ADP1108AR-33

ADP1108 AD | Alldatasheet

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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. a Micropower DC-DC Converter Adjustable and Fixed 3.3 V, 5 V, 12 V ADP1108 FUNCTIONAL BLOCK DIAGRAMS SET VIN GAIN BLOCK/ ERROR AMP COMPARATOR SW2FBGND SW1 AO ILIM OSCILLATOR DRIVER 1.245V REFERENCE ADP1108 SET VIN GAIN BLOCK/ ERROR AMP COMPARATOR SW2 SENSEGND SW1 AO ILIM OSCILLATOR DRIVER 1.245V REFERENCE ADP1108-3.3 ADP1108-5 ADP1108-12 753kΩ ADP1108-3.3: R1 = 456kΩ ADP1108-5: R1 = 250kΩ ADP1108-12: R1 = 87.4kΩ GENERAL DESCRIPTION The ADP1108 is a highly versatile micropower switch-mode dc-dc converter that operates from an input voltage supply as low as 2.0 V and typically starts up from 1.8 V. The ADP1108 can be programmed into a step-up or step-down dc-to-dc converter with only three external components. The fixed outputs are 3.3 V, 5 V and 12 V. An adjustable version is also available. In step-up mode, supply voltage range is 2.0 V to 12 V, and 30 V in step-down mode. The ADP1108 can deliver 150 mA at 5 V from a 2 AA cell input and 300 mA at 5 V from a 9 V input in step-down mode. Switch current limit can be programmed with a single resistor. For battery operated and power conscious applications, the ADP1108 offers a very low power consumption of less than 110 µA. The auxiliary gain block available in ADP1108 can be used as a low battery detector, linear post regulator, under voltage lockout circuit or error amplifier.

FEATURES

Operates at Supply Voltages From 2.0 V to 30 V Consumes Only 110 mA Supply Current Step-Up or Step-Down Mode Operation Minimum External Components Required Low Battery Detector Comparator On-Chip User-Adjustable Current Limit Internal 1 A Power Switch Fixed or Adjustable Output Voltage Versions 8-Pin DIP or SO-8 Package

APPLICATIONS

Notebook/Palm Top Computers

3 V to 5 V, 5 V to 12 V Converters

9 V to 5 V, 12 V to 5 V Converters

Peripherals and Add-On Cards Battery Backup Supplies Cellular Telephones Portable Instruments Tel: 617/329-4700 World Wide Web Site: http://www.analog.com Fax: 617/326-8703 © Analog Devices, Inc., 1997

