Low-Supply Current, Step-Up DC-DC Converters with True Shutdown MAX1795/MAX1796/ MAX1797. General Description. Features. Ordering Information

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1 General Description The // are high-efficiency, step-up DC-DC converters intended for small portable hand-held devices. These devices feature Maxim s True Shutdown circuitry, which fully disconnects the output from the input in shutdown, improves efficiency, and eliminates costly external components. All three devices also feature Maxim s proprietary LX-damping circuitry for reduced EMI in noise-sensitive applications. For additional in-system flexibility, a battery monitoring comparator (LBI/LBO) remains active even when the DC-DC converter is in shutdown. The input voltage range is +.7 to, where can be set from +2 to Startup is guaranteed from The // have a preset, pin-selectable 5 or 3.3 output. The output can also be adjusted to other voltages, using two external resistors. The three devices differ only in their current limits, allowing optimization of external components for different loads: The,, and have current limits of.25a,.5a, and 1A, respectively. All devices are packaged in a compact, 8-pin μmax package that is only 1.9mm tall and half the size of an 8-pin SO. Applications Portable Digital Audio Players PDAs/Palmtops Wireless Handsets Portable Terminals Pin Configuration Features > 95% Efficiency True-Shutdown Circuitry Output Disconnects from Input in Shutdown No External Schottky Diode Needed 25μA Quiescent Supply Current Low-Noise Antiringing Feature LBI/LBO Comparator Enabled in Shutdown 2μA Shutdown Current 8-Pin μmax Package Ordering Information PART TEMP RANGE PIN-PACKAGE EUA -4 C to +85 C 8 μmax EUA -4 C to +85 C 8 μmax EUA -4 C to +85 C 8 μmax Typical Operating Circuit TOP IEW IN.7 TO 5.5 LX LBI FB LBO SHDN µmax LX GND OFF ON LBI LBO SHDN GND FB True Shutdown is a trademark of Maxim Integrated Products ; Rev ; 12/

2 Absolute Maximum Ratings, LX, SHDN, LBI, LBO, to GND to +6 FB to ( +.3) I LX, I...±1.5A Output Short-Circuit Duration... 5s Continuous Power Dissipation 8-Pin μmax (derate 4.1mW/ C above +7 C)...33mW Operating Temperature Range C to +85 C Junction Temperature C Storage Temperature Range C to +15 C Lead Temperature (soldering, 1s)...+3 C Stresses beyond those listed under Absolute Maximum Ratings may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability. Electrical Characteristics ( = +2, = FB ( = +3.3), SHDN = LBI = GND, T A = C to +85 C, unless otherwise noted. Typical values are at T A = +25 C.) PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS Minimum Input oltage After startup.7 Operating oltage (Note 1) Startup oltage T A = +25 C, R L = 3kΩ Startup oltage Tempco -2.2 m/ C FB = Output oltage FB = GND Adjustable Output oltage Range Steady-State Output Current Feedback Set-Point oltage (Adjustable Mode) I = +2, FB = ( = +3.3) = +2, FB = GND ( = +5.) FB = +2 to Feedback Input Current I FB FB = na Internal NFET, PFET On-Resistance LX Switch Current Limit (NFET only) R DS(ON) = +3.3, I LX = 1mA NFET.17.3 PFET I LIM LX Leakage Current I LEAK LX = and +5.5, = µa Synchronous Rectifier Turn-Off Current Limit ma Ω A 25 ma Damping Switch On-Resistance R DAMP Ω Operating Current into (Note 2) FB = µa Maxim Integrated 2

3 Electrical Characteristics (continued) ( = +2, = FB ( = +3.3), SHDN = LBI = GND, T A = C to +85 C, unless otherwise noted. Typical values are at T A = +25 C.) PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS Operating Current into FB = +1.4, LBI = µa Shutdown Current into SHDN =, LBI = µa LX Switch MaxImum On-Time t ON FB = +1, if current limit not reached µs LX Switch Minimum Off-Time t OFF FB = µs = LBI Threshold oltage Falling LBI = LBI LBI Hysteresis 25 m LBI Input Current I LBI LBI = na LBO Low Output oltage Electrical Characteristics = LBI = +.975, sinking 2µA (5Ω typ) = LBI = +1.1, sinking 1µA (25Ω typ) LBO Off-Leakage Current LBO = na SHDN Input oltage IL IH.8 x ( = +2, = FB ( = +3.3), SHDN = LBI = GND, T A = -4 C to +85 C, unless otherwise noted.) (Note 3) x Shutdown Input Current SHDN = and na PARAMETER SYMBOL CONDITIONS MIN MAX UNITS Operating oltage Note FB = Output oltage FB = GND Adjustable Output oltage Range Steady-State Output Current (Note 1) Feedback Set-Point oltage (Adjustable Mode) I FB = ( = +3.3) FB = GND ( = +5.) FB = +2 to Feedback Input Current I FB FB = na ma Maxim Integrated 3

