation REV. 0 3 POSITIVE-TO-NEGATIVE CONVERSION L1 5 2 If the input voltage to the ADP1173 varies over a wide range, a current limiting resistor at Pin 1 may be required. If a particular circuit requires high peak inductor current with minimum input supply voltage, the peak current may exceed the switch maximum rating and/or saturate the inductor when the supply voltage is at the maximum value. See the Limiting the Switch Current section of this data sheet for specific recommendations. where 23 µs is the ADP1173 switch’s “on” time. + 1 ILIM VIN SW1 A typical configuration for step-down operation of the ADP1173 is shown in Figure 15. In this case, the collector of the internal power switch is connected to VIN and the emitter drives the inductor. When the switch turns on, SW2 is pulled up toward VIN. This forces a voltage across L1 equal to (VIN–VCE) – VOUT, and causes current to flow in L1. This current reaches a final value of: V –V CE –V OUT ≅ IN × 23 µs L + –9– ADP1173 until its FB pin is 1.245 V above its GND pin, so the output voltage is determined by the formula: LIMITING THE SWITCH CURRENT The ADP1173’s RLIM pin permits the switch current to be limited with a single resistor. This current limiting action occurs on a pulse by pulse basis. This feature allows the input voltage to vary over a wide range, without saturating the inductor or exceeding the maximum switch rating. For example, a particular design may require peak switch current of 800 mA with a 2.0 V input. If VIN rises to 4 V, however, the switch current will exceed 1.6 A. The ADP1173 limits switch current to 1.5 A and thereby protects the switch, but increases the output ripple. Selecting the proper resistor will limit the switch current to 800 mA, even if VIN increases. The relationship between RLIM and maximum switch current is shown in Figures 4 and 5. R1 =1.245 V × 1+ R2 –V OUT +VIN R3 C2 + 2 1 3 ILIM VIN SW1 FB 8 ADP1173 L1 SW2 4 GND + 5 R1 C1 D1 1N5818 The ILIM feature is also valuable for controlling inductor current when the ADP1173 goes into continuous-conduction mode. This occurs in the step-up mode when the following condition is met: R2 –VOUT V OUT +V DIODE 1 < V IN –V SW 1– DC Figure 17. A Positive-to-Negative Converter The design criteria for the step-down application also apply to the positive-to-negative converter. The output voltage should be limited to |6.2 V|, unless a diode is inserted in series with the SW2 Pin (see Figure 16). Also, D1 must again be a Schottky diode to prevent excessive power dissipation in the ADP1173. NEGATIVE-TO-POSITIVE CONVERSION The circuit of Figure 18 converts a negative input voltage to a positive output voltage. Operation of this circuit configuration is similar to the step-up topology of Figure 14, except that the current through feedback resistor R1 is level-shifted below ground by a PNP transistor. The voltage across R1 is (VOUT –VBEQ1). However, diode D2 level-shifts the base of Q1 about 0.6 V below ground, thereby cancelling the VBE of Q1. The addition of D2 also reduces the circuit’s output voltage sensitivity to temperature, which otherwise would be dominated by the –2 mV/°C VBE contribution of Q1. The output voltage for this circuit is determined by the formula: where DC is the ADP1173’s duty cycle. When this relationship exists, the inductor current does not go all the way to zero during the time the switch is OFF. When the switch turns on for the next cycle, the inductor current begins to