REV. 0–2– ADP1108–SPECIFICATIONS Parameter Symbol Conditions Min Typ Max Units QUIESCENT CURRENT I Q Switch Off 90 150 µA QUIESCENT CURRENT, I Q No Load, TA = +25°C BOOST MODE CONFIGURATION ADP1108-3.3 90 µA ADP1108-5 90 µA ADP1108-12 90 µA INPUT VOLTAGE V IN Step-Up Mode 2.0 12.6 V Step-Down Mode 30 V COMPARATOR TRIP POINT VOLTAGE ADP1108 1 1.20 1.245 1.30 V OUTPUT SENSE VOLTAGE V OUT ADP1108-3.32 3.13 3.3 3.46 V ADP1108-52 4.75 5.00 5.25 V ADP1108-122 11.4 12.0 12.6 V COMPARATOR HYSTERESIS ADP1108 5 12 mV OUTPUT HYSTERESIS ADP1108-3.3 13 30 mV ADP1108-5 20 55 mV ADP1108-12 50 100 mV OSCILLATOR FREQUENCY 14 19 25 kHz DUTY CYCLE Full Load 55 70 78 % SWITCH ON TIME t ON ILIM Tied to VIN 25 36 48 µs FEEDBACK PIN BIAS CURRENT VFB = 0 V 25 200 nA SET PIN BIAS CURRENT V SET = VREF 60 130 nA GAIN BLOCK OUTPUT LOW V OL ISINK = 100 µA, VSET = 1.00 V 0.15 0.4 V REFERENCE LINE REGULATION 2.0 V ≤ VIN ≤ 5 V 0.2 0.4 %/V 5 V ≤ VIN ≤ 30 V 0.02 0.075 %/V SWSAT VOLTAGE, STEP-UP MODE V SAT VIN = 3.0 V, ISW = 650 mA 0.5 0.75 V VIN = 5.0 V, ISW = 1 A, 0.8 1.00 V TA = +25°CV SWSAT VOLTAGE, SAT VIN = 12 V, ISW = 650 mA, TA = +25°C 1.1 1.5 V STEP-DOWN MODE 1.7 V GAIN BLOCK GAIN A V RL = 100K3 400 1000 V/V CURRENT LIMIT 220 Ω from ILIM to VIN, TA = +25°C 500 mA CURRENT LIMIT TEMPERATURE COEFFICIENT –0.3 %/ °C SWITCH OFF LEAKAGE CURRENT Measured at SW1 Pin, TA = +25°C1 1 0 µA MAXIMUM EXCURSION BELOW GND V SW2 1SW1 ≤ 10 µA, Switch Off TA = +25°C –400 –350 mV NOTES 1This specification guarantees that both the high and low trip points of the comparator fall within the 1.20 V to 1.30 V range. 2The output voltage waveform will exhibit a sawtooth shape due to the comparator hysteresis. The output voltage on the fixed out put versions will always be within the specified range. 3100 kΩ resistor connected between a 5 V source and the AO pin. All limits at temperature extremes are guaranteed via correlation using standard Quality Control methods. Specifications subject to change without notice. (08C to +708C, VIN = 3.0 V unless otherwise noted)

–3–REV. 0 ABSOLUTE MAXIMUM RATINGS* *Stresses above those listed under Absolute Maximum Ratings may cause perma- nent 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 rating conditions for extended periods may affect device reliability. ORDERING GUIDE Model Output Voltage Package* ADP1108AN ADJ N-8 ADP1108AR ADJ SO-8 ADP1108AN-3.3 3.3 V N-8 ADP1108AR-3.3 3.3 V SO-8 ADP1108AN-5 5 V N-8 ADP1108AR-5 5 V SO-8 ADP1108AN-12 12 V N-8 ADP1108AR-12 12 V SO-8 *N = Plastic DIP, SO = Small Outline Package. PIN CONFIGURATIONS 8-Lead Plastic DIP 8-Lead SOIC (N-8) (SO-8) TOP VIEW (Not to Scale) ADP1108 ILIM VIN SW1 SW2 FB (SENSE)* SET AO GND * FIXED VERSIONS TOP VIEW (Not to Scale) ADP1108 ILIM VIN SW1 SW2 FB (SENSE)* SET AO GND * 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 I LIM and VIN. Limiting the switch current to 400 mA is achieved by connecting a 220 Ω resistor. VIN Input Voltage. SW1 Collector of Power Transistor. For step-down configuration, connect to V IN. For step-up configuration, connect to an inductor/diode. SW2 Emitter of Power Transistor. For step-down configuration, connect to inductor/diode. For step-up configuration, connect to ground. Do not allow this pin to go 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 SET pin and negative input connected to 1.245 V reference. FB/SENSE On the ADP1108 (adjustable) version this pin is connected to the comparator input. On the ADP1108-3.3, ADP1108-5 and ADP1108-12, the pin goes directly to the internal application resistor that set output voltage. WARNING! ESD SENSITIVE DEVICE 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 ADP1108 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.

Figure 1. Saturation Voltage vs. ISWITCH Figure 4. Maximum Switch Current Figure 7. Oscillator Frequency vs. Figure 2. Switch ON Voltage vs. Figure 5. Supply Current vs. Switch

62 DUTY CYCLE – %

Figure 8. Duty Cycle vs. Temperature Figure 3. Maximum Switch Current Figure 6. Quiescent Current vs. Figure 9. Switch ON Time vs.