4 Electrical Characteristics (continued) ( = +2, = FB ( = +3.3), SHDN = LBI = GND, T A = -4 C to +85 C, unless otherwise noted.) (Note 3) Internal NFET, PFET On-Resistance PARAMETER SYMBOL CONDITIONS MIN MAX UNITS LX Switch Current Limit (NFET only) R DS(ON) = +3.3, I LX = 1mA NFET.3 PFET.45 I LIM LX Leakage Current I LEAK LX = and +5.5, = +5.5 µa Damping Switch On-Resistance R DAMP 1 4 Ω Operating Current into (Note 2) FB = µa Operating Current into FB = +1.4, LBI = +1 4 µa Shutdown Current into SHDN =, LBI = +1 4 µa LX Switch Maximum On-Time t ON FB = +1, if current limit not reached µs LX Switch Minimum Off-Time t OFF FB = µs = LBI Threshold oltage LBI = LBI LBI Input Current I LBI LBI = na LBO Low Output oltage = LBI = +.975, sinking 2µA (5Ω typ) = LBI = +1.1, sinking 1µA (25Ω typ) LBO Off-Leakage Current LBO = na SHDN Input oltage IL IH.8 x Note 1: Operating oltage: Since the regulator is bootstrapped to the output, once started it will operate down to a.7 input. Note 2: Device is bootstrapped (power to IC comes from ). This correlates directly with the actual battery supply current. Note 3: Specifications to -4 C are guaranteed by design, not production tested x Shutdown Input Current SHDN = and na Ω A Maxim Integrated 4

5 Typical Operating Characteristics (L = 22μH, C IN = 47μF, C = 47μF, T A = +25 C, unless otherwise noted.) EFFICIENCY vs. LOAD CURRENT (+5) = +3.6 = +2.4 = +1.2 /96/97 toc EFFICIENCY vs. LOAD CURRENT (+3.3) = +2.4 = +1.2 /96/97 toc EFFICIENCY vs. LOAD CURRENT (+5) = +3.6 = +2.4 = +1.2 /96/97 toc L = 1µH EFFICIENCY vs. LOAD CURRENT (+3.3) = +2.4 = +1.2 /96/97 toc EFFICIENCY vs. LOAD CURRENT (+5) = +3.6 = +2.4 = +1.2 /96/97 toc EFFICIENCY vs. LOAD CURRENT (+3.3) = +2.4 = +1.2 /96/97 toc ERY CURRENT (µa) NO-LOAD ERY CURRENT vs. INPUT OLTAGE = +3.3 = +5 /96/97 toc STARTUP OLTAGE vs. LOAD CURRENT = +3.3 /96/97 toc8 SHUTDOWN THRESHOLD () SHUTDOWN THRESHOLD vs. INPUT OLTAGE /96/97 toc OLTAGE () OLTAGE () Maxim Integrated 5