ramp up from the residual level. If the switch ON time remains constant, the inductor current will increase to a high level (see Figure 19). This increases output ripple, and can require a larger inductor and capacitor. By controlling switch current with the ILIM resistor, output ripple current can be maintained at the design values. Figure 20 illustrates the action of the ILIM circuit. R1 V OUT = 1.245 V × R2 Unlike the positive step-up converter, the negative-to-positive converter’s output voltage can be either higher or lower than the input voltage. L1 + RLIM C2 + 1N5818 D1 R1 1 2 ILIM VIN SW1 3 Q1 2N3906 ADP1173 NEGATIVE INPUT 7 5 4 CL 1N4148 D2 10kΩ FB 8 AO SET GND SW2 6 Figure 19. (ILIM Operation, RLIM = 0 Ω) POSITIVE OUTPUT R2 NC NC Figure 18. A Negative-to-Positive Converter Figure 20. (ILIM Operation, RLIM = 240 Ω) –10– REV. 0 ADP1173 The internal structure of the ILIM circuit is shown in Figure 21. Q1 is the ADP1173’s internal power switch, which is paralleled by sense transistor Q2. The relative sizes of Q1 and Q2 are scaled so that IQ2 is 0.5% of IQ1. Current flows to Q2 through an internal 80 Ω resistor and through the RLIM resistor. These two resistors parallel the base-emitter junction of the oscillatordisable transistor, Q3. When the voltage across R1 and RLIM exceeds 0.6 V, Q3 turns on and terminates the output pulse. If only the 80 Ω internal resistor is used (i.e., the ILIM pin is connected directly to VIN), the maximum switch current will be 1.5 A. Figures 4 and 5 gives RLIM values for lower current-limit values. RLIM (EXTERNAL) VIN 80Ω (INTERNAL) SW1 Q3 VBAT OSCILLATOR 7 100kΩ VIN 1.245V REF SET AO TO PROCESSOR 6 GND R2 5 R1 = VLB –1.245V 12.5µA VLB = BATTERY TRIP POINT R2 = 100kΩ Figure 22. Setting the Low Battery Detector Trip Point R1 = DRIVER Q2 ADP1173 R1 Figure 22 shows the gain block configured as a low battery monitor. Resistors R1 and R2 should be set to high values to reduce quiescent current, but not so high that bias current in the SET input causes large errors. A value of 100 kΩ for R2 is a good compromise. The value for R1 is then calculated from the formula: ILIM R1 +5V 2 Q1 SW2 Figure 21. Current Limit Operation V LOBATT − 1.245 V 1.245 V R2 where VLOBATT is the desired low battery trip point. Since the gain block output is an open-collector NPN, a pull-up resistor should be connected to the positive logic power supply. The delay through the current limiting circuit is approximately 2 µs. If the switch ON time is reduced to less than 4 µs, accuracy of the current trip-point is reduced. Attempting to program a switch ON time of 2 µs or less will produce spurious responses in the switch ON time. However, the ADP1173 will still provide a properly regulated output voltage. 5V 2 ADP1173 R1 VBAT 7 47kΩ VIN 1.245mV REF SET AO 6 TO PROCESSOR GND R2 5 PROGRAMMING THE GAIN BLOCK The gain block of the ADP1173 can be used as a low-battery detector, error amplifier or linear post regulator. The gain block consists of an op amp with PNP inputs and an open-collector NPN output. The inverting input is internally connected to the ADP1173’s 1.245 V reference, while the noninverting input is available at the SET pin. The NPN output transistor will sink about 100 µA. REV. 0 R3 1.6MΩ Figure 23. Adding Hysteresis to the Low Battery Detector –11– ADP1173 Typical Circuit Applications L1* 68µH 100Ω 1N4148 R1 100Ω ILIM 2 x 1.5V CELLS 2.21MΩ 1% 2 1 9V BATTERY VIN SW1 3 ADP1173 1N5818 1N5818 4 118kΩ 1% 22µF *L1 = GOWANDA GA10-682K COILTRONICS CTX68-4 FOR 5V INPUT CHANGE R1 TO 47Ω CONVERTER WILL DELIVER –22V AT 40mA SW1 3 SENSE 8 SW2 5 GND SW2 4 VIN GND FB 8 5 2 ILIM ADP1173-5 0.1µF 4.7µF 1 1N5818 220kΩ –22V OUTPUT 7mA AT 2.0V INPUT 70% EFFICIENCY L1* 47µH 100µF + 5V OUTPUT 150mA AT 9V INPUT 50mA AT 6.5V INPUT *L1 = GOWANDA GA10-472K COILTRONICS CTX50-1 FOR HIGHER OUTPUT CURRENTS SEE ADP1073 DATASHEET Figure 27. 