–6– REV. 0 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, step- down or inverting). 3. Calculate the inductor value, using the equations in the fol- lowing sections. Inductor Selection—Step-Up Converter In a step-up or boost converter (Figure 15), the inductor must store enough power to make up the difference between the input voltage and the output voltage. The inductor power is calculated from the equation: PL = VOUT + VD − VIN MIN()() × IOUT() (Equation 1) where VD is the diode forward voltage ( ≈ 0.5 V for a 1N5818 Schottky). Energy is only stored in the inductor while the ADP1108 switch is ON, so the energy stored in the inductor on each switching cycle must be equal to or greater than: PL fOSC (Equation 2) in order for the ADP1108 to regulate the output voltage. When the internal power switch turns ON, current flow in the inductor increases at the rate of: IL (t) = VIN R© 1− e ±R©t L  (Equation 3) where L is in henrys and R9 is the sum of the switch equivalent resistance (typically 0.8 Ω at +25°C) and the dc resistance of the inductor. If the voltage drop across the switch is small compared to V IN, a simpler equation can be used: IL(t) = VIN L t (Equation 4) Replacing t in the above equation with the ON time of the ADP1108 (36 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: EL = 1

2 L × I2

PEAK (Equation 5) As previously mentioned, EL must be greater than PL/fOSC so the ADP1108 can deliver the necessary power to the load. For best efficiency, peak current should be limited to 1 A or l ess. Higher switch currents will reduce efficiency because of increased satura- tion 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. In practice, the inductor value is easily selected using the equations above. For example, consider a supply that will generate 12 V at 30 mA from a 3 V battery, assuming a 2 V end-of-life voltage. The inductor power required is from Equation 1: PL = 12V + 0.5V ±2 V() × 30 mA() = 315 mW On each switching cycle, the inductor must supply: PL fOSC = 315 mW 19kHz = 16.6µ J 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 = VIN IL(MAX ) t = 2V 500 mA 36 µs = 144 µH Substituting a standard inductor value of 100 µH with 0.2 Ω dc resistance, will produce a peak switch current of: IPEAK = 2V 1. 0Ω 1± e ±1.0Ω× 36 µs 100 µH  = 605 mA Once the peak current is known, the inductor energy can be calculated from Equation 5: EL = 1 2 100 µH × 605 mA()  = 18.3µ J The inductor energy of 18.3 µJ is greater than the P L/fOSC requirement of 16.6 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. When selecting an inductor, the peak current must not exceed the maximum switch current of 1.5 A. If the calculated peak current is greater than 1.5 A, either the ADP3000 should be considered or an external power transistor can be used. The peak current must be evaluated for both minimum and maximum values of input voltage. If the switch current is high when V IN is at its minimum, the 1.5 A limit may be exceeded at the maximum value of VIN. In this case, the current limit feature of the ADP1108 can be used to limit switch current. Simply select a resistor (using Figure 3) 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. Note that the switch current limit feature does not protect the circuit if the output is shorted to ground. In this case, current is limited only by the dc resistance of the inductor and the forward voltage of the diode. Inductor Selection—Step-Down Converter The step-down mode of operation is shown in Figure 16. Unlike the step-up mode, the ADP1108’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 I LIM pin can be used to limit the maximum switch current. Higher switch current is possible by adding an external switching transistor, as shown in Figure 18. The first step in selecting the step-down inductor is to calculate the peak switch current as follows: IPEAK = 2 IOUT DC VOUT + VD VIN ±VSW + VD  (Equation 6)