6 Typical Operating Characteristics (continued) (L = 22μH, C IN = 47μF, C = 47μF, T A = +25 C, unless otherwise noted.) LOW-ERY INPUT THRESHOLD () LOW-ERY INPUT THRESHOLD vs. INPUT OLTAGE INCREASING LBI DECREASING LBI /96/97 toc1 LOW-ERY INPUT THRESHOLD () LOW-ERY INPUT THRESHOLD vs. TEMPERATURE = +3.6 INCREASING LBI DECREASING LBI /96/97 toc MAXIMUM PUT CURRENT vs. INPUT OLTAGE = +3.3 = +5. /96/97 toc OLTAGE () TEMPERATURE ( C) OLTAGE () MAXIMUM PUT CURRENT vs. INPUT OLTAGE = +3.3 = +5. /96/97 toc MAXIMUM PUT CURRENT vs. INPUT OLTAGE = +3.3 = +5. /96/97 toc OLTAGE () OLTAGE () LEAKAGE CURRENT (A) LEAKAGE CURRENT vs. PUT OLTAGE SHDN = = +5 = +2.4 BIASED WITH EXTERNAL OLTAGE SOURCE PUT OLTAGE () /96/97 toc15 HEAY-LOAD SWITCHING WAEFORMS /96/97 toc16 IN = +3.6 = +5. I LOAD = 4mA 4.µs/div LX 5/div I INDUCTOR 5mA/div (AC-COUPLED) 1m/div Maxim Integrated 6

7 Typical Operating Characteristics (continued) (L = 22μH, C IN = 47μF, C = 47μF, T A = +25 C, unless otherwise noted.) LIGHT-LOAD SWITCHING WAEFORMS /96/97 toc17 LINE-TRANSIENT RESPONSE /96/97 toc18 LX 5/div +2.7 TO +3 I INDUCTOR 5mA/div (AC-COUPLED) 1m/div (AC-COUPLED) 2m/div = +3.6 = +5. I LOAD = 4mA 2µs/div 1µs/div = +2.7 TO +3 = +5. NO LOAD LOAD-TRANSIENT RESPONSE /96/97 toc19 STARTUP-SHUTDOWN WAEFORMS /96/97 toc2 I 1mA/div SHDN 5/div 2/div 1m/div I INDUCTOR 5mA/div 4µs/div = +2.4 = +3.3 I LOAD = TO 325mA = +2.4 = +5. I LOAD = 2mA 2ms/div Maxim Integrated 7

8 Pin Description PIN NAME FUNCTION 1 LBI 2 FB 3 LBO 4 SHDN 5 GND Ground Low-Battery Comparator Input. Internally set to trip at This function remains operational in shutdown. Dual-Mode Feedback Input. Connect to GND for preset 5. output. Connect to for preset 3.3 output. Connect a resistive voltage-divider from to GND to adjust the output voltage from 2 to 5.5. Low-Battery Comparator Output, Open-Drain Output. LBO is high impedance when LBI <.85. This function remains operational in shutdown. Shutdown Input. If SHDN is high, the device is in shutdown mode, is high impedance, and LBI/LBO are still operational. Connect shutdown to GND for normal operation. 6 LX Inductor Connection 7 Power Output. provides bootstrap power to the IC. 8 Battery Input and Damping Switch Connection Detailed Description The // compact step-up DC-DC converters start up with voltages as low as.85 and operate with an input voltage down to +.7. Consuming only 25μA of quiescent current, these devices have an internal synchronous rectifier that reduces cost by eliminating the need for an external diode and improves overall efficiency by minimizing losses in the circuit (see Synchronous Rectification section for details). The internal N-channel MOSFET power switch resistance is typically.17ω, which minimizes losses. The LX switch current limits of the // are.25a,.5a, and 1A, respectively. All three devices offer Maxim s proprietary True Shutdown circuitry, which disconnects the output from the input in shutdown and puts the output in a high impedance state. These devices also feature Maxim s proprietary LX-damping circuitry, which reduces EMI in noise-sensitive applications. For additional in-system flexibility, the LBI/LBO comparator remains active in shutdown. Figure 1 is a typical application circuit. Control Scheme A unique minimum-off-time, current-limited control scheme is the key to the //s low operating current and high efficiency over a wide load range. The architecture combines the high output power and efficiency of a pulse-width-modulation (PWM) device with the ultra-low quiescent current of a traditional IN IN 1M SHDN LBO LBI GND *SEE TABLE 1 FOR COMPONENT ALUES. Figure 1. Typical Application Circuit pulse-skipping controller (Figure 2). Switching frequency depends upon the load current and input voltage, and can range up to 5kHz. Unlike conventional pulse-skipping DC-DC converters (where ripple amplitude varies with input voltage), ripple in these devices does not exceed the product of the switch current limit and the filter-capacitor equivalent series resistance (ESR). LX C * FB 22µH = 3.3 Dual Mode is a trademark of Maxim Integrated Products. Maxim Integrated 8