9 V to 5 V Converter Figure 24. 3 V–22 V LCD Bias Generator +VIN 12V-28V L1* 82µH ILIM 2 x 1.5V CELLS VIN SW1 3 SW2 5 4 1N5818 SENSE 8 + 5 5V OUTPUT 150mA AT 3V INPUT 60mA AT 2V INPUT SW1 3 SENSE 8 SW2 4 1N5818 100µF L1* 220µH 100µF + 5V OUTPUT 300mA *L1 = GOWANDA GA10-223K *L1 = GOWANDA GA10-822K Figure 28. +20 V to 5 V Step-Down Converter Figure 25. 3 V to 5 V Step-Up Converter +VIN 5V INPUT 2 VIN GND ADP1173-5 GND 1 ILIM ADP1173-5 2 1 100Ω + 22µF 100Ω 1 2 ILIM VIN SW1 3 ADP1173-5 GND 5 SENSE 8 SW2 4 L1* 100µH + 1N5818 100µF *L1 = GOWANDA GA10-103K COILTRONICS CTX100-1 –5V OUTPUT 75mA Figure 26. +5 V to –5 V Converter –12– REV. 0 ADP1173 44mH L1* 500µH ~ + 48V DC 44mH MUR110 + ~ 47µF 100V + 3.6MΩ – 10kΩ 2N5400 VN2222L 12V IRF530 15V 10nF *L1 = CTX110077 IQ = 120µA 220µF 10V 100Ω VIN ILIM 1N965B 1N4148 2 1 10µF 16V + +5V 100mA 390kΩ SW1 3 ADP1173 GND SW2 5 4 FB 8 110kΩ Figure 29. Telecom Supply L1* 100µH 1N5818 SI9405DY VOUT = 5V AT 100mA AT VIN = 2.6V 56Ω + 470µF 4 x NICAD OR ALKALINE CELLS 7 1 2 ILIM VIN SET 470kΩ ADP1173 GND SW2 5 4 75k SW1 3 + AO 6 470µF FB 8 470µF + 240Ω 24kΩ *L1 = GOWANDA GA20-103K COILTRONICS CTX100-4 VIN = 2.6V TO 7.2V Figure 30. 5 V to 5 V Step-Up or Step-Down Converter L1* 20µH, 5A 100kΩ 47kΩ 100kΩ 470µF + 2N3906 6 AO 7 SET 2.2MΩ 2 x NICAD 1 2 ILIM VIN 1N5820 220Ω 100Ω 2N4403 SW1 3 ADP1173 +5V OUTPUT 200mA LOCKOUT AT 1.85V INPUT 301kΩ† FB 8 GND SW2 5 4 5Ω 100kΩ + MJE200 100kΩ† 470µF 47Ω *L1 = COILTRONICS CTX-20-5-52 †1% METAL FILM Figure 31. 2 V to 5 V at 200 mA Step-Up Converter with Undervoltage Lockout REV. 0 –13– ADP1173 0.22Ω VIN 7V-24V 1N5818 18V 1W 1N5820 2kΩ 2N3904 2 1 ILIM L1* 25µH, 2A MTM20P08 + 51Ω 470µF VIN SW1 3 100Ω 1/2W ADP1173 GND SW2 5 4 1N4148 VIN 200kΩ –VOUT = –5.13*VC 39kΩ VC (0V TO +5V) OP196 FB 8 *L1 = GOWANDA GT10-100 EFFICIENCY ≥ 80% FOR 10mA ≤ ILOAD ≤ 500mA STANDBY IQ ≤ 150µA Figure 32. Voltage Controlled Positive-to-Negative Converter 0.22Ω VIN 7V-24V MTM20P08 1N5818 18V 1W ILIM 1N5820 2kΩ 2N3904 2 1 L1* 25µH, 2A 5V 500mA + 470µF 51Ω VIN SW1 3 100Ω 1/2W ADP1173 GND SW2 5 4 1N4148 121kΩ FB 8 OPERATE STANDBY 40.2kΩ *L1 = GOWANDA GT10-100 EFFICIENCY ≥ 80% FOR 10mA ≤ ILOAD ≤ 500mA STANDBY IQ ≤ 150µA Figure 33. High Power, Low Quiescent Current Step-Down Converter –14– REV. 0 ADP1173 OUTLINE DIMENSIONS Dimensions shown in inches and (mm). 8-Lead Plastic DIP (N-8) 0.430 (10.92) 0.348 (8.84) 8 5 0.280 (7.11) 0.240 (6.10) 1 4 0.060 (1.52) 0.015 (0.38) PIN 1 0.210 (5.33) MAX 0.325 (8.25) 0.300 (7.62) 0.195 (4.95) 0.115 (2.93) 0.130 (3.30) MIN 0.160 (4.06) 0.115 (2.93) 0.022 (0.558) 0.100 0.070 (1.77) 0.014 (0.356) (2.54) 0.045 (1.15) BSC 0.015 (0.381) 0.008 (0.204) SEATING PLANE 8-Lead Small Outline Package (SO-8) 0.1968 (5.00) 0.1890 (4.80) 0.1574 (4.00) 0.1497 (3.80) PIN 1 0.0098 (0.25) 0.0040 (0.10) SEATING PLANE REV. 0 8 5 1 4 0.2440 (6.20) 0.2284 (5.80) 0.0688 (1.75) 0.0532 (1.35) 0.0500 0.0192 (0.49) (1.27) 0.0138 (0.35) BSC 0.0196 (0.50) x 45° 0.0099 (0.25) 0.0098 (0.25) 0.0075 (0.19) –15– 8° 0° 0.0500 (1.27) 0.0160 (0.41) –16– PRINTED IN U.S.A. C2965–12–1/97