–7–REV. 0 where: DC = duty cycle (0.7 for the ADP1108) 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 As previously mentioned, the switch voltage is higher in step- down mode than in step-up mode. V SW is a function of switch current and is therefore a function of V IN, L, time and VOUT. For most applications, a V SW value of 1.5 V is recommended. The inductor value can now be calculated: L =VIN(MIN) ±VSW ±VOUT IPEAK × tON (Equation 7) where: tON = switch ON time (36 µs) If the input voltage will vary (such as an application that must operate from a 9 V, 12 V or 15 V source), an R LIM resistor should be selected from Figure 4. The R LIM resistor will keep switch current constant as the input voltage rises. Note that there are separate R LIM values for step-up and step-down modes of operation. For example, assume that +5 V at 250 mA is required from a +9 V to +18 V source. Deriving the peak current from Equation 6 yields: IPEAK = 2 × 250 mA 0.7 5 + 0.5 9 − 1. 5+ 0.5    = 491 mA The peak current can than be inserted into Equation 7 to cal- culate the inductor value: L = 9±1 . 5±5 491 mA × 36 µs = 183 µH Since 183 µH is not a standard value, the next lower standard value of 150 µH would be specified. To avoid exceeding the maximum switch current when the in- put voltage is at +18 V, an R LIM resistor should be specified. Us- ing Figure 4, a value of 160 Ω will limit the switch current to 500 mA. Inductor Selection—Positive-to-Negative Converter The configuration for a positive-to-negative converter using the ADP1108 is shown in Figure 19. 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: PL |VOUT|+ VD() × IOUT() (Equation 8) The ADP1108 power switch does not saturate in positive-to- negative mode. The voltage drop across the switch can be mod- eled 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: IL (t) = VL R© 1− e ±R©t L  (Equation 9) where: R' = 0.65 Ω + RL (DC) VL = VIN – 0.75 V For example, assume that a –5 V output at 100 mA is to be gen- erated from a +4.5 V to +5.5 V source. The power in the induc- tor is calculated from Equation 8: During each switching cycle, the inductor must supply the fol- lowing energy: PL fOSC = 550 mW 19kHz = 28.9µ J Using a standard inductor value of 220 µH with 0.3 Ω dc resis- tance will produce a peak switch current of: IPEAK = 4.5V ±0 . 7 5V 0.65 Ω+ 0.3 Ω 1− e ±0.95Ω× 36 µs 220 µH  = 568 mA Once the peak current is known, the inductor energy can be cal- culated from Equation 9: EL = 1 2 220 µH × 568 mA()  = 35.5µ J The inductor energy of 35.5 µJ is greater than the P L/fOSC re- quirement of 28.9 µJ, so the 220 µH inductor will work in this application. To avoid exceeding the maximum switch current when the in- put voltage is at +5.5 V, an R LIM resistor should be specified. Referring to Figure 4, a value of 150 V is appropriate in this application. Capacitor Selection For optimum performance, the ADP1108’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 Equiva- lent 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 Corpora- tion, 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 demon- strated in Figures 12, 13, and 14. These figures show the output of the same ADP1108 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 12 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 ca- pacitor. The rise in voltage indicates an ESR of about 0.18 V. In Figure 13, 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 V. Figure 14 shows an OS-CON SA series capacitor in the same circuit, and ESR is only 0.02 V. *All trademarks are the property of their respective holders.

–12– REV. 0 OUTLINE DIMENSIONS Dimensions shown in inches and (mm). 8-Lead Plastic DIP (N-8) 0.430 (10.92) 0.348 (8.84) 0.280 (7.11) 0.240 (6.10) PIN 1 SEATING PLANE0.022 (0.558) 0.014 (0.356) 0.060 (1.52) 0.015 (0.38) 0.210 (5.33) MAX 0.130 (3.30) MIN 0.070 (1.77) 0.045 (1.15) 0.100 (2.54) BSC 0.160 (4.06) 0.115 (2.93) 0.325 (8.25) 0.300 (7.62) 0.015 (0.381) 0.008 (0.204) 0.195 (4.95) 0.115 (2.93) 8-Lead SOIC (SO-8) 0.1968 (5.00) 0.1890 (4.80) 8 5 0.2440 (6.20) 0.2284 (5.80) PIN 1 0.1574 (4.00) 0.1497 (3.80) 0.0688 (1.75) 0.0532 (1.35)SEATING PLANE 0.0098 (0.25) 0.0040 (0.10) 0.0192 (0.49) 0.0138 (0.35) 0.0500 (1.27) BSC 0.0098 (0.25) 0.0075 (0.19) 0.0500 (1.27) 0.0160 (0.41) 0.0196 (0.50) 0.0099 (0.25)x 45° C2992–12–2/97PRINTED IN U.S.A.