9 R1 1M SHDN LBO LBI + _ Q S ZERO- CROSSING AMPLIFIER.85 R S R Q BODY DIODE CONTROL 22µH TIMER BLOCK 47F S Q LX START TON MAX TOFF MAX R R2 R3 FB FB SELECT REFERENCE ERROR AMPLIFIER CURRENT-LIMIT AMPLIFIER GND Figure 2. Functional Diagram Synchronous Rectification The internal synchronous rectifier eliminates the need for an external Schottky diode, reducing cost and board space. During the cycle off-time, the P-channel MOSFET turns on and shunts the MOSFET body diode. As a result, the synchronous rectifier significantly improves efficiency without the addition of an external component. Conversion efficiency can be as high as 95%, as shown in the Typical Operating Characteristics section. Shutdown The device enters shutdown when SHDN is high, reducing supply current to less than 2μA. During shutdown, the synchronous rectifier disconnects the output from the input, eliminating the DC conduction path that normally exists with traditional boost converters in shutdown mode. In shutdown, becomes a high- impedance node. The LBI/LBO comparator remains active in shutdown. As shown in Figure 1, the // can be automatically shut down when the input voltage drops below a preset threshold by connecting LBO to SHDN (see the Low-Battery Detection section). /Damping Switch The // each contain an internal damping switch to minimize ringing at LX. The damping switch connects a resistor across the inductor when the inductor s energy is depleted (Figure 3). Normally, when the energy in the inductor is insufficient to supply current to the output, the capacitance and inductance at LX form a resonant circuit that causes ringing. The ringing continues until the energy is dissipated through the series resistance of the inductor. The damping switch supplies a Maxim Integrated 9

10 IN path to quickly dissipate this energy, minimizing the ringing at LX. Damping LX ringing does not reduce ripple, but does reduce EMI (Figure 3, Figure 4, and Figure 5). R1 2Ω DAMPING SWITCH 22µH Setting the Output oltage can be set to 3.3 or 5. by connecting the FB pin to GND (5) or (3.3). To adjust the output voltage, connect a resistive voltage-divider from to FB to GND (Figure 6). Choose a value less than 25kΩ for R2. LX IN Figure 3. Simplified Diagram of Inductor Damping Switch LX LX 1/div R3 R4 LBI SHDN LBO GND FB 1M R1 R2 PUT 2 TO 5.5 LOW-ERY PUT Figure 6. Setting an Adjustable Output 2µs/div Figure 4. LX Ringing for Conventional Step-Up Converter (without Damping Switch) 2µs/div Figure 5. LX Waveform with Damping Switch LX 1/div Use the following equation to calculate R1: R1 = R2 [( / FB ) - 1] where FB = , and can range from +2 to Low-Battery Detection The // each contain an onchip comparator for low-battery detection. If the voltage at LBI is above.85, LBO (an open-drain output) sinks current to GND. If the voltage at LBI is below.85, LBO goes high impedance. The LBI/LBO function remains active even when the part is in shutdown. Connect a resistive voltage-divider to LBI from to GND. The low-battery monitor threshold is set by two resistors, R3 and R4 (Figure 6). Since the LBI bias current is typically 2nA, large resistor values (R4 up to 25kΩ) can be used to minimize loading of the input supply. Calculate R3 using the following equation: R3 = R4[( TRIP /.85) - 1] Maxim Integrated 1

11 TRIP is the input voltage where the low-battery detector output goes high impedance. For single-cell applications, LBI may be connected to the battery. When <1.>, the LBI threshold increases to.925 (see the Typical Operating Characteristics section). Connect a pullup resistor of 1kΩ or greater from LBO to for a logic output. LBO is an open-drain output and can be pulled as high as 6 regardless of the voltage at. When LBI is below the threshold, the LBO output is high impedance. If the low-battery comparator is not used, ground LBI and LBO. Applications Information Inductor Selection An inductor value of 22μH performs well in most applications. The // will also work with inductors in the 1μH to 47μH range. Smaller inductance values typically offer a smaller physical size for a given series resistance, allowing the smallest overall circuit dimensions, but have lower output current capability. Circuits using larger inductance values exhibit higher output current capability, but are physically larger for the same series resistance and current rating. The inductor s incremental saturation current rating should be greater than the peak switch-current limit, which is.25a for the,.5a for the, and 1A for the. However, it is generally acceptable to bias the inductor into saturation by as much as 2% although this will slightly reduce efficiency. Table 1 lists some suggested components for typical applications. The inductor s DC resistance significantly affects efficiency. Calculate the maximum output current (I (MAX) ) as follows, using inductor ripple current (I RIP ) and duty cycle (D): + I LIM (RPFET + L ESR ) IRIP = L (RPFET + L ESR ) + toff 2 I RIP + I LIM (RPFET + L ESR ) 2 D = I RIP + I LIM (RPFET RNFET + L ESR ) 2 and IRIP I(MAX) = ILIM + 2 where: I RIP = Inductor ripple current (A) = Output voltage () I LIM = Device current limit (.25A,.5A, or 1A) R PFET = On-resistance of P-channel MOSFET (Ω) (typ.27ω) L ESR = ESR of Inductor (Ω) (typ.95ω) = Input voltage () L = Inductor value in μh t OFF = LX switch s off-time (μs) (typ 1μs) D = Duty cycle R NFET = On-resistance of N-channel MOSFET (Ω) (typ.17ω) I (MAX) = Maximum output current (A) Capacitor Selection Table 1 lists suggested tantalum or polymer capacitor values for typical applications. The ESR of both input bypass and output filter capacitors affects efficiency and output ripple. Output voltage ripple is the product of the peak inductor current and the output capacitor ESR. Highfrequency output noise can be reduced by connecting a.1μf ceramic capacitor in parallel with the output filter capacitor. See Table 2 for a list of suggested component suppliers. PC Board Layout and Grounding Careful printed circuit layout is important for minimizing ground bounce and noise. Keep the IC s GND pin and the ground leads of the input and output filter capacitors less than.2in (5mm) apart. In addition, keep all connections to the FB and LX pins as short as possible. In particular, when using external feedback resistors, locate them as close to FB as possible. To maximize output power and efficiency and minimize output ripple voltage, use a ground plane and solder the IC s GND pin directly to the ground plane. Maxim Integrated 11

12 Table 1. Suggested Components for Typical Applications COMPONENT Inductor Input Capacitor Output Capacitor COMPONENT ALUE (, 1A CURRENT LIMIT) COMPONENT ALUE (,.5A CURRENT LIMIT) Sumida CDRH6D28-22, 22µH Sumida CDRH4D28-22, 22µH Coilcraft DS3316P-223, 22µH Coilcraft DS168C-223, 22µH Sanyo POSCAP 6TPA47M, AX TPSD476M16R15, Taiyo Yuden UMK316BI15KH,.1µF Sanyo POSCAP 6TPA47M, AX TPSD226M16R15, 22µF Taiyo Yuden UMK316BI15KH,.1µF COMPONENT ALUE (,.25A CURRENT LIMIT) Sumida CR32-22, 22µH Sumida CR32-1, 1µH Murata CQH3C1K34, 1µH Murata CQH4N1K(J)4, 1µH Coilcraft DS168C-223, 22µH Coilcraft DS168C-13, 1µH Sanyo POSCAP 6TPA47M, AX TPSD16M16R15, 1µF Taiyo Yuden UMK316BI15KH,.1µF Table 2. Component Suppliers COMPANY PHONE FAX AX USA USA Coilcraft USA USA Coiltronics USA USA Murata USA USA Chip Information TRANSISTOR COUNT: 11 PROCESS: BiCMOS Nihon USA Japan USA Japan Sanyo USA Japan USA Japan Sprague USA USA Sumida USA Japan USA Japan Taiyo Yuden USA USA Maxim Integrated 12

13 Package Information For pricing, delivery, and ordering information, please contact Maxim Direct at , or visit Maxim Integrated s website at Maxim Integrated cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim Integrated product. No circuit patent licenses are implied. Maxim Integrated reserves the right to change the circuitry and specifications without notice at any time. The parametric values (min and max limits) shown in the Electrical Characteristics table are guaranteed. Other parametric values quoted in this data sheet are provided for guidance. Maxim Integrated and the Maxim Integrated logo are trademarks of Maxim Integrated Products, Inc. 2 Maxim Integrated Products, Inc. 13